EP0796101A1 - Compositions and methods for inhibiting fungal cell wall formation - Google Patents

Abstract

Disclosed herein are antifungal compositions having an oligosaccharide that includes an N-acetylhexosamine residue linked β(1→4) to a hexose and a biologically acceptable carrier. The isolation of the fungal enzyme chitin glucan β(1→4) transferase (CGβ(1→4)T) is disclosed along with methods for using this enzyme in an assay for antifungal agents. CGβ(1→4)T catalyses the formation of a β(1→4) linkage between the terminal reducing N-acetylglucosamine residue of chitin and the non-reducing glucose residue of β(1→3) linked glucans. Inhibitors of the enzyme, antifungals including such inhibitors, methods for the prevention and the treatment of fungal infections in animals and plants, and screening methods for identifying antifungals are also disclosed.

Description

COMPOSITIONS AND METHODS FOR INHIBITING FUNGAL CELL WALL

FORMATION

Field of the Invention

This invention pertains to antifungal compositions and to methods for using such compositions in the prevention and treatment of fungal infections in plants and animals. The invention also encompasses the enzyme that catalyzes the formation of certain fungal cell wall oligosaccharides that are formed by a specific covalent linkage between chitin and glucans.

Background of the Invention

Fungi are ubiquitous eukaryotic organisms of varying size and morphology. Fungi typically grow in two basic forms, yeasts and molds. Yeasts are single cell organisms that are usually spherical or ellipsoidal in shape and that generally reproduce by budding. Molds are multicellular organisms that generally form filamentous colonies. Examples of fungi include monomorphic yeasts and yeast-like organisms, including Candida, Cryptococcus, and Saccharomyces; monomorphic molds, such as Aspergillus and Coccidioides; and thermally dimorphic fungi, such as Blastomyces dermatitidis and Histoplasma capsulatum, which grow either in a yeast or a mold phase. Fungal cell walls determine the shape of fungal cells and are essential for fungal integrity. The cell walls include three types of structural polysaccharides: glucans (polymers of glucose (Glc) containing 0(l-*3) and 0(1→6) linkages), mannans (primarily glycoproteins with attached mannose chains), and chitin. Chitin is a linear polymer of N-acetylglucosamine (GlcNAc) residues joined by β(\→4) linkages. It is scattered throughout the cell wall, although it is mainly concentrated at the septal region. Because chitin is concentrated at the septal region, it is particularly instrumental in the reproduction of fungi by budding. The amount of chitin in the dry weight of the cell wall varies according to the fungal species. For example in S. cerevisiae, chitin comprises only 1-2% by weight, whereas in Sclerotium rol it may comprise up to 61 %.

The architecture of the fungal cell wall is defined by the organization of th cell wall constituents as well as by the constituents themselves. Several studies have sugges that different cell wall polysaccharides are covalently linked and particularly that chitin be covalently linked to the glucan component of the yeast cell wall. Mol et al. (F.E. Microbiol. Letts. , 41:95-99, 1987) disclose experiments in S. cerevisiae in which treatm of alkali-insoluble glucan with chitinase rendered the material alkali-soluble, suggesting t covalent linkage of glucan to chitin was responsible for its initial alkali insolubility. Siets et al. (J. Ge/z. Microbiol , 114:99-108, 1979) and Surarit et al (J. Gen. Microbiol. 134: 17 1730, 1988) studied Schizophyllum commune and Candida albicans, respectively, by digest the cell walls with both /3(1→3) glucanase and chitinase. Sietsma et al. suggest a model which amino acids are involved in the linkages between chitin and glucan. Surarit et conclude that the linkage involves a β(l→6) linkage between carbon-6 of GlcNAc and carbo of glucose.

Many fungi play an indispensable role in the cyclic transformation of orga matter, such as for example, in food and drug production. A broad range of fungi frequent causes of diseases in plants, however. An historical example of a fungal plant dise that had extensive adverse effects on man is the potato blight of the nineteenth century wh led to the starvation of over one million people.

Fortunately, of the thousands of known species of fungi, only a relatively s number cause diseases in animals. Most of these fungi are opportunistic pathogens, produc serious disease only in compromised individuals. However, because of an aging populat and an increase in the number of immunocompromised patients, such as those afflicted w acquired immunodeficiency syndrome (AIDS), patients undergoing cancer and corticoster therapy, and organ transplant recipients, fungal infections are increasing rapidly.

The major fungal animal pathogens in North America are Histoplas capsulatum, Coccidioides immitis, Blastomyces dermatitidis , Cryptococcus neoforma Candida species and Aspergillus species (Medically Important Fungi, Second Edition, Dav H. Larone, Ed. , American Society for Microbiology, Washington, D.C.).

Development of effective methods and compositions for the prevention and treatment of fungal infections is a critical goal of the agricultural and pharmaceuti industries. It has now been discovered that, in fiingal cell walls, two saccharide-based constituents are cross-linked in a β(l→4) covalent bond. The terminal reducing residue of a fungal chitin chain N-acetylglucosamine is covalently linked by a β(l→4) linkage to the non- reducing end of a /3(l-*3) glucan chain. Compositions incorporating these oligosacchandes or related compounds have antifungal properties in plants and animals.

Brief Description of the Drawings

Figure 1 is an illustration of the elution profile from a Bio-Gel P-2 column of a yeast wall fraction solubilized by digestion with glucanase and chitinase. Figure 2 is an illustration of the elution profile from a Bio-Gel P-2 column of compounds I, II, and III (Peaks A, B, and C of Figure 1, respectively) after acid hydrolysis.

Figure 3a is an illustration of the mass spectrometry determination of the molecular weight of compound I.

Figure 3b is an illustration of the mass spectrometry determination of the molecular weight of compound II.

Figure 3c is an illustration of the mass spectrometry determination of the molecular weight of compound HI.

Figure 4α is an illustration of the elution profile from a Bio-Gel P-2 column of compound I after treatment with the 50 μl of 100 mM citrate-phosphate buffer, pH 5.0. Figure 4b is an illustration of the elution profile from a Bio-Gel P-2 column of compound I after treatment with β-N-acetylglucosaminidase.

Figure Ac is an illustration of the elution profile from a Bio-Gel P-2 column of compound I after treatment with β-glucosidase.

Figure 5a is an illustration of the profile from paper chromatography of the products of a partial acid digestion of compound I.

Figure 5b is an illustration of the profile from paper chromatography of the products of enzymatic digestion of compound I.

Figure 6 is an illustration of the HPAEC profile of the products of periodate oxidation of the trisaccharide resulting from N-acetylglucosaminidase digestion of compound I.

Figure 7 is an illustration of the NMR spectra of compound I, laminaritriitol, and laminaribiitol. Figure a is an illustration of the profile from paper chromatography compound II after digestion witii β-glucosidase.

Figure 8b is an illustration of the profile from paper chromatography compound III after digestion with β-glucosidase. Figure 9 is a graphic illustration of a scheme for the generation of differ oligosaccharides by chitinase digestion.

Figure 10 is an illustration of the profile from paper chromatography o diacetylchitobiitol peak.

Figure 1 \a is an illustration of the elution profile from a Bio-Gel P-2 colu of material separated from diacetylchitobiitol by paper chromatography.

Figure lib is an illustration of the elution profile from a Bio-Gel P-2 colu of the material separated from diacetylchitobiitol after treatment with β- acety lglucosaminidase .

Figure l ie is an illustration of the elution profile from a Bio-Gel P-2 colu of the material separated from diacetylchitobiitol after treatment with β-glucosidase.

Figure 1 Id is an illustration of the elution profile from a Bio-Gel P-2 colu of the material separated from diacetylchitobiitol after treatment with β- acety lglucosaminidase and β-glucosidase.

Figure 12α is an illustration of the elution profile from a Bio-Gel P-2 colu of a pentasaccharide which elutes with triacetylchitotriitol.

Figure 12b is an illustration of the elution profile from a Bio-Gel P-2 colu of the pentasaccharide separated in Figure 12α after treatment with β-N-acety lglucosaminida

Figure 12c is an illustration of the elution profile from a Bio-Gel P-2 colu of the pentasaccharide separated in Figure 12α after treatment with β-glucosidase. Figure 13α is an illustration of the elution profile from a Bio-Gel P-2 colu of borotritide-reduced yeast cell walls after endoglucanase treatment and second borotriti reduction.

Figure 13b is an illustration of the elution profile from a Bio-Gel P-2 colu of borotritide reduced yeast cell walls after endoglucanase treatment. Figure 14α is an illustration of the elution profile from a Bio-Gel P-2 colu of wild type strain D3C cell walls after treatment with endoglucanase, reduction, a incubation with chitinase. Figure 14b is an illustration of the elution profile from a Bio-Gel P-2 column of strain ECY36-3C (chsl chs2: :LEU2) cell walls after treatment with endoglucanase, reduction, and incubation with chitinase.

Figure 14c is an illustration of the elution profile from a Bio-Gel P-2 column of strain ECY36-3D (chsl call/csd2) cell walls after treatment with endoglucanase, reduction, and incubation with chitinase.

Figure 14d is an illustration of the elution profile from a Bio-Gel P-2 column of wild type strain ECY36-3D pHV9a cell walls after treatment with endoglucanase, reduction, and incubation with chitinase. Summary of the Invention

Compositions having antifungal properties in plants and animals are provided. These compositions comprise:

(a) an antifungal effective amount of

(i) an oligosaccharide comprising an N-acetylhexosamine residue linked 0(1→4) to a hexose,

(ii) an inhibitor of an enzyme having as a first substrate, the terminal reducing N-acetylglucosamine residue of chitin and having as a second substrate the non-reducing glucose residues of (βl-*3) linked glucans, said enzyme catalyzing the formation of a (βl-*4) linkage between said N-acetylglucosamine and said glucose, or (iii) any combination thereof; and

(b) a biologically acceptable carrier.

Another aspect of the invention involves the isolation and identification of the fungal enzyme chitin glucan β(l→4) transferase (CGβ(l→4)T). This enzyme catalyzes the formation of a β(l→4) linkage between the terminal reducing GlcNAc residue of chitin and the non-reducing glucose residue of β(l→3) linked glucans.

The invention also includes methods for the prevention and the treatment of fungal infections in animals and plants. In such methods, prophylactically or therapeutically effective amounts of the antifungal compositions of the invention are administered to the subject plant or animal as a prophylactic measure or for the treatment of an existing fungal disease. High-throughput screening methods for identifying CGβ(l→4)T inhibitors are also provided. Detailed Description of the Invention

The present invention includes several different types of antifungal composit as well as methods, which may include the use of the enzyme CGβ(l→4)T, for identif such compositions. Preferred antifungal compositions comprise (a) an antifungal effective amount of

(i) an oligosaccharide having an N-acetylhexosamine residue li β(l-+4) to a hexose,

(ii) an inhibitor of CGβ(l→4)T, or (iii) any combination thereof; and (b) a biologically acceptable carrier.

N-Acetylhexosamine <3(1→4) Hexose Oligosaccharides

An oligosaccharide is a carbohydrate that is made up of 2-10 monosaccha units, any of which may be the same or different. (Grant & Hackh's Chemical Diction 5th Ed. , McGraw Hill Book Co. , (1987)). The present inventors have discovered that the wall of fungi, and particularly of S. cerevisiae yeast includes a specific covalent cross-lin between chitin chains and glucans. In the fungal cell wall, terminal reducing acetylglucosamine residues of chitin are linked j3(l→4) to the non-reducing glucose resi of /3(1→3) glucan chains. The oligosaccharides formed from N-acetylhexosamine resi linked β(l-*4) to a hexose are useful in antifungal compositions. Preferably, the hexos either or each constituent of the oligosaccharide is glucose.

Chitin-Glucan β(l→4) Transferase (CGβ(l→4)T)

A particular enzyme or class of enzymes (CGβ(l→4)Ts) catalyzes the forma of a β(l→4) linkage between an N-acetylhexosamine and a hexose and particularly betwee acetylglucosamine and glucose. The enzyme (whose identification is described below) ca used in the identification of antifungal agents and in the design of antifungal agents. The s moieties that are substrates of the enzyme(s) may be single residues or may be present as of oligosaccharides as in, for example, chitin and glucan. This enzyme is found i cerevisiae, and this enzyme or homologues thereof are found in other fungal species includ but not limited to, Candida, Aspergillus, Histoplasma, Cryptococcus, and Coccidio species. The enzyme(s) may be identified and isolated biochemically. An assay is devised to measure CGβ(l→4)T enzymatic activity in a quantitative manner. The assay preferably includes a mixture of chitin (Sigma Chemical Co., St. Louis, MO) and in vivo- labeled glucan or laminarin (prepared by growing yeast cells in the presence of [³H] or [¹ C] glucose and isolating alkali-soluble glucan according to Bowers, B. et al. , J. Bacteriol. 119:564-575, 1974), that is exposed to the enzyme. The product of the reaction is then digested with Zymolyase 100 T (Seikagaku America, Inc. - Rockville, MD), precipitated, and quantified. The source of the CGβ(l→4)T enzyme is a whole-cell extract of the fungal species studied, such as, for example, S. cerevisiae, produced by bead beating as described for glucan synthase (Kang et al. Proc. Natl. Acad. Sci, USA, 83:5808-5812, 1986).

Using a whole-cell extract as starting material and the enzymatic assay described above, CGβ(l→4)T is purified using methods that are well known in the art of protein chemistry. For example, the whole-cell extract may be fractionated by the sequential application of one or more of the following methods: ion-exchange chromatography, molecular sieve chromatography, and hydrophobic chromatography. These methods may be combined with extraction in detergents and/or mixtures of organic solvents that are known to those of ordinary skill in the art.

In each case, chromatographic fractions and/or extracts are assayed for CGβ(l→4)T activity and for total protein content. A balance sheet of purification i.e. total activity, total protein, and specific enzymatic activity, is compiled at each step. Fractions showing peak CGβ(l-*4)T activity are analyzed in parallel for their polypeptide profiles, using SDS-polyacrylamide gel electrophoresis. In this manner, fractions are obtained containing progressively higher specific activity for CGβ(l→4)T and fewer polypeptides.

The final, most purified CGβ(l→4)T preparation is then sequenced, using the N-terminal Edman degradation reaction. If the preparation contains only a single major polypeptide, the preparation itself is sequenced. If several polypeptides are present, they may be resolved on SDS-polyacrylamide gel electrophoresis and transferred to nylon or other suitable membranes or excised from the gel directly. The individual protein species may then be sequenced separately, using automated microsequencing equipment such as, for example, that available from Applied Biosystems (Foster, City, CA). CGβ(l→4)T-related peptide sequences of about 10-20 amino acid residues are obtained. Once a partial amino acid sequence of CGβ(l→4)T is obtained, stand reverse-genetic methods may be used to identify, isolate, and sequence the compl CGβ(l→4)T gene. See, for example, Molecular Cloning, A Laboratory Manual (2nd Sambrook, Fritsch and Maniatis, Cold Spring Harbor), or Current Protocols in Molecu Biology (Eds. Aufubel, Brent, Kingston, More, Feidman, Smith and Stuhl, Greene P Assoc , Wiley-Interscience, NY, NY, 1992). A series of degenerate oligonucleotides synthesized that collectively encode the partial peptide sequence identified as above. mixed oligonucleotides are used to screen genomic and/or cDNA libraries derived from starting organism. Positive clones are re-screened, and the DNA inserts are excised, diges with restriction enzymes, re-cloned, and re-screened. Finally, DNA fragments of 0.5-3 kb sequenced, and open reading frames (i.e. a DNA sequencing capable of encoding polypeptide) are determined.

The original peptide sequence used to design screening probes, as well deduced amino acid sequences derived from DNA clones, may also be used to des immunogenic peptides for the purpose of producing anti-CGβ(l→4)T antibodies. Peptides up to 40 residues may be synthesized chemically, and used, in conjunction with appropri carriers and adjuvants, as an immunogen in rabbits or other animals for the production polyclonal and monoclonal antibodies. Such antibodies are conveniently made using methods and compositions of Harlow and Lane, Antibodies, A Laboratory Manual, C Spring Harbor Laboratory, 1988.

Anti-CGβ(l→4)T antibodies are used to quantify and/or affinity purify CGβ(l→4)T enzyme, as well as to screen cDNA expression libraries described above for purpose of identifying and cloning CGβ(l→4)T-related sequences.

The CGβ(l→4)T DNA sequence and the amino acid sequence of the CGβ(l→ protein can be used as a basis for large-scale purification of the CGβ(l→4)T protein and the design and testing of CGβ(l→4)T inhibitors. CGβ(l-*4)T polypeptides, with or with additional sequence "tags" , may be synthesized in large amounts in E. coli, us commercially available vectors and bacterial hosts. An example of a suitable system is Invitrogen Xpress™ system (San Diego, CA). The sequence "tags" enable the rapid affi purification of the products, after which the "tags" may or may not be proteolytically remo to produce an authentic CGβ(l→4)T polypeptide. CGβ(l→4)T polypeptides may also be modified with a label capable of providing a detectable signal, either directly or indirectly. Exemplary labels include, but are not limited to, radioisotopes, fluorescent compounds, and the like. Labelled CGβ(l-*4)Ts can be used, for example, in assays for inhibitory compounds. According to the present invention, CGβ(l→4)T may be a monomer comprising a single polypeptide, may be a homomultimer, or may be a heteromultimeric molecule comprising different polypeptide chains. The polypeptide(s) may be modified by, for example, phosphorylation, sulfation, acylation, glycosylation, or other protein modifications. Furthermore, the CGβ(l→4)T may be isolated from its natural source or from heterologous organisms or cells, including, but not limited to, bacteria, yeast, insect cells, and mammalian cells, into which the gene or genes encoding CGβ(l-*4)T polypeptide(s) have been incorporated.

The present invention also contemplates derived proteins, and preferably fungal- derived proteins, with substantial sequence or functional homology to the CGβ(l→4)Ts described above. "Sequence homology" describes the relatedness of CGβ(l→4)Ts from different sources. Sequences are substantially homologous if at least about 70%, preferably at least about 80%, and most preferably at least about 90% of the two sequences are identical. Functional homology describes the stringency of hybridization conditions under which two sequences effectively or substantially hybridize. "Stringent" hybridization conditions are 0.1X SSC at 5°C. CGβ(l-*4)T may be derived from fungal sources such as Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatitidis, Cryptococcus neoformans, Candida species, and Aspergillus species such as Aspergillus fumigates. Preferably the CGβ(l→4)Ts are derived from other yeast-like organisms such as Candida, and most preferably, C. albicans. Non-S. cerevisiae CGβ(l→4)Ts may be identified and isolated by methods that are known in the art, such as, for example, antibody cross reactivity, PCR amplification from genomic DNA using degenerate oligonucleotide probes derived from the CGβ(l→4)T sequences identified as described above, low-stringency hybridizations using similar S. cerevisiae probes, and finally, functional cloning, in which a cDNA expression library derived from another species is used to transform and to complement an absent or defective CGT function in S. cerevisiae.

The identification and analysis of CGβ(l→4)T may also be carried out genetically. For example, one could select conditional mutants which are synthetically lethal with chsl mutants or osmotically remedial. Once yeast mutants that lack activity have b isolated, the CGβ(l→4)T gene(s) may be identified by transforming the mutant strains yeast genomic DNA libraries or yeast cDNA expression libraries. Transformed clones then screened for re-acquisition of CGβ(l-_*4)T activity. Finally, the DNA clones recovered from the yeast and are analyzed as described above for bacterial cloning syste

Enzvme Inhibitors

The present invention also encompasses agents that prevent the production the enzyme CGβ(l→4)T or that prevent the enzyme from catalyzing the formation of the acetylhexosamine β(l→4) hexose linkage described above. The inhibitory agents may comp peptides, oligosaccharides, lipids, derivatives of any of the foregoing, or other small orga molecules. Preferably, the inhibitors comprise modified sugars or oligosaccharides that also highly specific in their inhibitory activity, i.e. inhibit pathogenic fungi without advers affecting animal or plant physiology.

Disaccharide Linkage Inhibitors

Known inhibitors of disaccharide linkages, such as for example, allosamidin related analogues (Tet. Letts. , 35:4149, 1994); hydroquinones (Japanese Patent Publication 06-199649); moranoline (PCT Publication No. WO 94/04546); galactosyl-beta-l,3-gly (Scripps Res. Inst.); moenomycin A (Tetrahedron, 50:2029, 1994); di-and tri-saccharides intramolecular NH glycosidic linkages (Carbohyd. Res. , 252: 159, 1994); heteromet maltosides (J. Am. Chem. Soc , 116: 1569, 1994); and thiol carbohydrates such as th disclosed in Carboh. Res. , 250: 1, (1993), can be assayed for N-acetylhexosamine β(l- hexose linking inhibition. Suitable compounds can then be formulated into antifun compositions.

Modified N-Acetylhexosamine and Hexose

Other inhibitors of CGβ(l→4)T include, but are not limited to, compou comprising a terminal GlcNAc residue in which the carbon at the 1 position of the ring ( 1-carbon) is modified. (Carbon atom ring numbers are illustrated in Figure 7). Non-limit examples of suitable modifications at this position include, but are not limited to, (CH₂)_n- wherein n is an integer from 1 to 12, C_rCι₂ alkyl, unsubstituted aryl, aryl substitu preferably with C,-C₁₀ alkyl or alkenyl, or allosamizøline (Takehaski et al. , Tet. Letts. , 32:5123, 1991). Also included as inhibitors are hexose and preferably glucose molecules in which the carbon at the 4 position of the ring (the 4-carbon) is modified to prevent formation of the (31→4) GlcNAc linkage (see Figure 7). Suitable modifications of glucose include, but are not limited to, (CH₂)_n-OH, wherein n is an integer from 1 to 12,), C,-Cι₂ alkyl, unsubstituted aryl, aryl subtituted preferably with C,-C,₀ alkyl or alkenyl, or allosamizoline (Takehaski et al., Tet. Letts. , 32:5123, 1991). Either constituent of the oligosaccharide can be further modified at the other carbons.

Rational design of oligosaccharide-based inhibitors is based on an extensive enzymological analysis of CGβ(l→4)T activity. That is, the relative activity of different

CGβ(l→4)T substrates (including affinity and turnover time) is first tested for (31→4)-linked

GlcNAc polymers (chitin precursors) of different lengths, as well as for different configurations and lengths of (|S1→3) and (/31→6)-linked glucose polymers (glucan precursors).

Both GlcNAc- and glucose-based inhibitory compounds may comprise one or more sugar units. These compounds may also contain other modifications to enhance their efficacy, including those that cause the compound to be retained in the periplasmic space of the target organism. Preferably, inhibitors will be freely taken up across the fungal cell wall but will not cross the plasma membrane. The only limitation is that the modified compounds retain their capacity to bind CGβ(l-*4)T and to inhibit its enzyme activity.

Antifungals

Antifungal compositions are prepared from the N-acetylhexosamine residue β(l-*4) hexose oligosaccharides; CGβ(l→4)T inhibitors, including, but not limited to. modified N-acetylglucosamine or modified glucose; or any combination thereof as an active agent in a biologically acceptable carrier.

Suitable biologically acceptable carriers include, but are not limited to, phosphate-buffered saline, saline, deionized water, or the like. Preferred biologically acceptable carriers are physiologically or pharmacologically acceptable carriers.

The antifungal compositions include an antifungal effective amount of active agent. Antifungal effect amounts are those quantities of the antifungal agents of the present invention that afford prophylactic protection against fungal infections in plants and animals, and which result in amelioration or cure of an existing fungal infection in plants or animals. This antifungal effective amount will depend upon the fungus, the agent, and the host. amount can be determined by experimentation known in the art, such as by establishi matrix of dosages and frequencies and comparing a group of experimental units or subjec each point in the matrix. The antifungal compositions could act, for example, via inhibition transglycosidation, by a competitive or non-competitive mechanism. These compositions c also inhibit the reaction by mass action end product inhibition. Additionally, compositions could inhibit the cleavage of the chitin-glucan linkage that may normally o during growth or expansion of the cell wall. The antifungal active agents or compositions can be formed into dosage forms, such as for example, creams, ointments, lotions, powders, liquids, tablets, caps suppositories, sprays, or the like. If the antifungal composition is formulated into a do unit form, the dosage unit form may contain an antifungal effective amount of active ag Alternatively, the dosage unit form may include less than such an amount if multiple do unit forms or multiple dosages are to be used to administer a total dosage of the active ag Dosage unit forms can include, in addition, one or more excipient(s), diluen disintegrant(s), lubricant(s), plasticizer(s), colorant(s), dosage vehicle(s), absorp enhancer(s), stabilizer(s), bactericide(s), or the like.

The antifungal agents and compositions of the present invention are useful preventing or treating fungal infections in plants and animals. Fungal infection preven methods incorporate a prophylactically effective amount of an antifungal agent or composit A prophylactically effective amount is an amount effective to prevent fungal infection and depend upon the fungus, the agent, and the host. These amounts can be determ experimentally by methods known in the art and as described above. Fungal infec treatment methods incorporate a therapeutically effective amount of an antifungal agen composition. A therapeutically effective amount is an amount sufficient to stabilize o ameliorate a fungal infection. Preferably, this amount will yield a reduction to less than 1 of the amount of fungus present at initiation of treatment. This amount also depends upo fungus, the agent, and the host, and can be determined as explain above. The prophylactically and/or therapeutically effective amounts can administered in one administration or over repeated administrations. Therape administration can be followed by prophylactic admimstration, once the initial fungal infection has been resolved.

The antifungal agents and compositions can be applied to plants topically or non- topically, i.e., systemically. Topical application is preferably by spraying onto the plant. Systemic admimstration is preferably by application to the soil and subsequent absorption by the roots of the plant. For example, the antifungal composition that includes an N- Acetylhexosamine (β-_*4) hexose oligosaccharide can be administered in an amount that effectively saturates the fungus and its environment, thereby inhibiting the CGβ(l→4)T enzyme. The antifungal agents and compositions can be administered to animals topically or systemically. Systemic administration with respect to animals include both oral and parental routes. Parental routes include, without limitation, subcutaneous, intramuscular, intraperitoneal, intraduodenal, and intravenous administration.

Screening Assays

Antifungal compounds may be identified using screening methods including, but not limited to, high-throughput screening methods that are based on a modified CGβ(l→4)T assay. In addition, a screen for compounds that differentially affect the viability of chsl versus chs3 imttant yeast strains (Gaughran et al., J. Bacterial, 176:5857-5860, 1994) would be expected to detect inhibitors of CGβ(l→4)T. Another screening method involves growing yeast cells in an osmotic remedial medium in the present of potential inhibitors, followed by an assay for alkali-soluble versus alkali-insoluble glucan. This ratio would increase upon inhibition of CG(1→4)T. In an alternate embodiment, compounds are screened for their ability to bind to CGβ(l→4)T polypeptides purified as above. Assays involve screening test inhibitory compounds from large libraries of synthetic or natural compounds. Synthetic compound libraries are commercially available from, for example, Maybridge Chemical Co. (Trevillet, Cornwall, UK), Comgenex (Princeton, NJ), Brandon Associates (Merrimack, NH), and Microsource (New Milford, CT). A rare chemical library is available from Aldrich Chemical Company, Inc. (Milwaukee, WI). Alternatively, libraries of natural compounds in the form of bacterial, fungal, plant and animal extracts are available from, for example, Pan Laboratories (Bothell, WA) or MycoSearch (NC), or are readily producible. Additionally, natural and synthetically produced libraries and compounds are readily modified through conventional chemical, physical, and bioche means.

A preferred screening method includes the steps of (a) contacting a CGβ(l enzyme as described above with an N-acetylhexosamine and a hexose in the presence o antifungal candidate to form a test mixture; (b) contacting the enzyme with the same acetylhexoseamine and hexose in the absence of the candidates to form a control mixtur (c) detecting any formation of a β(l→4) linkage between the N-acetylhexoseamine and hexose in the test mixture and in the control mixture; (d) comparing the efficienc formation of that linkage in the test mixture and in the control mixture; and (e) selectin an antifungal compound the test candidate compound that causes a decrease in the effici of formation of the linkage in the test mixture relative to the efficiency of formation of linkage in the control mixture.

Once a particular test compound has been identified in a high-throughput scr its inhibitory activity is then confirmed by measuring its effect on CGβ(l→4)T activity standard (i.e. low-throughput) assay. Finally, the compound is tested for two properties: the ability to inhibit fungal growth; and (2) a lack of effect on animal and/or plant c

Fungal growth is measured by any method well-known in the art, for example, optical de of a liquid culture or colony formation on agar. The potential toxic ity of an agent mammalian cells is measured by monitoring its effect in a typical mammalian cell culture, s as, for example, L-cells.

Description of the Preferred Embodiments

The following examples illustrate the invention without limitation.

Materials

Enzymes and Reagents β-N-Acetylglucosaminidases from jack beans or from Diploco pneumoniae(Oxfoτd Glycosystems, Inc.-Rosedale, NY). β-N-Acetylglucosaminidase from beef kidney and β-glucosidase (Boehri Mannheim-Indianapolis, IN). β(l→3) endoglucanase.

Zymolyase 100 T (Seikagaku America, Inc.-Rockville, MD). Glusulase (Dupont Co.-Wilmington, DE).

Sodium [³H]borohydride (Naβ³H₄) (American Radiolabeled Chemicals Inc. -St. Louis, MO) - 100-500 mCi/mmol, or ICN Biomedicals, Inc. -Costa Mesa, CA - 100 mCi/mmol). [l-¹⁴C]glucose (American Radiolabeled Chemicals - 50-60 mCi/mmol).

Chitinase from Serratia marcescens was prepared as described in Roberts and Cabib, Anal. Biochem. , 127:402-412 (1982).

S. Cerevisiae Yeast Strains and Yeast Growth D3C (MATa ura3) - wild type.

ECY36-3C (MATa chsl-23 chs .LEUl trpl-1 ura3-51 leul-1) - CHsl- and Chs2-deficient.

ECY36-3D pHV9A - contains plasmid pHV9A which carries the CAL1/CSD2 gene that restores Chs3 activity. Strains D3C and ECY36-3D were grown in YEPD (1 % yeast extract, 2% peptone, 2% glucose), and strains ECY36-3C and ECY36-3D pHV9A were grown in minimal medium (2% glucose, 0.7% Difco yeast nitrogen base without amino acids) plus nutritional requirements. In all cases growth was at 30°C.

Procedures

Preparation of Cell Walls and Digestion with Glucanase and Chitinase.

In a typical preparation, 16.3 g (wet weight) of cells (Strains D3C or ECY36-3C which has a higher chitin content). (See, Shaw et al. , J. Cell. Biol. , 114: 111-123, 1991) were harvested in the exponential phase of growth. The harvested cells were suspended in about 45 ml of 50 mM Tris chloride, pH 7.5, and were added to 75 grams of glass beads (0.5 mm diameter, Braun-Melsungen, Germany) in the intermediate size vessel of a Bead-Beater (Biospec Products, Bartiesville, Ohio). After cooling the suspension to 5° C, the Bead-Beater was operated for two 3 minute periods, with a 10 minutes cooling period inbetween. The extract was aspirated from the glass beads, and the aspirated extract was washed several times with small portions of Tris buffer. Cell walls were sedimented by centrifugation at 4,000 x g for 10 minutes, the pellets were washed five times with Tris buffer. The washed cell walls were suspe in the same buffer to a final volume of 495 ml. β(l→3) endoglucanase (Zymolyase 100 T) (4.3 ml of a 7.5 mg/ml solutio 50 mM sodium phosphate, pH 6.3) was added. The suspension was incubated at 37° C shaking, and the absorbance at 660 nm was monitored. After about one hour, the absorb had decreased to about 5% of the original value.

The suspension was centrifuged for 10 minutes at 16,000 g. The pellet washed twice with Tris buffer and twice with 1 % SDS. The suspension was placed f minutes in a boiling water bath in the second SDS washing. The pellet was then washed t more times with water and was suspended in water to a concentration of 10 mg chiti (about one ml in the preparation described.) The ratio of total N-acetylglucosamine to glucose at this step was 1:0.7.

600 μl of the resultant suspension was treated with 600 μl of NaB ³H₄ (6 in dimethylformamide at room temperature for 5 hours. The reaction was terminated by addition of 300 μl of 1 M acetic acid, and the insoluble material was washed by repe centrifugation, followed by suspension in 50 mM potassium phosphate at pH 6.3. washed, reduced chitin was digested overnight at 30 °C with 600 μl (184 mU) of marcescens chitinase. Any insoluble residue was removed by centrifugation. The supernatant fluid was used directly for Bio-Gel P-2 chromatography. compounds isolated from the eluate of the Bio-Gel column were again reduced with an ex of unlabeled sodium borohydride and repurified by Bio-Gel chromatography prior to fur analysis.

High Performance Anionic Exchange Chromatography

Samples were analyzed on a Dionex high performance amino exch chromatography (HPAEC) instrument equipped with a pulsed amperometric detector M PAD2, and pellicular anion-exchange columns (PA-1 or MA-1, 4 x 250 mm). The Di eluent degas module was used to sparge and pressurize the eluents with the helium set at p.s.i. The flow rate was maintained at 0.8 ml/min. The applied pulse potential was 0.0 and detector sensitivity was set at 300 nA. The system was used at ambient temperat Samples were applied via a Dionex microinjection valve with a 50-μl loop. Areas unde curve were recorded and integrated with a Spectra-Physics integrator. The eluent contained 100-500 mM NaOH.

Paper Chromatography

The solvent used for paper chromatography was butanol/pyridine/ water 6:4:3, and the paper was Whatman No. 1 or No. 3 MM. Carbohydrate Determinations

Total carbohydrate was measured with the anthrone reagent (See Trevelyan et al., Biochem. J. , 50:298-303 (1952)) and glucose was measured by glucose oxidase (Glucose Trinder Kit - Sigma Chemical Co. - St. Louis, MO). Free GlcNAc was quantified by the method of Reissig et al., J. Biol. Chem. , 217:959-966, 1955) and combined GlcNAc by the same method after digestion of 60 μl of sample (0.3-0.5 μmol of combined GlcNAc) with 60 μl Glusulase, 60 μl chitinase and 5 μl 1 M sodium phosphate, pH 6.3, for 45 minutes at 30°C.

Mass spectrometry Chemical iodization mass spectra were obtained with a Finigan 1015D spectrometer, using ammonia as the reactive gas.

NMR Spectrometry

'H and ¹³C NMR spectra were measured at ambient temperature with a Varian FX 300 or a Varian Gemini spectrometer, operating at 300 MHz for protons and 75 MHZ for ¹³C. Chemical shifts found in the spectra recorded for solutions in CDC1₃ and D₂O are reported, respectively, with Me₄Si and methanol (δ MeOH vs. δMe₄Si 49.0) as internal standards. Proton-signal assignments were done by COSY or homonuclear decoupling experiments. The non-equivalent germinal proton resonating at lower field is denoted Ha and the one at higher field Hb. Carbon signal assignments were based on heteronuclear shift- correlated 2D experiments (HECTOR).

General Synthesis ofβ-D-GlcNAc (l→ό)-D-Glc

Optical rotations were measured at 25° C with a Perkin Elmer Model 241 MC automatic polarimeter. All reactions were monitored by thin-layer chromatography on pre- coated slides of silica gel G F254 (Analtech). Detection was effected by charring with 5% sulfuric acid in ethanol or, when applicable, with UV light. Preparative chromatography was performed by gradient elution from columns of Silica Gel 60 (Merck, No. 9385). Reacti requiring anhydrous conditions were performed under dry nitrogen using common laborat glassware and reagents and solvents were handled with gas-tight syringes. Solutions in org solvents were dried with anhydrous sodium sulfate and concentrated under a vacuum at 40 1,2,3,4-Tetra-O-acetyl-β-D-glucopyranose (Sigma Chemical Co.) and bromo-2-deoxy-2 phtalimido-3,4,6-tri-O-acetyl-α:, β-D-glucopyranose (Toronto Research Chemicals Inc.) used as supplied.

1,1,3, 4-Tetra-0-acetyl-6-0- (3, 4, 6-tri-O-acetyl-l-deoxy-l-N-phtalimido-β-D- glucopyranosyl-β-D-glucopyranose

1,2,3,4-Tetra-O-acetyl-β-D-glucopyranose (0.7 g, 2 mmol) was dissolved in nitromethane (30 ml), and 4A molecular sieve (1 gram) was added. After cooling to 30 the reaction mixture was stirred for 30 minutes, and sym-collidine (0.28 ml, 2 mmol) silver triflate (0.54 gram , 2. 1 mmol) were added . F inal bromo-2-deoxy-2-N-phtalimido-3,4,6- tri-O-acetyl-α, β-D-glucopyranose (1 gram, 2 m dissolved in nitromethane (5 ml) was added dropwise. After 1 hour, additional portions sym-collidine (0.056 ml, 0.4 mmol), silver triflate (0.1 gram, 0.4 mmol), bromo-2-deoxy-2-N-phtalimido-3, 4, 6-tri-O-acetyl-α, β-D-glucopyranose and (0.2 gram, mmol) were added. The reaction mixture was stirred for 2 hours at -30° C. At this po 1,2,3,4-Tetra-O-acetyl-β-D-glucopyranose was no longer detected by thin la chromatography (TLC -toluene/acetone 6: 1) After filtration through Celite, the filtrate washed with saturated sodium bicarbonate and with water, dried with sodium sulf concentrated, and purified on a silica gel column (toluene/acetone 10: 1) to yield 1,2,3.4-te O-acetyl-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phtalimido-β-D-glucopyranosyl-β glucopyranose.

Properties are summarized below. [α]_D + 18.47° (c. 7.82, chloroform); Η NMR (CDC1₃) 6; 7.89-7.3 (m, 6H, Ph), 5.75 (dd, 1H, J₃ ,₄. 9.1 Hz, J₂.,₃. 10.6 Hz, H-3'), 5.59 (d, 1 H, J,_,2 7.9 Hz, H-l), 5.44 (d, 1 H, J_ι 8.2 Hz, H-l'), 5.16 (dd, 1 H J₄._,5 9.4 Hz, H-4'), 5.13 (dd, 1 H, J_2,s 9.9 Hz, H-3), 5.01 (dd, lH,H-2), 4.90 (dd, 1H, J_4,5 9.8 Hz, H-4), 4.34 (m, 2 H, H-2M H-5',), 4.17 (dd, 1 H, J₅-₆._b 2.4 Hz, H-6_b), 3.88 (m, 1H, H-5'), 3.72 (m, 1 H, H-5), 3.62 (m, 2H, H-6_a, H-6_b), 2.14 (s, 3 H, COCH₃), 2.03 (s, 3 H, COCH₃); 1.99 (s 3 H, COCH₃), 1.93 (s, 3H, COCH₃, 1.93 (s, 3 H, COCH₃), 1.89 (s, 3 H, COCH₃ (s, 3 H, COCH₃), 1.85 (s, 3 H, COCH₃), ^,3C-NMR (CDC1₃) δ:170.86, 170.27, 170.16, 169.60, 169.32, 169.21, 168,86 (COCH₃), 97.94 (C-1'), 91.51 (C-1), 73.63 (C-5), 72-64 (C-2), 71.87 (C-5'), 70.29 (C-4), 68.82 (C-4'), 68.27 (C-3), 67.33 (C-6), 61.88 (C-6'), 54.22 (C-2'), 20.63, 20.58, 20.48, 20.48, 20.37, 20.26, 20.20 (COCH₃).

6-0-(l-acetamido-l-deoxy-β-D-glucopyranosyl)-a,β-D-glucopyranose. l,2,3,4-Tetra-O-acetyl-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phtalimido-β-D- glucopyranosyl-β-D-glucopyranose (0.055 gram, 0.072 mmol) was dissolved in anhydrous methanol (10 ml), and sodium methoxide in methanol (1 M, 0.0 ml) was added. The reaction mixture was stirred at room temperature for 4 hours. At this time, l,2,3,4-Tetra-O-acetyl-6- O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phtalimido-β-D-glucopyranosyl-β-D-glucopyranose was no longer detected by TLC (propanol/ethyl acetate/ water 4:2: 1). After neutralization with Amberlite 120 (H+) and filtration, the filtrate was concentrated and dried under a vacuum. The crude product was dissolved in methanol (5 ml), and anhydrous hydrazine (14 μl, 0.45 mmol) was added. The reaction mixture was kept under reflux (65° C) for 2 hours, at which point starting material was consumed as monitored by TLC (ethyl acetate/ethanol/water, 8:4:2). After cooling to room temperature, acetic anhydride (0.5 gram, 0.46 ml, 4.9 mmol) was added, and the mixture was stirred for 20 minutes. When the starting material was no longer detected by TLC (propanol/ethylacetate/ water 2: 1: 1), the reaction mixture was concentrated and purified on a Bio-Gel P-2 extra-fine, 2 x 90 cm column to yield 6-O-(2- acetamido-2-deoxy-β-D-glucopyranosyl)-α , β-D-glucopyranose . Properties are summarized below. [α]_D + 3.82 (c 17.00, water); ^lH NMR (D₂O) δ: a: 5.21 (d, 1H, J , 3,7 Hz, H-l), 4 (d, 1 H, J 8.3 Hz, H-l¹), 4.11 (dd, 1 H, J_{5 6a} 2Hz, J^ 11.4 Hz, H-6 , 3.94 (m, 2H, H- H-5), 3.81 (dd, 1H, J_{5 6} 4.3 Hz, H-6_b), 3.73 (m, H-6'_b), 3.71 (m, H-2', H-3), 3.68-3.46 4 H, H-3', H-2, H-5', H-4), 3.41 (dd, 1 H, J_s. ₄. 6.1 Hz, J_{4 5}- 9.6 Hz, H-4'), 2.07 (s, 3 COCH₃); β: 4.63 (d, 1 H, J_1>2 7.9 Hz, H-l), -4.57 (d, 1 H, J,. ,., 8.4 Hz, H-l '), 4.17 (dd, 1 H, J_{5 6a} Hz, J^,, 11.5 Hz, H-6a), 3.75 (m, 2 H, H-2', H-6b), 3.73 (m, H-6'_b), 3.68-3,46 (m, 4 H, 3', H-5, H-5', H-3) 3.41 (dd„ 1 H, J_{3 ι4}. 6.1 Hz, J_{4 5}. 9.6 Hz, H-4'), 3.38 (dd, 1 H, J 5.6 J 9.2 Hz, H-4), 3.24 (dd, 1 H, J_{2 3} 9.2 H-2), 2.07 (s, 3 H, COCHa);

¹³C NMR (D²O) δ: α: 175.11 (COCH₃), 101.98 (C-1 '), 92.45(C-1), 76.11 (C-5'), 73.97 3'), 73.02 (C-3), 71.69 (C-2), 70.57 (C-5), 70.18 (C-4), 69.83 (C-4'), 68.71 (C-6), 55.73 2'), 22.40 (COCH3); β: 175.11 (COCH₃), 102.06(C-1 '), 96.31 C-1), 76.11 (C-5'), 76.05 (C-5), 75.06 (C-3), 74 (C-2), 73.97 (C0-3'), 70.18 (C-4), 69.83 (C-4'), 68.95 (C-6), 55.73 (C-2'), 22.40 (COC

Isolation and Identification of the β(l→4) Linkage Example 1 - Between Chitin and β(\→3>) Glucan in S. cerevisiae

To isolate the linkage region between chitin and β-glucan, yeast cell walls w digested with a β(l-3) endoglucanase (zymolyase), with the expectation of forming s glucose oligosaccharide stubs attached to the chitin. After removal of all the solubili material, the insoluble fraction was reduced with sodium borotritide, to label the reducing e of the stubs. This treatment also reduced and labeled GlcNAc residues at the reducing en chitin chains not bound to glucan. The labeled material was then digested with S. marcesc exo-chitinase, an enzyme that sequentially cleaves diacetylchitobiose residues from chi starting from the non-reducing end (See, Roberts et &\. , Anal. Biochem. , 127:402-412, 198

The chitinase-solubilized fraction from 6 mg of glucanase-resistant insolu residue was applied to an extra-fine Bio-Gel P-2 column (2 x 90 cm) and was eluted with

M acetic acid. (In Bio-Gel P-2 column chromatography, each GlcNAc residue, whether f or combined, counts as two hexose residues in determining relative elution positions (S

Yamashita et al., Meth. Enzymol. , 83: 105-106, 1982). Thus, diacetychitobiose elutes in same volume as a glucose tetrasaccharide. This is not true of paper chromatography, where the mobility of each monosaccharide depends on the solvent used, and, within the same series, is inversely proportional to molecular weight). 1.8 ml fractions were collected, and a 20-μl portion of each sample was counted. Results are illustrated in Figure 1. "1 " indicates the void volume position, and

"2-8" indicate the positions of the following standards: 2, triacetylchitotriitol (or laminarihexaitol); 3, laminaripentaitol; 4, diacetylchitobiitol (laminaritetraitol); 5, laminaritriitol; 6, GlcNAc-ol (or laminaribiitol); 7, glucitol; 8, Glc ([¹⁴C]) glucose was added as internal standard). Two of the major radioactive peaks correspond to diacetylchitobiitol (Figure 1 , peak 4) and triacetylchitotriitol (Figure 1, peak 2), which originate from free chitin chains containing an even and an odd number of GlcNAc residues, respectively (See Kang et al. , J. Biol. Chem. , 259:14966-14972. 1984). A large peak in the void volume and some additional minor peaks were also detected. The latter appeared to be candidates for the linkage region and were named Peaks A (Compoimd I), B (Compound II), and C (Compound HI). Peak A contained both N-acetylglucosamine and glucose, whereas Peaks B and C contained only glucose.

Structure of Compound I (Peak A. Figure 1) Acid Hydrolysis/HPAEC

5 nmol each of compounds I, II or III were evaporated to dryness under nitrogen, and were hydrolyzed with 25 μl of 2M TFA at 100°C for 2 hours, evaporated under nitrogen and diluted to 200 μl of water. A 50 μl sample was analyzed by HPAEC in a PA-1 column as described above. Results are illustrated in Figure 2. Acid hydrolysis of Peak A gave rise to glucosamine, glucose and glucitol, in the ratio 1.1:2:0.9 as illustrated in Figure 2.

Mass Spectrometry

100 nmol of each of compounds I, II, and III were evaporated to dryness under nitrogen. The residue was dissolved in 200 μl of pyridine, and 200 μl of acetic anhydride were added. After overnight incubation at room temperature, a few drops of toluene and of methanol were added, and the solution was evaporated to dryness. The dissolution-evaporation was repeated several times, first with toluene, then with methanol. Finally, the sample was dissolved in 20 μl of dichloromethane and was analyzed by mass spectrometry. Bec ammonia was used as the reactive gas, the ammonium ion weight was added to the calcu molecular weight. Results are illustrated in Figures 3α-c.

The molecular weight of the acetylated compound, as measured by spectrometry, was 1316, compared to a value of 1315 for an acetylated tetrasacch consisting of a residue each of GlcNAc and glucitol and two glucose residues. (This incl the weight of ammonium ion). This composition is also reflected in the elution of volu

Peak A (Figure 1) which corresponds to a reduced glucose pentasaccharide standard.

β-N-acetylglucosaminidase or β-glucosidase Treatment

Compound I (Peak A - Figure 1) was treated with N-acetyl-β-glucosamini and β-glucosidase to determine the manner and position at which the GlcNAc was attac Aliquots ( ~ 130 pmol, 130,000 cpm) of compound I were evaporated to dryness and redissolved in 50 μl of 100 mM citrate-phosphate buffer, pH 5.0 (Figure 4a); in the s buffer plus 5 μl (135 mU) of β-N-acetylglucosaminidase from jack beans (Figure 4b); a 60 μl of 0.1M acetate buffer pH 4.5, containing 0.1 mg of sweet almond β-glucosidase (Fi 4c). All mixtures were incubated 16 hours at 37°C, then diluted with 300 μl water subjected to Bio-Gel P-2 chromatography. Standards were: 1 , triacetylchitotriitol diacetylchitobiitol; 3, laminaritriitol; 4, laminaribiitol; 5, glucitol; 6, glucose ([¹⁴C]) glu was the internal standard).

Results are illustrated in Figure 4. The positions of peaks A, B and C are indicated.

Whereas β-glucosidase treatment had no effect on the elution positio compound I (Figure 4c), incubation with β-N-acety lglucosaminidase moved it to the posi of laminaritriitol (Figure 4b). This result showed that the GlcNAc in compound I was t at the non-reducing end and was attached to a trisaccharide by a β-linkage.

Partial Acid Digestion

A sample of compound I ( — 25 pmol , 25,000 cpm) was evaporated to dry under nitrogen and was hydrolyzed with 50 μl of 0.05 M trifluoracetic acid for 2 hou

100°C. The hydrolyzate was subjected to paper chromatography. Segments (1-cm) o paper were counted. Standards: 1, glucose ([^I4C] glucose internal standard); 2, glucito laminaribiitol; 4, laminaritriitol or gentiobiitol; 5, laminaritetraitol; 6, gentiotriitol; 7, laminaripentaiol.

Results are illustrated in Figure 5a. Only products that still retained the labeled sorbitol were detected by the radiometric assay. After partial acid hydrolysis, three additional peaks were detected, which migrated as Glc(βl-3)Glc(βl-3)Glc-ol (or Glc(l-6)Glc-ol), Glc(βl-

3)Glc-ol and Glc-ol. All of these compounds would be expected if GlcNAc were attached to a reduced laminaritriose.

Partial Enzymatic Digestion Aliquots of compound I (10 pmol, 10,000 cpm each) were evaporated to dryness and were dissolved in 30 μl of 100 mM citrate-phosphate buffer, pH 6.0. Both aliquots were incubated 16 hours at 37 °C, one with 7.5 mU of β-N-acetylglucosaminidase from Diplococcus pneumonia and the other with the same enzyme plus 0.02 mg of β- glucosidase from sweet almonds. Both samples were subjected to paper chromatography as above. Standards: 1, glucose; 2, laminaribiitol; 3, sophoritol; 4, cellobiitol; 5, laminaritriitol or gentiobiitol; 6, gentiotriitol.

Results are illustrated in Figure 5b. (•) - incubated with N- acety lglucosaminidase; (o) - incubated with both enzymes. The tentative structure of compound I and of the hydrolysis products are shown, where an open square stands for GlcNAc, an open circle for Glc and a filled circle for glucitol.

Partial hydrolysis with β-N-acetylglucosaminidase gave rise to a peak in the position of the original material and another one moving as Glc(βl-3)Glc(βl-3)Glc-ol or Glc)βl-6)Glc-ol. This indicates that the glucose trisaccharide cannot be gentiotriitol, since the latter (standard 6 in Figure 5b) moves much more slowly than the product of the reaction. When both β-N-acetylhexosaminidase and β-glucosidase were allowed to act on compound I, the product comigrated with Glc(βl-3)Glc-ol and was clearly different from the 1-2, 1-4 and 1-6 isomers (Figure 5b).

In separate experiments it was found that laminaribiitol is resistant to β- glucosidase. Taken together, the above results are consistent with a structure in which GlcNAc is β-linked to reduced laminaritriose.

Trisaccharide Periodate Oxidation A portion of compound I (60 nmol) was digested with jack bean β acetylglucosaminidase and was subjected to Bio-Gel P-2 chromatography essentially described above. The recovered trisaccharide (50 μl) was oxidized with 700 nmol of sodi metaperiodate for 70 hours at 4°C in the dark. Ethyleneglycol (1 % , 23 μl) was added. A 2 hours at room temperature, 40 μl of 0.1 NaOH and 50 μl of sodium borohydride in 0.01 NaOH were added. Incubation was continued for 3 additional hours. The sample evaporated to dryness under nitrogen, dissolved in 100 μl of 2 M trifluoracetic acid, heated at 100°C for 2 hours. After evaporation to dryness, the residue was dissolved in μl water and a 50-μl portion was subjected to HPAEC on a PA-1 column with 0.2 M Na as solvent.

Laminaribiitol and laminaritriitol (50 nmol of each) were subjected to the sa treatment and chromatographed.

Results are illustrated in Figure 6. The large peak at 2.34-2.36 minute ethyleneglycol. Glucose (retention time 5.15-5.25 min) was present in the samples result from oxidation of laminaritriitol or of the trisaccharide from compound I, but not in the from laminaribiitol.

Any configuration of the glucose to glucose linkage other than 1→3 would h resulted in the destruction of both Glc residues. However glucose was recovered a oxidation, indicating that the terminal and penultimate glucose residues were bound in a 1 linkage.

'H-NMR Spectrum From ^]H NMR studies of reduced laminaritriose, it was concluded that anomeric proton of the internal residues (H'-l from ring C, see Figure 7 top) resonates 4.65 ppm. Only two doublets were found, with chemical shifts of 4.58 ppm and 4.48 pp in the Η-NMR spectrum of Compound I (data not shown). Therefore, it may be infer that the 4.58 ppm doublet corresponds to the anomeric protons H'-l and H"-l of I. Beca the doublet is partially overlapped by the HOD signal, the signal cannot be quantified integration to confirm that it is originated in two protons. The corresponding coupl constant J₁.₂-=Jι--₂-- is 7.9 Hz, as expected for a β linkage. Given this attribution of the 4.58 ppm signal, the doublet at 4.48 ppm must represent the anomeric proton (H'"-l) of the GlcNAc unit. This chemical shift is in good agreement with known shifts for branched penta- and hexasaccharides bearing GlcNAc at the nonreducing end (4.45-4.58 ppm). See, Kahn et al., Carbohyd. Res. 262:283-295, 1994. The coupling constant J,.., ₂... of the 4.48 ppm doublet is 8.3 Hz, a value typical of β-linked units.

Analogous Compound Comparison

GlcNAc(βl-6)Glc was synthesized. This compound eliminated the 1→6 linkage as a possibility for the chitin/N-acetylglucosamine linkage because the synthetic compound was decomposed by beef kidney β-N-acetylglucosaminidase whereas compound I was resistant (data not shown). The possibility that GlcNAc was attached to Glc by a 1-2, 1-3 or 1-4 linkage still remained. Since the amount of material available was insufficient for methylation analysis, NMR spectroscopy was employed. "C-NMR Spectrum Approximately 1 μmol of compound I was evaporated to dryness several times with D₂O, and then was dissolved in 600 μl of D₂O. The spectrum was measured continuously for 5 days, as described above. Interpretation of the spectra was based on identification of the signals in two-dimensional COSY and HECTOR spectra of standard laminaribiitol, laminaritriitol and GlcNAc(βl-6)Glc standards. Results are illustrated in Figure 7. Attribution of peaks to different carbons are shown for the spectrum of Compound I. For each bracketed group of peaks, the carbon listed on top refers to the first peak from left under the bracket. The other carbons follow from top to bottom and from left to right, respectively. The position at which the C4" peak was expected is shown, together with that where it was actually found (arrow). Model oligosaccharides laminaribiitol and laminaritriitol and GlcNAc(βl-6)Glc were studied by 2D NMR spectroscopy (COSY, HECTOR). The groups of signals belonging to the different carbons of D-sorbitol (C), D-glucopyranosyl units (C and C") and 2- acetamido-2-deoxy-D-glucopyranosyl (C" ') were identified. The largest deviation of chemical shifts of the C" unit of compound I compared to the corresponding unit of reduced laminaritriose was expected at the carbon involved in the glycosidic bond. C"-2 and C"-6 were eliminated as participants in the bond, because their chemical shifts, 73.55 and 73.35 ppm for C"-2 and 60.65 and 60.86 ppm for C"-6, are the same for compound I and for reduced laminaritriose. If the glycosidic linkage were at position C"-3, one of the signa the region 75.41-75.97 ppm would move to lower field in the spectrum of compoun because this is the area in which carbons C-5, C"-5 and C"-3 are located. This shift di occur. Also, in the spectrum of compound I, signals for five carbons should appear i region 68.35-70.83 ppm, representing C-5 and all four C-4 carbons (C-4, C-4, C"-4, C However, only four signals were found in this area, and they were assigned to carbons C-5, C"-4 and C-4. This meant that carbon C"-4 signal was moved to lower field, w it can be found at 78.68 ppm (Figure 7), due to the large positive α-effect of the glyco linkage at that position (18). Therefore, the glycosidic linkage between GlcNAc and G compound I was β(l→4). The complete structure of the substance GlcN Ac(β l→4)Glc(β l→3)Glc(β l→3)Glc-ol .

Structure of Compound in Peak B - Figure 1 Acid Hydrolysis Complete acid hydrolysis of Compound II (Peak B, Figure 1) gave ris glucose and sorbitol in a 2.0:1.0 ratio (See Figure 2).

Mass Spectrometry

The molecular weight, as measured by mass spectrometry was in agree with this result (calculated 1028; found 1028). See Figure 3b.

β-Glucosidase Digestion

A portion (5000 cpm) of compound II was evaporated to dryness and disso in 30 μl of acetate buffer at pH 4.5, containing 10 μg of sweet almond β-glucosidase. 16 hours of incubation at 37° C, the sample was analyzed by paper chromatography.

Results are illustrated in Figure 8α. (O)-digested sample; (•) incubated con

Digestion of compound II with β-glucosidase followed by paper chromatogr showed that the labeled material had moved to the position of laminaribiitol. The N spectrum of compound II is identical to that of reduced laminaritriose (Table 1). Theref compound II was identified as laminaritriitol. TABLE 1

¹³C NMR Chemical Shifts for Laminaritriitol, GlcNAc(βl-6)Glc, Compound I and Compound II in D₂O

Compound Ring C-1 C-2 C-3 C-4 C-5 C-6 NHCOCH3

Laminaritriitol C 62.11 72.89 78.71 70.88 70.29 62.91

C 103.10 73.35 84.35 68.45 76.13 60.86

C" 102.87 73.59 75.69 69.73 75.46 60.86

GlcNAc(fil-6)Glc C a 92.45 71.96 73.02 70.18 70.57 68.71 β 96.31 74.35 75.06 70.18 76.05 68.95

Ca 101.98

55.73 73.97 69.83 76.11 175.1 KC0) β 102.06 22.40(CH₃)

I C 62.03 72.83 79.37 70.83 70.25 62.83

C 103.09 73.33 84.17 68.35 75.97 60.83

C" 102.54 73.55 75.68 78.68 75.41 60.65

C" 101.55 55.69 74.62 69.83 74.35 60.21 23.35(CH₃)

II C 62.11 72.85 78.75 70.33 62.11 c 103.14 73.33 84.49 68.46 76.15 60.86

C" 102.91 73.60 75.72 69.73 75.46

Structure of Compound III (Peak C - Figure 1) Acid Hydrolysis

Acid hydrolysis of compound HI (Peak C - Figure 1) liberated glucose and sorbitol in 1.1: 1.0 ratio. See Figure 2. The molecular weight of the compound was as expected from the analysis (calculated 739.4; found 740). See Figure 3c.

β-Glucosidase Digestion A portion (10 pmol, 10,000 cpm) of compound III was evaporated to dry and dissolved in 30 μl of acetate buffer at pH 4.5, containing 10 μg of sweet almon glucosidase. After 16 hours of incubation at 37° C, the sample was analyzed by pa chromatography. Standards: Glc; 2, laminaribiitol; 3, sophoritol; 4, cellobiitol; gentiobiitol.

The material behaved on paper chromatography (Figure 8b) or HPAEC (res not shown) like laminaribiitol and could be distinguished from the 1→2, 1→4 and 1→6 isom On the basis of these data and by analogy with compounds I and II, compound HI identified as laminaribiitol.

Other Mixed Oligosaccharides Containing N-Acetylglucosamine and Glucose

Figure 9 illustrates a scheme for the generation of different oligosaccharides chitinase digestion. Chitinase is able to cut between a GlcNAc and a Glc residue, if linkage between the two sugars is β(l→4). Therefore, compounds I and II would be deri from chitin chains with an odd or even number of GlcNAc residues, respectively, b attached to a reduced laminaritriose. Similarly, Compound III would result from hydrol of an even-numbered chain linked to laminaribiitol. The corresponding oligosaccharide fr an odd-numbered chain (Figure 9, compound IV) should behave in the P-2 column eithe a reduced tetrasaccharide of glucose or as reduced diacetylchitobiose. Thus, it may have b hidden under the large peak of diacetylchitobiitol in Figure 1.

Accordingly, material from that peak was subjected to paper chromatograp Results are illustrated in Figure 10. This peak contained, in addition to the redu disaccharide, some slowly moving labeled material.

The slow-moving labeled band was excised and eluted with water. The standards were: laminaritriitol; 2, laminaribiitol; 3, diacetylchitobiitol; 4, glucitol.

Treatment of material separated from diacetylchitobiitol withβ- N-acetylglucosaminidase and/or β-glucosidase

The slow-moving band in the paper chromatogram of Figure 10 was eluted water, concentrated, and rechromatographed on a Bio-Gel P-2 column (1x90cm). Results illustrated in Figure 11a. Aliquots of the original material were subjected to incubation with ^β-N- acetylglucosaminidase, β-glucosidase, and both β-N-acetylglucosaminidase and β-glucosidase. Results are illustrated in Figure lib, c, and d, respectively. The standards were: 1, triacetylchitotriitol; 2, diacetychitobiitol; 3, laminaritriitol; 4, laminaribiitol; 5, glucitol; 6, glucose.

Treatment of the material with β-N-acetylglucosaminidase caused displacement of a large portion of the label to the elution position of either laminaribiitol or N- acetylglucosaminitol, whereas incubation with β-glucosidase had the same effect on a minor portion of the radioactive material. Finally, with a mixture of both enzymes, all of the radioactivity moved to the new position. The results are consistent with the hypothesis that the material eluted from paper contained a mixture of GlcNAc-β-Glc-β-Glc-ol (compound IV) and Glc-β-Glc-β-Glc-β-Glc-ol (compound V - Figure 9).

The isolation of compound V suggested that the corresponding compound VI (Figure 9) should also have been formed. According to its composition, this compound would be eluted in the P-2 column together with reduced triacetylchitotriose. Therefore, material from the reduced trisaccharide peak was analyzed by paper chromatography and found to contain a small amount of slower-moving labeled material (See Figure lla).

The slow moving radioactive material was eluted with water from paper, concentrated and treated with β-N-acetylglucosaminidase followed by Bio-Gel P-2 chromatography as described above. Results are illustrated in Figure 12b. The pentasaccharide was also incubated with β-glucosidase followed by Bio-Gel P-2 chromatography as described above. Results are illustrated in Figure 12c. The standards were: 1, triacetychitobiitol or laminarihexaitol; 2, laminaripentaitol; 3, diacetychitobiitol or laminaritetraitol; 4, laminaritriitol; 5, compound III or laminaribiitol; 6, glucose. This substance was resistant to β-glucosidase, but was digested by β-N- acetylglucosaminidase, with concomitant displacement to the laminaritetraitol position in the P-2 column. The substance had the expected properties of compound VI (GlcNAc-β-Glc-β- Glc-β-Glc-β-Glc-ol).

Glucose Oligosaccharides Do not Preexist in the Intact Cell Wall

The possibility remained that the glucose oligosaccharides attached to chitin preexisted as such in the intact cell wall before glucanase digestion, rather than being part of a larger chain. If the glucose oligosaccharides did pre-exist, they would be labeled i borotritide reduction were performed before, rather than after treatment with gluca Therefore, walls were reduced twice, before and after β(l→3) endoglucanase treatment were chromatographed on a Bio-Gel P-2 column. Results are illustrated in Figure 13a. standards were: 1, void volume; 2, triacetylchitotriitol; 3, laminaripentaitol; diacetychitobiitol; 5, laminaritriitol; 6, laminaribiitol; 7, glucitol; 8, glucose. Cell walls also reduced before β(l→3) endoglucanase treatment as described above. Results illustrated in Figure 13b.

Only the reduced chitooligosaccharide peaks, resulting from free chitin ch were labeled (Figure 13b). Accordingly, the oligosaccharides were part of an extended gl chain and can only be exposed to reduction by degradation of the chain with glucanase.

Synthesis of the Glucan-linked Chitin Requires Chitin Svnthetase 3

Three different chitin synthetases (Chsl , Chs2 and Chs3) participate in diffe aspects of chitin synthesis in yeast (Shaw et al. , J. Cell Biol , 114: 111-123, 1991; Cabi al., J. Cell. Biol , 108: 1665-1672, 1989). Mutants in each of the three synthetases available.

Wild type strain D3C cell walls were treated with endoglucanase, redu incubated with chitinase, and chromatographed on Bio-Gel P-2 columns as described ab Results are illustrated in Figure 14α. The standards were: 1 , void volume; triacetylchitotriitol; 3, diacetylchitobiitol; 4, diacetylchitobiose; 5, laminaritriitol; laminaribiitol; 7, GlcNAc; 8, Glc.

The procedure was repeated with Strain ECY 36-3C (chsl chs2:LEU2), St ECY36-3D (chsl call/csd2) (this strain is deficient in Chs3), and Strain ECY36-3D pH (the plasmid contains the CAL1/CSD2 gene and restores Chs3 activity).

Results are illustrated in Figures 14b, c, and d, respectively.

Strain ECY36-3C, with mutations in Chsl and Chs2, still showed a full a of oligosaccharides (Figure 14b), i.e. it is not impaired in the formation of chitin-gl chains. However, strain ECY36-3D, which lacked Chs 1 and Chs3, showed only the reduced chitooligosaccharide peaks, derived from free chitin (Figure 14c). Transformatio this strain with a plasmid carrying the CALIICSDI gene, required for Chs3 activity, rest a full complement of oligosaccharides (Figure I4d). Therefore, Chs3 is the synthetase involved in the formation of the chitin that becomes glucan-linked.

Tritium-labeled Void Volume Peak The material solubilized by glucanase and chitinase digestion was fractionated on P-2 columns. A fairly large amount of radioactivity emerged at the void volume (Figure 1). This material was rechromotographed on Sephacryl S-200 and Sephacryl S-300 columns. Results indicated that the material was heterogeneous and of high molecular weight, in the 200,000-300,000 dalton range. NMR spectra were similar to those of pustulan, a β(l→6)- linked glucan, although other components appeared to be present. Acid hydrolysis released glucose and some mannose.

The void volume material was barely detectable in the Chs3 mutant (Figure 14c) and was restored by the C i/CSD2plasmid (Figure I4d), which indicated that it was originally bound to chitin whose synthesis depends on the presence of Chs3. The void volume labeled material was also somewhat reduced in the chsl -chsl mutant (Figure 14b) as well as in the wild-type fraction resulting from cell walls reduced with borotritide before glucanase digestion (Figure 13b).

Example 1 illustrates that the oligosaccharides containing GlcNAc linked β(l→4) to glucose were not solubilized until cell walls were digested with both β-glucanase and chitinase. This indicates that the oligosaccharides originate in the linkage region of glucan and chitin. The presence of both N-acetylglucosamine and glucose in some of the compounds confirmed this. The short glucose chains were originally part of the glucan. because they are protected from reduction when the polysaccharide is intact.

The structure of compound I corresponds to an original oligosaccharide (before reduction) containing one N-acetylglucosaminyl group linked in β(l→4) to laminaritriose. Compound I and the other five compounds studied can be arranged in two homologous series, one containing 2, 3, or 4 β(l-3)-linked glucose units and the other with the same units plus an N-acetylglucosaminyl group at the non-reducing end. The different lengths of the glucose moieties was due to some variability in the position of the β(l→3) linkage hydrolyzed by the zymolyase preparation. The main activity in zymolyase appeared to be a β(l→3)endoglucanase that gives rise to laminaripentaose as the major product (Kitamura et al. , J. Gen. Appl. Microbiol. , 20:323-344, 1974). Therefore, the remaining stubs attached to chitin should not be much more than five glucose units long. The existence of chitin chains with an odd or e number of GlcNAc residues and the ability of Serratia exochitinase to hydrolyz GlcNAc(βl→4)Glc residue explain the presence or absence of GlcNAc.

The sum of reduced diacetylchitobiose and triacetylchitobiose is equivalen the number of free chitin chains. The sum of oligosaccharides should be equivalent to number of glucan-linked chains. This analysis suggests that between 40 and 50% of the c chains are engaged in linkage with glucan. The chitin to glucan ratio in the cell wall is a 1: 10 in strain D3C. The effect of small amounts of chitin on the solubilization in hot al of about 70% of the glucan (Mol et al., F.E.M.S. Microbiol. Lett. , 41:95-99, 1987) ma explained by the different chain lengths of chitin and glucan. The reported values are ~ for the former (Kang et al., J. Biol. Chem. , 259: 14966-14972, 1984) and ~ 1500 for the la (Manners et al., Biochem J , 135: 19-30, 1973; Fleet et al., J. GeΛz. Microbiol , 94: 180-1 1976). Thus, a relatively small number of chitin molecules may suffice to affect the proper of a 15-fold higher amount of glucan. The results above with chitin synthetase mutants indicate that Chs3 is enzyme responsible for the formation of the chitin that is incorporated into the chitin-β(l linked-hexose oligosaccharide. This is consistent because it is known that Chs3 is invol in the synthesis of 80-90% of the cell wall chitin, including that present in a ring at the of an emerging bud and that dispersed throughout the wall (Shaw et al. , J. Cell Bi 114: 111-123, 1991; Bulawa et al., P.N.A.S., USA, 87:7424-7428, 1990). This chiti incorporated into the cell wall late in the cell cycle, after cytokinesis and during maturation (Shaw et al.). Therefore, the glucan of the bud cell wall formed until that mo could not be bound to chitin and must represent an alkali-soluble glucan. This is suppo by the finding that soluble glucan is the precursor of insoluble glucan and that bud w disappear after prolonged alkali extraction. Thus, chitin is attached to preexisting glucan

It has been suggested that the chitin glucan bond may be formed in periplasmic space by transglycosylation from a newly-formed chitin chain (Cabib et Microbiol. Sci. , 5:370-375, 1988). According to this hypothesis, a portion of the chitin c would be released in the reaction. An alternative mechanism is possible if chitin chains g from reducing end, as does the O-antigen of Gram-negative bacteria (Robbins et al., Scie 158: 1536-1542, 1967). In that case, the GlcNAc residue at the reducing end would re activated during synthesis, and the whole nascent chain could be transferred directly to gluc Example 2 - An Enzymatic Assay for Chitin-Glucan Linkage

50 μl of chitin (10 mg/ml in PBS), 50 μl of ³H-glucan (prepared as in Example 1) (10⁴ cpm/mg, 10 mg/ml in PBS), and 10 μl of CGβ(l→4)T source are mixed. The mixture is incubated at 30°C for 1 hour. 5 μl of a solution of zymolyase 100T (7.5 mg/ml, prepared as in Example 1) are added, and the incubation is continued for 1 hour at 37°C. Subsequently, 200 μl of ice-cold 20% trichloroacetic acid is added, and the resultant mixture is incubated on ice for 5 minutes. Finally, the reaction mixture is filtered through Whatman GF/C filters. The radioactivity associated with the filters is then quantified by liquid scintillation counting. Controls are prepared either omitting the enzyme source or with 2 mg unlabelled glucan.

For a given sample, a dose-dependent increase in acid-precipitable radioactivity indicates the formation of a chitin-glucan linkage.

Example 3 - High-Throughput Screening for Inhibitors of Chitin-Glucan Linkage

The assay described in Example 2 is adapted for high-throughput screening as follows:

A known source of the enzyme is used, such that 50% of the ³H-glucan (i.e. 2500 cpm) is converted from an acid-soluble to acid-insoluble form during the reaction. Reaction mixtures are formed in 96-well microliter dishes according to the procedure of Example 2, with the addition of 15 μl of a solution containing test inhibitory compounds. After incubation at 30 °C for 1 hour, zymolyase 100T is added according to the procedure of Example 2 and incubation is continued for an additional hour.

Using automated equipment, the contents of each well are transferred to a sheet of Whatman 3MM filter paper. The paper is immersed in ice-cold 10% trichloroacetic acid for 10 minutes and is then washed in 5% trichloroacetic acid. Areas of the paper corresponding to each well are excised and counted. A reduction in the number of cpm detected in a given well indicates a candidate inhibitory compound.

Example 4 - Test of Antifungal Properties

A candidate antifungal agent is dissolved in a biologically acceptable solvent such as saline. Serial 10-fold dilutions of the agent are prepared in yeast growth medium. 10 ml aliquots of each dilution are inoculated with 10⁴ yeast cells, followed by incubatio 30°C. At hourly intervals, the growth of the cultures is ascertained by measuring absorbance at 600 nm.

An effective antifungal agent is one that suppresses the growth of yeast cells >90% at concentrations that are practical for agricultural or medicinal applications.

Example 5 - Antifungal Formulation for Agricultural Use

An antifungal formulation for agricultural use is prepared by mixing acetylglucosamine-3(l→4)-glucose with deionized water. The resultant composition is spra on a fungally infected plant.

Example 6 - Antifungal Formulation for Medicinal Use

An antifungal formulation suitable for animal use is prepared by mixing acetylglucosamine β(l→4)glucose with saline. The resultant solution is administe systemically to a mammal suffering from a fungal infection.

All patents, applications, articles, publications, and test methods mentio above are hereby incorporated by reference.

Many variations of the present invention will suggest themselves to those skil in the art in light of the above detailed description. Such obvious variations are within the intended scope of the appended claims.

Claims

IN THE CLAIMS: 1. An antifungal composition comprising: (a) an antifungal effective amount of (i) an oligosaccharide comprising an N-acetylhexosamine residue linked S(l→4) to a hexose, (ii) an inhibitor of an enzyme having as a first substrate, the terminal reducing N-acetylglucosamine residue of chitin and having as a second substrate the non-reducing glucose residues of (βl→3) linked glucans, said enzyme catalyzing the formation of a (βl→4) linkage between said N-acetylglucosamine and said glucose, or (iii) any combination thereof; and (b) a biologically acceptable carrier.

2. An antifungal composition as defined in claim 1. wherein said biologically acceptable carrier comprises a pharmaceutically acceptable carrier.

3. An antifungal composition as defined in claim 1 , wherein said N- acetylhexosamine of said oligosaccharise comprises N-acetylglucosamine and said hexose of said oligosaccharide comprises glucose.

4. An antifungal composition as defined in claim 1, wherein said oligosaccharide comprises a disaccharide.

5. An antifungal composition as defined in claim 1, wherein said enzyme inhibitor comprises N-acetylglucosamine modified at the 1 -carbon by a member selected from the group consisting of (CH₂)_n-OH wherein n is an integer from 1-12, C ₂ alkyl, aryl, aryl substituted with C,-C₁₀ alkyl or C_rC₁₀ alkenyl, and allosamizoline.

6. An antifungal composition as defined in claim 1, wherein said enzyme inhibitor comprises glucose modified at the 4-carbon by a member selected from the group consisting of (CH₂)_n-OH wherein n is an integer from 1-12, C ₂ alkyl, aryl. aryl substituted with C,-C₁₀ alkyl or C,-C₁₀ alkenyl, and allosamizoline.

7. An antifungal composition as defined in claim 5, wherein said 1 -ca modified N-acetylglucosamine is further modified at an additional carbon.

8. An isolated fungal enzyme, said enzyme having as a first substrat terminal reducing N-acetylglucosamine residue of chitin and having as a second substrat non-reducing glucose residues of /3(1→3) linked glucans, said enzyme catalyzing the form of a β(l→4) linkage between said N-acetylglucosamine and said glucose.

9. An enzyme as defined in claim 8, wherein said fungal species is sel from the group consisting of Saccharomyces cerevisiae, Candida albicans, Histopl capsulatum, Coccidioides immitis, Blastomyces dermatitidis, Cryptococcus neoformans, Aspergillus fumigatus .

10. An enzyme as defined in claim 9, wherein said fungal speci Saccharomyces cerevisiae.

11. An enzyme as defined in claim 9, wherein said fungal species is Can albicans.

12. A composition comprising an inhibitor of an enzyme as defined in c 8.

13. An antifungal composition as defined in claim 1, wherein biologically acceptable carrier comprises a pharmaceutically acceptable carrier.

14. A method of preventing fungal infection of a plant, said me comprising applying to said plant, a prophylactically effective amount of an antifu composition as defined in claim 1.

15. A method of preventing fungal infection in an animal, said me comprising administering to said animal, a prophylactically effective amount of an antifu composition as defined in claim 1.

16. A method as defined in claim 15, wherein said administration is performed by a mode selected from the group consisting of topical administration and systemic administration.

17. A method of treating a fungal infection in a plant in need of such treatment, said method comprising applying to said plant, a therapeutically effective amount of a composition as defined in claim 1.

18. A method of treating a fungal infection in an animal in need of such treatment, said method comprising administering to said mammal, a therapeutically effective amount of a composition as defined in claim 1.

19. A method as defined in claim 18, wherein said administration is performed by a mode selected from the group consisting of topical administration and systemic administration.

20. A method for screening for antifungal compounds, said method comprising (a) contacting said compound with an oligosaccharide comprising an N-acetylhexosamine residue linked β(l→4) to a hexose, and (b) detecting any free N-acetylhexose or free hexose.

21. A screening method for identifying antifungal compounds, said method comprising (a) contacting an enzyme as defined in claim 8 with an N- acetylhexosamine and a hexose in the presence of said compound, to form a test mixture; (b) contacting said enzyme with said N-acetylhexosamine and said hexose in the absence of said compound, to form a control mixture; (c) detecting any formation of a β(l→4) linkage between said N- acetylhexosamine and said hexose in said test mixture and in said control mixture; (d) comparing efficiency of said formation of said linkage in said test mixture and in said control mixture; and (e) selecting as an antifungal compound a test compound that ca a decrease in the efficiency of formation of said linkage in said test mixmre relative to efficiency of formation of said linkage in control said mixture.