US20200032308A1

US20200032308A1 - Fermentation process for producing monosaccharides in free form from nucleotide-activated sugars

Info

Publication number: US20200032308A1
Application number: US16/521,054
Authority: US
Inventors: Stefan Jennewein; Katja Parschat
Original assignee: Jennewein Biotechnologie GmbH
Current assignee: Chr Hansen HMO GmbH
Priority date: 2015-01-30
Filing date: 2019-07-24
Publication date: 2020-01-30
Also published as: KR20170106975A; JP7133924B2; EP3050973A1; US11066685B2; EP3250702A1; CN107278232A; RU2746739C1; KR102667836B1; JP2018503383A; RU2021100512A; US20180273996A1; WO2016120448A1; JP2021072805A; CN107278232B

Abstract

The present invention relates to a process for producing a monosaccharide, e.g. L-fucose, in free form using a microbial fermentation process. The used microorganism exhibits hydrolase activity on nucleotide-activated sugars and releases the monosaccharide in an unmodified free form. The free monosaccharide is retrieved from the supernatant of the cultivated microorganism.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 15/546,778, filed Jul. 27, 2017, which is a National Stage entry of International Application No. PCT/EP2016/051919, filed Jan. 29, 2016, which claims to European Patent Application No. 15153383.3, filed Jan. 30, 2015.

REFERENCE TO SEQUENCE LISTING SUBMITTED AS A COMPLIANT ASCII TEXT FILE (.txt)

Pursuant to the EFS-Web legal framework and 37 CFR §§ 1.821-825 (see MPEP § 2442.03(a)), a Sequence Listing in the form of an ASCII-compliant text file (entitled “Sequence_Listing_3000045-001001_ST25.txt” created on 18 Jul. 2019, and 19,783 bytes in size) is submitted concurrently with the instant application, and the entire contents of the Sequence Listing are incorporated herein by reference.

BACKGROUND

Field

The present invention relates to a microbial fermentation process for producing a monosaccharide of interest in free form from nucleotide-activated sugars.

Description of Related Art

Carbohydrates play roles in all forms of life by taking on vital roles in energy storage, structural function, signalling, information storage etc. For this task nature synthesizes several major monosaccharides like glucose, N-acetyl-glucosamine, mannose, N-acetyl-mannosamine, fructose, fucose, ribose, sialic acid, xylose etc. and several minor ones for more specialized applications, like for example D-allose.
L-fucose (6-deoxy-L-galactose) and fucosylated oligo-, and polysaccharides are of great interest for the chemical, cosmetic and pharmaceutical industry since they have high potential for nutritional and biomedical applications (Hauber, H.-P., Schulz, M., Pforte, A., Mack, P., Zabel, P. & Schumacher, U. (2008) Inhalation with fucose and galactose for treatment of Pseudomonas aeroginosa in cyctric fibrosis patients. Int. J. Med. Sci. 5, 371-376; Isnard, N., Bourles-Dagonet F., Robert, L. & Renard, G. (2005) Studies on corneal wound healing: Effects if fucose on iodine vapor-burnt rabbit corneas. Ophthalmologica 219, 324-333; Robert, L., Fodil-Bourahla, I., Bizbiz, L. & Robert, A. M. (2004) Effect of L-fucose and fucose-rich polysaccharides on elastin biosynthesis, in vivo and in vitro. Biomed. Pharmacother. 58, 123-128; Wild, M. K., Lühn, K., Marquardt, T. & Vestweber, D. (2002) Leukocyte adhesion deficiency II: therapy and genetic defect. Cells Tissues Organs 172, 161-173; Adam, E. C., Mitchell, B. S., Schumacher, D. U., Grant, G. & Schumacher, U. (1997) Pseudomonas aeruginosa II lectin stops human ciliary beating: therapeutic implications of fucose. Am. J. Respir. Care Med. 155, 2102-2104). They are known to have anti-inflammatory, anti-viral, and anti-tumor properties and also act as prebiotics. Due to the anti-aging effect L-fucose is also of interest for cosmetics (Isnard, N., Fodil-Bourathla, I., Robert A. M. & Robert, L. (2004) Pharmacology of skin aging. Stimulation of glycosaminoglycan biosynthesis by L-fucose and fucose rich polysaccharides, effect of in vitro aging of fibroblasts. Biomed. Pharmacother. 58, 202-204). In addition fucosylated derivatives are known for their antiallergic and emulsifying properties.
Whereas some monosaccharides can be obtained from nature in large amounts and at reasonable cost (e.g. glucose, N-acetylglucosamine, and fructose), most monosaccharides are rather scarce and can be found in nature only in small amounts, like for example L-fucose (6-deoxy-L-galactose).
For commercial production of monosaccharides, almost exclusively oligosaccharides obtained from nature are used as sources. These oligosaccharides are acid hydrolyzed and from the released monosaccharides the individual sugars are purified. Due to the high chemical similarity of the monosaccharides (mostly differing from each other only by the orientation of individual hydroxyl-groups) the separation of individual monosaccharides in pure form is rather laborious and costly.
L-fucose represents such a rare sugar, which is currently obtained via the hydrolysis of complex oligosaccharides, either from algae or bacterial origin. For the purification of individual monosaccharides from complex hydrolysates often noxious chemical have to be employed, like for example lead acetate and excessive amounts of organic solvents (Schweiger, R. G. (1966) Preparation of α-L-fucosides and L-fucose from fucoidan. U.S. Pat. No. 3,240,775). Therefore, the isolation of individual monosaccharides from a complex hydrolysate of oligosaccharides is challenging (due to the high chemical similarity of the individual monosaccharides released) and environmentally harmful (due to the excessive use of toxic chemicals, such a lead carbonate). Also the availability of oligosaccharides rich in a certain sugar can be rather restricted in nature and also highly variable due to seasonal changes. L-Fucose represents such a scare monosaccharide which is traditionally obtained by the acid hydrolysis of fucose-containing polysaccharides. Fucose is mainly derived from the polysaccharide fucoidan, a fucan monosulfate present in all common brown seaweeds comprising the families Fucaceae and Laminariaceae (Black, W. A. P (1954): The seasonal variation in the combined L-fucose content of the common british Laminariaceae and Fucaceae. J. Sci. Food Agric. 5, 445-448). Today, L-fucose is obtained in large quantities mainly by the collection of brown seaweed belonging to the family Fucaceae, which can be found world-wide but in high amounts at the European shores of the Atlantic Ocean. The large-scale harvest of brown seaweed from sea shores causes environmental concerns and is limited by environmental protection laws.
For example, JP 2000351790 discloses a method for extracting fucoidan and for obtaining and separating a fucose-containing oligosaccharide from the extracted fucoidan.
Besides the hydrolysis of fucoidan from brown-seaweed recently a patent publication showed that L-fucose can also be obtained via the hydrolysis of natural occurring L-fucose containing bacterial polysaccharides: WO 2012/034996 A1 discloses a strain belonging to the Enterobacteriaceae family, which strain is able to produce extracellular polysaccharides which contain L-fucose. For the production of L-fucose, the polysaccharides produced by the strain are recovered and subjected to hydrolysis, e.g. by treatment with sulphuric acid or trifluoroacetic acid.
WO 2014067696 A1 describes for the first time a process for production of L-fucose by using a recombinant microorganism that possesses a glycosyltransferase and a glycosidase which work together to synthesize L-fucose in a free form. This process needs two enzymes and an acceptor molecule. The glycosyltransferase catalyses the transfer of fucose from GDP-L-fucose to the acceptor, for example lactulose, to synthesize fucosyllactulose. The Fucosylated acceptor (e.g. Fucosyllactulose) is then hydrolysed by a glycosidase into the acceptor molecule and L-fucose. The acceptor is then again available for fucosylation by the employed fucosyltransferase. L-fucose is then liberated from the cell by export into the medium were it can be retrieved from the supernatant. By this means the feedback inhibition of the GDP-fucose pathway can be easily overcome and significant (several g/I) amounts of free L-fucose can be obtained by microbial fermentation.
Besides the extraction of L-fucose from poly- or oligosaccharide hydrolysates, several synthetic routes for L-fucose have been developed starting from other monosaccharides, like L-arabinose, D-galactose, L-rhamnose, D-mannose and D-glucose. With the most efficient synthetic route developed by Defraye et al (1984) starting from the rare monosaccharide L-rhamnose (Defaye, J., Gadelle, A. & Angyal, S. (1984) An efficient synthesis of L-fucose and L-(4-²H)fucose. Carbohydr. Res. 126, 165-169). Generally the yields of these chemical syntheses are often rather poor and involve several chemical steps. Besides involving several synthetic steps, extensive protection group chemistry has to be used for the chemical synthesis of L-fucose. In general, the large-scale chemical synthesis of monosaccharides have not proved economical viable in comparison to extraction of L-fucose from polysaccharides collected from nature.
Thus, currently, the preparation of any monosaccharide in pure form requires a significant effort in the purification of other monosaccharides away from the target monosaccharide, often involving large volumes of organic solvents and other noxious chemicals. As a consequence, the exclusive accumulation of a single desired monosaccharide, like for example L-fucose, would be of immense help. However most microorganisms are restricted in the kinds of monosaccharides they are able to utilize. In addition, they often exert strong preferences towards certain monosaccharides in case that several monosaccharides are available at the same time as carbon source.

SUMMARY

In view of the above, it is an object of the present invention to provide a new process for the production of a single desired monosaccharide in free form, by means of which the monosaccharide can be retrieved fast and efficiently, i.e. in large scale and cost-effectively and without negative environmentally effects.
This and other objects are achieved by a process for producing, in large scale, a monosaccharide of interest in free form using a microorganism, the process comprising the steps of:
a.) providing a microorganism for the synthesis of the monosaccharide comprising an enzyme capable of catalyzing the hydrolysis of a nucleotide-activated monosaccharide to release the monosaccharide of interest from the nucleotide-activated monosaccharide, and
b.) cultivating the microorganism in a medium suitable for growing the microorganism, wherein the microorganism is unable to metabolize the monosaccharide to a significant extent, so that the monosaccharide of interest is produced and accumulates during cultivation step in free form.
The object underlying the invention is completely solved in this way.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Applicant's above process has not previously been described, utilizes a microorganism comprising and expressing an enzyme that hydrolyses a nucleotide-activated monosaccharide and accumulates the free monosaccharide. The enzyme possessing hydrolysing activity on nucleotide-activated sugars can be, e.g., a fucosyltransferase, preferably a variant of the alpha-1,2-fucosyltransferase encoded by the wbgL gene of E. coli:O126 (acc. No. ADN43847) or the 1,2-fucosyltransferase futC from Helicobacter pylori (acc. No. AAD29868). Although unmodified microorganisms having the above described enzymatically features can be employed within the present invention, according to one aspect of the invention, the microorganism is a recombinant microorganism, wherein the recombinant microorganism has been transformed to comprise and express at least one nucleic acid sequence not naturally occurring in the microorganism and encoding an enzyme capable of catalyzing the hydrolysis of a nucleotide-activated monosaccharide.
In contrast to prior processes, a single enzyme capable of catalyzing the hydrolysis of, i.e. hydrolyzing, nucleotide-activated sugars, i.e. monosaccharides, is used to release the monosaccharide, whereas previous processes known in the art, employ at least one enzyme transferring the monosaccharide from a donor substrate to an acceptor substrate with a subsequent step of releasing the monosaccharide from the acceptor by means of a glycosidase. This step is not necessary in the present invention thereby facilitating the process for producing a monosaccharide of interest. Accordingly, in the process according to the invention, an enzyme is used that is capable of catalyzing the hydrolysis of nucleotide-activated monosaccharides and releasing the monosaccharide in free form “in the absence of an acceptor”. Also, according to the invention, the process according to the invention is run without the targeted use of a glycosidase capable for releasing the monosaccharide from an acceptor-substrate.
With the newly provided process and the newly provided microorganism—recombinant or not—, it is possible to produce a desired monosaccharide in a free form and in large amounts, without necessitating chemicals or elaborate process steps. The process according to the invention represents a microbial fermentation process, suitable for getting employed for industrial large scale production of rare or other monosaccharides, which can be readily retrieved from the medium the microorganism is cultivated in.
The expression “monosaccharide” as used herein and as generally understood in the field of the invention, refers to the most basic unit of carbohydrates. Monosaccharides are the simplest form of sugar and are usually colourless, water-soluble, crystalline solids. Examples of monosaccharides include glucose, fructose, galactose, xylose, mannose, fucose, rhamnose and ribose. Monosaccharides are the building blocks of disaccharides such as sucrose and polysaccharides such as cellulose and starch. “Oligosaccharide” as the term is used herein and as generally understood in the state of the art, refers to a saccharide polymer containing two monosaccharides or more.
The term “nucleic acid sequence encoding . . . ” generally refers to any polyribonucleotide or polydeoxyribonucleotide, which may be unmodified RNA or DNA or modified RNA or DNA, and generally represents a gene which encodes a certain polypeptide or protein. The term includes, without limitation, single- and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions or single-, double- and triple-stranded regions, single- and double-stranded RNA, and RNA that is mixture of single- and double-stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded, or triple-stranded regions, or a mixture of single- and double-stranded regions. The term also encompasses polynucleotides that include a single continuous region or discontinuous regions encoding the polypeptide (for example, interrupted by integrated phage or an insertion sequence or editing) together with additional regions that also may contain coding and/or non-coding sequences.
In this context, the term “polypeptide(s)” refers to any peptide or protein comprising two or more amino acids joined to each other by peptide bonds or modified peptide bonds. “Polypeptide(s)” refers to both short chains, commonly referred to as peptides, oligopeptides and oligomers and to longer chains generally referred to as proteins. Polypeptides may contain amino acids other than the 20 gene encoded amino acids. “Polypeptide(s)” include those modified either by natural processes, such as processing and other post-translational modifications, but also by chemical modification techniques. It will be appreciated that the same type of modification may be present in the same or varying degree at several sites in a given polypeptide, without essentially altering the activity of the polypeptide. Also, a given polypeptide may contain many types of modifications. Modifications can occur anywhere in a polypeptide, including the peptide backbone, the amino acid side-chains, and the amino or carboxyl termini.
In the present invention the term “nucleotide-activated monosaccharide” used in combination with the “enyzme capable of catalyzing the hydrolysis of a nucleotide-activated monosaccharide”, or “enzyme capable of hydrolysing a nucleotide-activated monosaccharide”, describes an enzyme possessing catalytic activity on nucleotide-activated monosaccharides; hydrolysis leads to release of the desired monosaccharide. In this connection, the term “glycosyltransferase” designates and encompasses enzymes that catalyse the transfer of monosaccharide moieties from an activated nucleotide monosaccharide (the “glycosyl donor”) to a glycosyl acceptor molecule. In the present invention, the glycosyltransferase used in the process and microorganism according to the invention does calatyze the hydrolysis of the nucleotide-activated monosaccharide in absence of the acceptor molecule. According to one aspect of the invention, it is particularly preferred if the nucleotide-activated sugar hydrolase is a bacterial fucosyltransferase, and preferably a variant of the alpha-1,2-fucosyltransferase encoded by the wbgL gene of E. coli:0126 (acc. No. ADN43847) or other fucosyltransferases catalysing hydrolysis of GDP-L-fucose in the absence of an acceptor molecule.
Accordingly, the term nucleotide-activated sugar hydrolase or a nucleic acid/polynucleotide encoding an nucleotide-activated sugar hydrolase refer to an enzyme that catalyses hydrolytic cleavage of nucleotide-activated sugars, such as GDP-fucose, UDP-galactose, GDP-mannose, GDP-rhamnose, and other nucleotide sugars naturally occurring. Preferably this nucleotide-activated sugar hydrolase is a glycosyltransferase that does not or predominantly not transfer the monosaccharide to an acceptor molecule. In the case of GDP-L-fucose, the enzyme capable of hydrolyzing a nucleotide-activated monosaccharide is a fucosyltransferase, e.g. but not limited to, a alpha-1,2-fucosyltransferase.
More specific, it is preferred if the alpha-1,2-fucosyltransferase WbgL from E. coli:126 possessing the amino acid residues substitutions asparagine 69 to serine, histidine 124 to alanine, glutamate 215 to glycine, and isoleucine 268 to proline, or the 1,2-fucosyltransferase FutC from Helicobacter pylori or other fucosyltransferases exhibiting hydrolytic activity on GDP-L-fucose in the absence of an acceptor molecule is used.
Within the scope of the present invention, also nucleic acid/polynucleotide and polypeptide polymorphic variants, alleles, mutants, and interspecies homologs are comprised by those terms, that have an amino acid sequence that has greater than about 60% amino acid sequence identity, 65%, 70%, 75%, 80%, 85%, 90%, preferably 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or greater amino acid sequence identity, preferably over a region of at least about 25, 50, 100, 200, or 300, or more amino acids, to the amino acid sequences of the alpha-1,2-fucosyltransferases encoded by the wbgL gene of E. coli:O126 (acc. No. ADN43847) or futC of H. pylori (acc. No. AAD29868).
Additionally, the polypeptide of the hydrolysing enzyme may be altered by additions or deletions of peptide sequences in order to modify its activity. For example, polypeptide sequences may be fused to the enzymes polypeptide in order to effectuate additional enzymatic activity.
In addition, genes encoding an enzyme capable of hydrolyzing a nucleotide-activated monosaccharide may be altered so that the gene products include proteins or polypeptides that represent functionally equivalent gene products. Such an equivalent hydrolase gene product may contain deletions, additions or substitutions of amino acid residues within the amino acid sequence encoded by the hydrolase gene sequence described above, but which results in a silent change, thus producing a functionally equivalent gene product coding for an enzyme capable of hydrolyzing a nucleotide-activated monosaccharide. Amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipathic nature of the residues involved. For example, nonpolar (hydrophobic) amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan, and methionine; planar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine, and glutamine; positively charged (basic) amino acids include arginine, lysine, and histidine; and negatively charged (acidic) amino acids include aspartic acid and glutamic acid.
Within the context of this invention, “functionally equivalent”, as used herein, refers to a polypeptide capable of exhibiting a substantially similar in vivo hydrolase activity on nucleotide-activated sugars as the endogenous hydrolase gene product encoded by the hydrolase gene sequence described above, as judged by any of a number of criteria, including but not limited to antigenicity, i.e., the ability to bind to an anti-nucleotide-activated sugar hydrolase antibody, immunogenicity, i.e., the ability to generate an antibody which is capable of binding a nucleotide-activated monosaccharide hydro-laseprotein or polypeptide, as well as enzymatic activity. Accordingly, the present invention also comprises enzymes that are functionally equivalent to the ones specifically disclosed.
Also, one skilled in the art will readily derive from the present invention, that any modification to the disclosed enzymes can be used within the process and microorganism of the present invention, which modification is leading to an increased hydrolysing activity of the described enzymes herein. Thus, such modified enzymes displaying an increased hydrolysing activity compared to the unmodified form are comprised by the invention as well.
Included within the scope of the invention are nucleotide-activated sugar hydrolase proteins, polypeptides, and derivatives (including fragments) which are differentially modified during or after translation. Furthermore, non-classical amino acids or chemical amino acid analogs can be introduced as a substitution or addition into the enzymes polypeptide sequence.
According to a preferred embodiment of the process according to the invention, the enzyme is a variant of the 2-fucosyltransferase encoded by the wbgL gene, or a variant of the 1,2-fucosyltransferase encoded by the futC gene from Helicobacter pylori, the variant carrying at least one, preferably at least two, and more preferably more than two modifications as compared to the wild type 2-fucosyltransferase encoded by the wbgL gene or to the wild type 1,2-fucosyltransferase encoded by the futC gene, respectively, the modification leading to an increased hydrolizing activity of the enzyme.
The enzyme capable of hydrolyzing nucleotide-activated sugars may be produced by recombinant DNA technology using techniques well known in the art. Methods which are well known to those skilled in the art can be used to construct expression vectors containing enzyme coding sequences and appropriate transcriptional translational control signals that permit synthesis of an enzyme catalysing hydrolysis of nucleotide-activated sugars. These methods include, for example, in vitro recombinant DNA techniques, synthetic techniques, and in vivo genetic recombination. See, for example, the techniques described in Sambrook, J. and Russell D. W. (1989) Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.
According to an embodiment of the process according to the invention the at least one modification is at least one an amino acid substitution. According to another embodiment, the modification is or comprises at least one, two or more than two, in particular three, four, five, six, seven, eight, nine, or ten amino acids substitutions, wherein the modified enzyme capable of hydrolyzing a nucleotide-activated monosaccharide has an increased hydrolyzing activity on the nucleotide-activated monosaccharide compared to the unmodified wild-type enzyme.
According to one embodiment, it is preferred if the alpha-1,2-fucosyltransferase WbgL from E. coli:126 possessing the amino acid residues substitutions asparagine 69 to serine, histidine 124 to alanine, glutamate 215 to glycine, and isoleucine 268 to proline, or the 1,2-fucosyltransferase FutC from Helicobacter pylori or other fucosyltransferases exhibiting hydrolytic activity on GDP-L-fucose in the absence of an acceptor molecule is used.
One skilled in the art will appreciate from the disclosure of this invention, that not only the specific substitutions as specified above, but also other modifications of these specifically described enzymes, in particular other substitutions are encompassed by this invention, as long as the accordingly modified enzyme has an increased hydrolyzing activity on the nucleotide-activated monosaccharide compared to the unmodified wild-type enzyme. Alternative substitutions, which can be suitable, are also discussed above more generally, but should be applied here also.
Presently, and throughout the invention, “recombinant” means genetically engineered DNA prepared by transplanting or splicing genes from one species into the cells of a host microorganism of a different species. Such DNA becomes part of the host's genetic makeup and is replicated.
“Microorganism” presently designates and encompasses any microscopic organism that comprises either a single cell, cell clusters, or multicellular relatively complex organisms, which is suitable to be employed in the process according to the invention, and particularly includes bacteria and yeast. A microorganism as employed according to the invention can be cultivated in a liquid medium, and generally needs a carbon source in the medium to grow and replicate.
Consequently, “a recombinant host microorganism” is designated to mean any microorganism containing, a nucleic acid sequences coding for a glycosyltransferase or nucleotide-activated sugar hydrolase, or coding for a fucosyltransferase or a GDP-L-fucose hydrolase, wherein the nucleic acid sequences coding for these enzymes are nucleic acid sequences foreign to/not naturally occurring in the recombinant (host) cell and wherein the foreign/not naturally in said microorganism occurring sequence is integrated in the genome of the host microorganism cell. Thereby, “not naturally occurring” means that the nucleic acid sequence is foreign to said host microorganism cell, i.e. the nucleic acid sequences are heterologous with respect to the microorganism host cell. The heterologous sequence may be stably introduced, e.g. by transfection, transformation, or transduction, into the genome of the host microorganism cell, wherein techniques may be applied which will depend on the host cell the sequence is to be introduced. Various techniques are known to a person skilled in the art and are, e.g., disclosed in Sambrook et al., 1989, supra. Thus, the host cell the heterologous sequence has been introduced in, will produce the heterologous proteins the nucleic acid sequences according to the invention are coding for.
For recombinant production, host cells can be genetically engineered to incorporate expression systems or portions thereof and the nucleic acid sequences of the invention. Introduction of a nucleic acid sequence into the host microorganism cell can be effected by methods described in many standard laboratory manuals, such as Davis et al., Basic Methods in Molecular Biology, (1986), and Sambrook et al., 1989, supra.
Thus, the nucleic acid sequences according to the invention, may, e.g., be comprised in a vector which is to be stably transformed/transfected into host microorganism cells.
A great variety of expression systems can be used to produce the polypeptides of the invention. Such vectors include, among others, chromosomal, episomal and virus-derived vectors, e.g., vectors derived from bacterial plasmids, from bacteriophage, from transposons, from yeast episomes, from insertion elements, from yeast chromosomal elements, from viruses, and vectors derived from combinations thereof, such as those derived from plasmid and bacteriophage genetic elements, such as cosmids and phagemids. The expression system constructs may contain control regions that regulate as well as engender expression. Generally, any system or vector suitable to maintain, propagate or express polynucleotides and to synthesise a polypeptide in a host may be used for expression in this regard. The appropriate DNA sequence may be inserted into the expression system by any of a variety of well-known and routine techniques, such as, for example, those set forth in Sambrook et al., supra.
As used herein, the term “recovering” means isolating, harvesting, collecting or otherwise separating from the microorganism culture the monosaccharide produced by the microorganism according to the invention.
According to a preferred embodiment of the process according to the invention, the microorganism is further modified to have inactivated or severely reduced or to lack catabolic pathways leading to the degradation of the produced monosaccharide.
According to yet another embodiment, the microorganism is further modified to have inactivated or severely reduced or to lack genes involved in the catabolism of L-fucose.
According to another embodiment, the microorganism is further modified to overexpress at least one gene involved in the biosynthesis of the nucleotide-activated monosaccharide to improve supply of the nucleotide-activated monosaccharide of the monosaccharide. In this regard it is preferred if the at least one gene is heterologous or homologous.
According to another embodiment of the process according to the present invention, at least one gene involved in the biosynthesis of GDP-fucose, GDP-mannose or GDP-rhamnose is overexpressed to improve supply of GDP-fucose, GDP-mannose or GDP-rhamnose, respectively. In this regard it is preferred if the at least one gene is heterologous or homologous.
According to another embodiment of the process according to the present invention, the microorganism is further modified to have inactivated or reduced competing pathways for the nucleotide-activated monosaccharide.
According to another embodiment of the process according to the present invention, the microorganism is further modified to express a phosphatase, in case where the monosaccharide is released in a phosphorylated form by the enzyme.
Throughout the invention, it is particularly preferred if the free monosaccharide to be produced is selected from L-fucose, L-rhamnose or L-mannose.
In a preferred embodiment, the microorganism is cultivated in a medium containing a carbon source that is selected from glycerol, sucrose, acetate, glucose, fructose, molasses, lactose, xylose, cellulose, syngas, carbon dioxide or carbon monoxide. In this context it is to be understood that any other—preferably low-cost—fermentation substrates can be employed as carbon source, and the person skilled in the art will readily able to employ a carbon source suitable within the present invention in order to grow the microorganism to produce the desired monosaccharide in large-scale.
According to one aspect of the invention, a carbon source is constantly added to the medium during the cultivating step of the microorganism, e.g. a recombinant microorganism.
By constantly adding the carbon source during the cultivation step, a constant and effective production of the monosaccharide is accomplished.
According to another aspect of the invention, the monosaccharide is recovered from supernatant of the cultivated recombinant host microorganism, which supernatant is obtained by centrifuging the cultivated host microorganism to obtain a supernatant and a host microorganism pellet.
With the newly provided process, it is possible to retrieve the produced monosaccharide from the medium the host microorganism is cultivated in, since the monosaccharide which is produced in a microorganism cell is transported into the medium, thus making it effortlessly possible to recover the monosaccharide from the supernatant, once the cells of the microorganism have been separated from the cultivation medium.
Other mono-, or oligosaccharides which may be produced in the microorganism during the synthesis of the desired the monosaccharide, and which mono-, or oligosaccharides impair/interfere with the recovering/purification step of the desired monosaccharide, can be metabolised by the microorganism, so that the recovering step of the desired monosaccharide is further improved and facilitated. Therefore saccharide metabolising enzyme(s)) may be externally added/supplied to the medium at the end of the process according to the invention. In doing so, undesired sugars cannot accumulate and do not interfere with the recovering of the desired monosaccharide. Genes encoding metabolic pathways or enzymes can be expressed in the microorganism in order to metabolize otherwise interfering undesired monosaccharides, and one skilled in the art will—upon reading the invention—readily recognize other suitable pathways or enzymes to deregulate/activate or supply, which will depend from the monosaccharide to be produced.
According to another aspect of the invention, the process according to the invention comprises the following steps:

- a) providing, in a medium suitable for growing a microorganism, a recombinant host microorganism which has been transformed to comprise a nucleic acid sequence encoding an enzyme catalysing hydrolysis of nucleotide-activated monosaccharide not naturally occurring in the microorganism wherein the microorganism is unable to metabolize the monosaccharide to be produced in significant amounts,
- b) cultivating the recombinant host microorganism in said medium whereby the monosaccharide is produced in a free form,
- c) recovering the free monosaccharide from the medium.

Thus, the process as described in the above paragraphs comprises the additional step of recovering the free monosaccharide from the medium.
According to another aspect of the invention, there is disclosed and claimed a microorganism
The definitions used and set forth above for specific terms in connection with the process do also apply for the recombinant microorganism presented therein.
According to a preferred embodiment, the microorganism—used in the process according to the invention and claimed therein—is selected from a bacterial or yeast strain able synthesize nucleotide-activated sugars from which the desired monosaccharide can be obtained by hydrolytic cleavage of the nucleotide-activated monosaccharide. The bacterium Escherichia coli, Corynebacterium glutamicum and the yeast Saccharomyces sp. have the advantage that these microorganisms can be grown easily and inexpensively in laboratory settings, and the bacterium and yeast have been intensively investigated for over many years.
Accordingly, in a preferred embodiment, the host microorganism used in the process according to the invention and otherwise claimed therein is selected from the group consisting of bacteria and yeast, and is preferably an Escherichia coli strain.
It is further preferred in an embodiment of the present invention, if the recombinant host microorganism is further modified to lack genes coding for enzymes involved in the metabolism of the desired monosaccharide, in the case of L-fucose as desired monosaccharide genes encoding L-fuculosose kinase, L-fucose isomerase, fuculose-1-phospate aldolase, and UDP-glucose:undecaprenyl-phosphate glucose phosphotransferase. In addition, and according to a preferred embodiment, glycosyltransferase genes using the nucleotide-activated monosaccharide as substrate for the synthesis of polysaccharides (e.g. fucosyltransferases, or enzymes involved in the synthesis of fucosylated oligosaccharides such as colonic acid) are deleted.
Additionally, overexpression of genes improving synthesis of nucleotide-activated sugars is preferred. In the case of GDP-L-fucose genes encoding phosphomannomutase (mane), mannose-1-phosphate guanosyltransferase (manC), GDP-mannose-4,6-dehydratase (gmd), and GDP-L-fucose synthase (wcaG) from E. coli or adequate genes from other organisms are overexpressed in the respective microorganism.
This embodiment has the advantage that intracellular degradation of the produced monosaccharide L-fucose and production of colonic acid is prevented and synthesis of GDP-L-fucose is improved.
In another preferred embodiment, the recombinant host microorganism is further transformed to contain genes enabling the recombinant host microorganism to grow on sucrose or glycerol as sole carbon source, and it is particularly preferred if the csc-gene cluster of Escherichia coli W (acc. No. CP0021851) is integrated into the genome of the host microorganism, which gene cluster comprises the genes sucrose permase, fructokinase, sucrose hydrolase, and a transcriptional repressor (genes cscB, cscK, cscA, and cscR, respectively), that enable the transformed microorganism to grow on sucrose as sole carbon source.
In this connection it is noted that the embodiments listed as preferred for the process according to the invention all do apply for the claimed microorganism, where applicable.
Accordingly, the present invention also relates to the use of a microorganism possessing an enzyme catalysing the hydrolysis of nucleotide-activated monosaccharide wherein the microorganism is unable to metabolize the monosaccharide, and the invention further relates to the use of the recombinant microorganism according to the invention for the production of a monosaccharide, in particular of L-fucose.
It is noted that the definitions set forth above for describing certain terms of the process according to the invention shall apply for the microorganism, recombinant or unmodified, as claimed and described herein.
Alternatively, the method for producing monosaccharides may be applied on cell-free systems, whereby the enzyme according to the invention and suitable substrates are mixed in an aqueous reaction medium. The enzyme can be utilized free in solution, or they can be bound or immobilized to a support such as a polymer and the substrate may be added to the support. The support may be, e.g., packed in a column.
In particular, the present invention relates to a process wherein a recombinant Escherichia coli strain is used as recombinant host microorganism, wherein in the recombinant Escherichia coli strain the L-fucose isomerase gene, the L-fuculose kinase gene, and the UDP-glucose:undecaprenyl-phosphate glucose phosphotransferase have been deleted, and wherein the recombinant Escherichia coli strain has been transformed to comprise a) genes enabling the E. coli strain to grow on sucrose or glycerol as sole carbon source, the genes encoding, respectively, sucrose permase, fructokinase, sucrose hydrolase, and a transcriptional repressor, b) genes encoding phosphomannomutase, mannose-1-phosphate guanosyltransferase, GDP-mannose-4,6-dehydratase, and GDP-L-fucose synthase from E. coli or other organisms, c) a gene encoding an enzyme catalysing hydrolysis of nucleotide-activated monosaccharides, e.g. a fucosyltransferase that hydrolyses GDP-L-fucose in absence of an acceptor molecule. Further advantages follow from the description of the embodiments and the attached drawings.
It goes without saying that the abovementioned features and the features which are still to be explained below can be used not only in the respectively specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention. Also, it is noted that the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims.

FIGURES

Several embodiments of the invention are illustrated in the figures and explained in more detail in the following description. In the figures:

FIG. 1 Detection of free L-fucose in the culture supernatant of an E. coli BL21(DE3) production strain containing a pDEST:wbgL library after random mutagenesis of wbgL by error-prone PCR. Supernatants of cultures from E. coli BL21(DE3) production strain harboring pDEST:wbgL(error-prone) clones were applied to a colorimetric L-fucose dehydrogenase assay (for description of the assay see paragraph [0089] below). Well depicted as “WT” contained supernatant of an E. coli BL21(DE3) production strain pDEST:wbgL culture, expressing the unmodified wbgL gene. Wells signed “D1” and “H2” contained culture supernatant from clones synthesizing WbgL variants (H124A E215G) (clone D1) and WbgL (N69S I268P) (clone H2);

FIG. 2 LC-MS/MS analytics of culture supernatants of E. coli BL21(DE3) production strain harboring pDEST:wbgL(H124A E215G) (clone D1), and pDEST:wbgL(N69S I268P) (clone H2). 4.3 g/L, and 2.5 g/L L-fucose were produced by clones D1, and clone H2, respectively;

FIG. 3 Detection of L-fucose released from GDP-L-fucose by GDPL-fucose hydrolase activity. Cell lysates of E. coli BL21(DE3) pDEST:futC and E. coli BL21(DE3) pDEST:wbgL (H124A E215G) were applied to an in vitro GDP-L-fucose hydrolase assays containing 5 mM GDP-L-fucose. Free L-fucose was detected in a colorimetric L-fucose dehydrogenase assay (for description of the assay see paragraph [0089] below). The assay in well 1 contained 0.27 units FutC, in well 2 0.32 units WbgL (H124A E215G) were applied. To confirm stability of GDP-L-fucose the assay was performed with bovine serum albumin (well 3); and

FIGS. 4A-D The sequence of <P1e1-manCB-PT₅-gmd> (SEQ ID No: 1), wcaG-dhfr (FIG. 4A), <cscB-cscK-cscA-cscR> (SEQ ID No. 2) (FIG. 4B), <wbgL> (SEQ ID No. 3) (FIG. 4C), and <futC> (SEQ ID No. 4) (FIG. 4D).

EXAMPLES

Construction of a Fucose Producing E. coli Strain
Escherichia coli BL21 (DE3) (Novagen, Darmstadt, Germany) was used for genetic manipulations to construct the fucose production strain. Since fucose is produced by hydrolysis of GDP-L-fucose, synthesis of GDP-L-fucose is enhanced by genomic integration and overexpression of the genes encoding phosphomannomutase (manB), mannose-1-phosphate guanosyltransferase (manC), GDP-mannose-4,6-dehydratase (gmd), and GDP-L-fucose synthase (wcaG) from E. coli K12 DH5α. The operon manC-manB is under transcriptional control of the P_tetpromotor and the operon gmd-wcaG is expressed from the P_T5promotor. The gene cluster <P_tet-manCB-P_T5-gmd, wcaG-dhfr> (SEQ ID No. 1; FIG. 4A) comprises also the dhfr gene, encoding a dihydrofolate reductase that confers trimethoprim resistance to the integrants. For integration of the cluster into the E. coli BL21(DE3) genome by transposition, the cluster is flanked by inverted terminal repeats specifically recognized by the mariner-family transposable element Himar1. In addition the csc-gene cluster of E. coli W was introduced into the genome of the host organism. The gene cluster comprises the genes for sucrose permease (cscB), fructokinase (cscK), sucrose hydrolase (cscA), and a transcriptional repressor (cscR). Integration of the cluster <cscB-cscK-cscA-cscR> (SEQ ID No. 2; FIG. 4B) that was flanked by Himar1 specific inverted terminal repeats was performed by Himar1 transposition and mediates to the host organism the ability to grow on sucrose as sole carbon source (Choi, K.-H. and Kim, K.-J. (2009) Applications of transposon-based gene delivery system in bacteria. J. Microbiol. Biotechnol. 19, 217-228).
To prevent GDP-L-fucose depletion by formation of colonic acid the gene wcaJ predicted to encode a UDP-glucose:undecaprenyl phosphate glucose-1-phosphate transferase was deleted from the E. coli BL21(DE3) genome according to the method of Datsenko and Warner (Datsenko, K. A. and Warner B. L. (2000) One-step inactivation of chromosomal genes in Escherichia coli K-12 using PCR products. Proc. Natl. Acad. Sci. USA 97, 6640-6645). The UDP-glucose:undecaprenyl phosphate glucose-1-phosphate transferase catalyzes the first step in colonic acid synthesis (Stevenson, G., Andrianopoulos, K., Hobbs, M. and Reeves, P. R. (1996) Organization of the Escherichia coli K-12 gene cluster responsible for production of the extracellular polysaccharide colonic acid. J. Bacteriol. 178, 4885-4893). Additionally, the genes fucI and fucK of the fucose catabolic pathway, encoding the fucose isomerase and fuculose kinase, respectively, were inactivated by genomic knock-out to inhibit degradation of L-fucose.
Cloning of the 2-Fucosyltransferases Genes wbgL and futC, and Mutagenesis of wbgL
The 2-fucosyltransferase gene wbgL (SEQ ID No. 3; FIG. 4C) from E. coli:0126 (acc. No. AND43847) was codon-optimized and prepared synthetically by GenScript Cooperation (Piscataway, USA). Also the futC (SEQ ID No. 4, FIG. 4D) gene encoding 1,2-fucosyltransferase from Helicobacter pylori (acc. No. AAD29868) was synthetically synthesized and codon optimized for expression in E. coli. For cloning into the vector pDEST14 the genes were amplified using primers 6128 (SEQ ID No. 5) and 6129 (SEQ ID No. 6) for wbgL, and primers 6195 (SEQ ID No. 7) and 6196 (SEQ ID No. 8) for futC, respectively; for primer sequences see table 1 below:

TABLE 1

List of oligonucleotides used for polymerase
chain reaction

primer	Sequence 5′-3′

6128	GGGGACAAGTTTGTACAAAAAAGCAGGCTTCGAAGGAGATACA
	ACATGGGCAGCATTATTCGTCTGCAGGGTGG (SEQ ID
	No. 5)

6129	GGGGACCACTTTGTACAAGAAAGCTGGGTTTAGCAGCTGCTAT
	GTTTATCAACGTTGATC (SEQ ID No. 6)

6195	GGGGACAAGTTTGTACAAAAAAGCAGGCTTCGAAGGAGGTAGA
	ACATGGCCTTTAAAGTGGTTCAGATCTGCGGC (SEQ ID
	No. 7)

6196	GGGGACCACTTTGTACAAGAAAGCTGGGTCCTATTACGCGTTA
	TATTTCTGAGATTTCACTTCG (SEQ ID No. 8)

Mutations in the wbgL gene were introduced by several rounds of error-prone PCR using the Diversify® PCR Random Mutagenesis Kit (Clonetech, Mountain View, USA) according to the manufactures instructions and primers 6128 and 6129. Purified error-prone PCR products were cloned into vector pDEST14 yielding pDEST:wbgL(error-prone). Cloning into vector pDEST14 was generally performed using the Gateway technology (Gateway® Technology manual (Life Technologies, Carlsbad, USA)). Sequencing of the plasmids was performed by LGC Genomics (Berlin, Germany). Recombinant plasmids were transformed in suitable E. coli hosts by electroporation.
Growth Media and Cell Cultivation
The E. coli BL21(DE3) production strain harboring the pDEST:wbgL(error-prone) plasmid library was grown in mineral salts medium with 1% (v/v) glycerol and 1% (v/v) sucrose as carbon sources. The medium consists of 2 g/L NH₄H₂PO₄, 7 g/L K₂HPO₄, 2 g/L KOH, 0.3 g/L citric acid, 0.98 g/L MgSO₄×7 H₂O, and 0.02 g/L CaCl₂×6 H₂O. It is supplemented with one milliliter per liter trace element solution (54.4 g/L ammonium ferric citrate, 9.8 g/L MnCl₂×4 H₂O, 1.6 g/L CoCl₂×6 H₂O, 1 g/L CuCl₂×2 H₂O, 1.9 g/L H₃BO₃, 9 g/L ZnSO₄×7 H₂O, 1.1 g/L Na₂MoO₄×2 H₂O, 1.5 g/L Na₂SeO₃, 1.5 g/L NiSO₄×6 H₂O). For selection 10 μg/mL trimethoprim and 100 μg/mL ampicillin were added. Cells were grown in 96-well microtiter plates for 24 hours at 30° C. with shaking. 50 μl of the preparatory cultures were transferred to 96-well plates with 400 μl fresh HEPES (100 mM) buffered medium containing 0.3 mM IPTG to induce expression of wbgL genes in pDEST. Induced cultures were grown for two days at 30° C. with shaking. Cells were sedimented by centrifugation and the supernatant was used for detection of free L-fucose.
E. coli BL21(DE3) containing pDEST: wbgL (H124A E215G) and pDEST:futC, respectively, was grown in 2YT broth (Sambrook, J. and Russell D. W. (1989) Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.) at 30° C. to an OD600 nm of 0.3 in the presence of 100 μg/mL ampicillin. Transcription of wbgL (H124A E215G) and futC was induced by addition of 0.3 mM IPTG. Cells were harvested by centrifugation 20 h after induction. Cells were used for analysis of in vitro GDP-L-fucose hydrolase activity.
Enzyme Assays to Detect Free L-Fucose and In Vitro GDP-L-Fucose Hydrolase Activity
Free L-fucose was measured in a colorimetric assay using L-fucose dehydrogenase (FuDH) from Pseudomonas sp. No. 1143 (acc. no. D32042) that catalyzes the NADP-dependent transformation of L-fucose to L-fucono-1,5-lactone. In the colorimetric assay nitroblue tetrazolium in the presence of phenazine methosulfate is reduced to a blue-purple formazan by NADPH. Formation of the formazan is monitored at 571 nm. (Mayer, K. M. and Arnold, F. H. (2002) A Colorimetric Assay to Quantify Dehydrogenase Activity in Crude Cell Lysates. J. Biomol. Screen. 7, 135-140).
The fuDH gene from Pseudomonas sp. No. 1143 was overexpressed in E. coli BL21(DE3). The recombinant FuDH protein that contained an N-terminal His6-tag was enriched from crude extract by immobilized-metal affinity chromatography using a Ni Sepharose™ 6 Fast Flow column (GE Healthcare, Pollards Wood, UK).
To detect free L-fucose in cultures of the fucose E. coli BL21(DE3) production strain harboring pDEST:wbgL(error-prone) each 200 μl L-fucose dehydrogenase assay reaction contained 50 μl cell culture supernatant and 150 μl of reagent solution that consists of 0.8 mM NADPH, 0.3 mM nitroblue tetrazolium, 0.03 mM phenazine methosulfate and 4.7 Units His6-FuDH in 50 mM Tris (pH 8.0) with 0.13% (w/v) gelatin (all chemicals were purchased from Sigma Aldrich, St. Louis, USA). Formation of the blue-purple formazan was measured after 10 min incubation at room temperature at 571 nm.
To detect GDP-L-fucose hydrolase activity in cell lysates of E. coli BL21(DE3) pDEST:wbgL (H124A E215G) and E. coli BL21(DE3) pDEST:futC cells were resuspended in 50 mM HEPES buffer (pH 7.5) with 5 mM MnCl₂and disrupted using glasbeats and a Mini-Beatbeater (BioSpec Producs, Bartlesville, USA). L-fucose was cleaved from GDP-L-fucose in a GDP-L-fucose hydrolase assay. 200 μl of the hydrolase assay contained 12.5 μl of 100 mM GDP-L-fucose (Sigma Aldrich, St. Louis, USA) in 50 mM HEPES buffer (pH 7.5), 5 mM MnCl₂and 50 μl cell free extract.
To verify stability of GDP-L-fucose the hydrolase assay was also performed with 50 μl bovine serum albumin (30 mg/mL) instead of crude extract. Protein concentrations were estimated according to Bradford using a commercially available dye solution (Roti-Quant®, Carl Roth, Karlsruhe, Germany). After one hour incubation at 30° C. the enzymes in the GDP-L-fucose assays were inactivated by heating to 95° C. for 10 min. 50 μl of the GDP-L-fucose hydrolase assay reaction mixture were used to detect free L-fucose using the L-fucose dehydrogenase assay. This assay was set up as described above and incubated for 24 h at room temperature.
LC-MS/MS Analysis
Mass spectrometry analysis was performed by MRM (multiple reaction monitoring) using a LC Triple-Quadrupole MS detection system (Shimadzu LC-MS 8050) (Shimadzu Corporation, Kyoto, Japan). Precursor ions are selected and analyzed in quadrupole 1, fragmentation takes place in the collision cell using argon as CID gas, selection of fragment ions is performed in quadrupole 3.
Chromatographic separation of fucose and maltotriose after dilution of culture supernatant and reaction mixture from in vitro assay, respectively, 1:100 with 10 μg/mL maltotriose in H₂O (LC/MS Grade), was performed on a XBridge Amide HPLC column (3.5 μm, 2.1×50 mm (Waters, USA) with a XBridge Amide guard cartridge (3.5 μm, 2.1×10 mm) (Waters, USA). The HPLC system consists of a Shimadzu Nexera X2 SIL-30AC_MPAutosampler run at 8° C., a Shimadzu LC-20AD Pump, and a Shimadzu CTO-20AC column oven that was run at 30° C. (Shimadzu Corporation, Kyoto, Japan). The mobile phase was composed of acetonitrile:H₂O (62:38% (v/v)) with 10 mM ammonium acetate. A 1 μl sample was injected into the instrument; the run was performed for 3 min with a flow rate of 300 μl/min. L-fucose and maltotriose (added as internal standard for normalization) were analyzed by MRM in ESI negative ionization mode. The mass spectrometer was operated at unit resolution. Fucose forms an ion of m/z 163.2 [M-H] and maltotriose an ion of m/z 503.2 [M-H]. The precursor ion of L-fucose was further fragmented in the collision cell into the fragment ions m/z 88.9, m/z 70.8 and m/z 58.9. The molecular ion of maltotriose (m/z 503.2) was fragmented into m/z 341.1, m/z 161.05 and m/z 100.9. Collision energy, Q1 and Q3 Pre Bias were optimized for each analyte individually.
Results
Synthesis of Free L-Fucose by the E. coli BL21(DE3) Production Strain Expressing a Fucosyltransferase Gene
To enhance GDP-L-fucose synthesis in E. coli BL21(DE3) heterologous genes encoding phosphomannomutase, mannose-1-phosphate guanosyltransferase, GDP-mannose-4,6-dehydratase, and GDP-L-fucose synthase were genomically integrated and overexpressed. Additionally, to confer to the BL21(DE3) strain the ability to grow on sucrose, the csc-gene cluster, encoding sucrose permease, fructokinase, sucrose hydrolase and a transcriptional repressor, from E. coli W was integrated in the genome.
The 2-fucosyltransferase WbgL catalyzes the transfer of L-fucose from the donor molecule GDP-L-fucose to an acceptor oligosaccharide. However, in the absence of an acceptor molecule free L-fucose could be detected in the supernatant of the bacterial cultures, when growing the E. coli BL21(DE3) production strain harboring pDEST:wbgL in an appropriate medium. Free L-fucose is released from GDP-fucose by the GDP-L-fucose hydrolase activity of WbgL.
To further improve the GDP-L-fucose hydrolase activity of WbgL the wbgL gene was subjected to random mutagenesis using error-prone PCR. A library of about 5000 E. coli BL21(DE3) production strains harboring pDEST:wbgL(error-prone) clones was tested for improved GDP-L-fucose hydrolase activity. Two clones (designated as clones D1 and H2) showed increased production of free L-fucose, as determined by analysis of culture supernatants using the L-fucose dehydrogenase assay (FIG. 1). Two amino acid substitutions were found in the WbgL sequence of each of the two clones. The WbgL variant of clone D1 contained amino acid substitutions histidine 124 to alanine and glutamate 215 to glycine, in the WbgL variant of clone H2 residue asparagin 69 was exchanged to serine and isoleucine 268 to proline.
Supernatants of the E. coli BL21(DE3) production strain harboring plasmids pDEST:wbgL, pDEST:wbgL(H124A E215G) D1 and pDEST:wbgL(N69S I268P) H2 were also subjected to LC-MS/MS analysis. L-fucose was identified by MRM analysis in each sample. The amount of free L-fucose was determined using maltotriose as an internal standard for normalization. For the strain expressing the wbgL wild-type gene 0.12 g/L L-fucose were determined in the culture supernatant. Hydrolytic activity of WbgL variants (H124A, E215G), and (N69S, I268P) was clearly increased. Clones D1 and H2 produced 0.43 g/L and 0.25 g/L L-fucose, respectively (FIG. 2).
Detection of GDP-L-Fucose Hydrolase Activity in Cell Lysates of Microorganisms Expressing Fucosyltransferase Genes
GDP-L-fucose hydrolase activity was analyzed in cell free extracts of E. coli BL21(DE3) pDEST:wbgL (H124A E215G) and E. coli BL21(DE3) pDEST:futC, grown in the presence of the transcriptional inducer IPTG. The 2-fucosyltransferase FutC is described to hydrolyze GDP-L-fucose in the absence of an oligosaccharide substrate (Stein, D. B., Lin Y.-N., Lin, C.-H. (2008) Characterization of Helicobacter pylori α1,2-fucosyltransferase for enzymatic synthesis of tumor-associated antigens. Adv. Synth. Catal. 350, 2313-2321). GDP-L-fucose was cleaved in the hydrolase assay that contained 5 mM GDP-L-fucose and cell lysates of the respective strains. Using the L-fucose dehydrogenase assay free L-fucose was detected. No free L-fucose was detected in the assay containing bovine serum albumin instead of crude extract, demonstrating stability of GDP-L-fucose (FIG. 3).
For quantification of the L-fucose released by in vitro hydrolyses of GDPL-fucose the hydrolase assays were cleared by solid phase extraction using ion exchange cartridges (Strata ABW, Phenomenex, Aschaffenburg, Germany) and analyzed by LCMS/MS. In assays containing cell lysates of the futC, and wbgL(H124A E215G) expressing strains, 0.38 g/L and 0.32 g/L L-fucose, respectively, were measured after 1 hour incubation, corresponding to specific GDP-L-fucose hydrolase activities of 0.18 U/mg for FutC and 0.21 U/mg for WbgL (H124A E215G).

Claims

1. Process for producing a monosaccharide of interest in free form using a microorganism, the process comprising

a.) providing a microorganism for the synthesis of the monosaccharide comprising an enzyme capable of catalyzing the hydrolysis of a nucleotide-activated monosaccharide to release the monosaccharide of interest from the nucleotide-activated monosaccharide, and

b.) cultivating the microorganism in a medium suitable for growing the microorganism, wherein the microorganism is unable to metabolize the monosaccharide to a significant extent, so that the monosaccharide of interest accumulates during cultivation.

2. The process of claim 1, wherein a recombinant microorganism is used, wherein the recombinant microorganism comprises a heterologous nucleic acid encoding an enzyme capable of catalyzing the hydrolysis of a nucleotide-activated monosaccharide.

3. The process of claim 1, wherein the enzyme is a glycosyltransferase, optionally a fucosyltransferase, the enzyme being able to catalyze the hydrolysis of the nucleotide-activated monosaccharide GDP-fucose in the absence of an acceptor molecule.

4. The process of claim 1, wherein the enzyme is a variant of the 2-fucosyltransferase encoded by the wbgL gene from Escherichia coli, or a variant of the 1,2-fucosyltransferase encoded by the futC gene from Helicobacter pylori, the variant carrying at least one, optionally at least two, and optionally more than two modifications as compared to the wild type 2-fucosyltransferase encoded by the wbgL gene or to the wild type 1,2-fucosyltransferase encoded by the futC gene, respectively, the modification leading to an increased hydrolizing activity of the enzyme.

5. The process of claim 4, wherein at least one modification is an amino acid substitution.

6. The process of claim 1, wherein the microorganism is further modified to have inactivated or severely reduced or to lack catabolic pathways leading to the degradation of the produced monosaccharide.

7. The process of claim 1, wherein the microorganism is further modified to have inactivated or severely reduced or to lack genes involved in the catabolism of L-fucose.

8. The process of claim 1, wherein the microorganism is further modified to overexpress at least one gene involved in the biosynthesis of the nucleotide-activated monosaccharide to improve supply of the nucleotide-activated monosaccharide of the monosaccharide.

9. The process of claim 1, wherein at least one gene involved in the biosynthesis of GDP-fucose, GDP-mannose or GDP-rhamnose is overexpressed to improve supply of GDP-fucose, GDP-mannose or GDP-rhamnose, respectively.

10. The process of claim 8, wherein the at least one gene is heterologous or homologous.

11. The process of claim 1, wherein the microorganism is further modified to have inactivated or reduced competing pathways for the nucleotide-activated monosaccharide.

12. The process of claim 1, wherein the monosaccharide produced is selected from L-fucose, L-rhamnose, or L-mannose.

13. The process of claim 1, wherein the microorganism is cultivated in a medium containing an inexpensive carbon source that is selected but not limited to glycerol, sucrose, glucose, fructose, molasse, xylose, cellulose, syngas, corn-syrup or lactose.

14. The process of claim 1, wherein the microorganism is further modified to express a phosphatase, in case where the monosaccharide is released in a phosphorylated form by the enzyme.

15. Recombinant microorganism comprising a heterologous enzyme capable of catalyzing the hydrolysis of a nucleotide-activated monosaccharide and releasing the monosaccharide from the nucleotide-activated monosaccharide in the absence of an acceptor molecule, wherein the enzyme is a glycosyltransferase, optionally a fucosyltransferase.

16. The recombinant microorganism of claim 15, wherein the enzyme is a variant of the 2-fucosyltransferase encoded by the wbgL gene, or a variant of the 1,2-fucosyltransferase encoded by the futC gene from Helicobacter pylori, the variant carrying at least one, optionally at least two, and optionally more than two modifications as compared to the wild type 2-fucosyltransferase encoded by the wbgL gene or to the wild type 1,2-fucosyltransferase encoded by the futC gene, respectively, the modification leading to an increased hydrolizing activity of the enzyme.

17. The recombinant microorganism of claim 15, that is further modified to comprise heterologous genes encoding phosphomannomutase, mannose-1-phosphate guanosyltransferase, GDP-mannose-4,6-dehydratase, and GDP-L-fucose synthase.

18. The process of claim 1, wherein or recombinant host microorganism produced therefrom wherein the host microorganism is an Escherichia coli strain, Corynebacterium spp., Clostridium spp., Bacillus spp. Pseudomonas spp. Lactobacillus spp. or a Saccharomyces sp. strain.