WO2001066570A1

WO2001066570A1 - Enzyme capable of hydrolyzing plaque, microorganism producing thesame, and a composition comprising the same

Info

Publication number: WO2001066570A1
Application number: PCT/KR2000/000191
Authority: WO
Inventors: Doman Kim; Do-Won Kim; Soo-Jin Heo; Su-Jin Ryu
Original assignee: Doman Kim; Kim Do Won; Heo Soo Jin; Ryu Su Jin
Priority date: 2000-03-09
Filing date: 2000-03-09
Publication date: 2001-09-13
Also published as: AU3331300A

Abstract

The present invention relates to a dental plaque hydrolyzing or inhibiting enzyme, a preparation method thereof, a composition containing the same and microorganism producing the same.

Description

ENZYME CAPABLE OF HYDROLYZING PLAQUE, MICROORGANISM

PRODUCING THE SAME AND A COMPOSITION COMPRISING THE SAME

TECHNICAL FIELD

The present invention relates to an enzyme capable of hydrolyzing

dental plaque, a microorganism producing the same and a composition comprising the same.

BACKGROUND OF THE INVENTION

Plaque formed on the surface of a tooth is composed of compactly

packed bacteria and non-cellular materials. The main poiysaccharide

component of plaque is water-insoluble glucan or mutan, which constitutes

approximately 20 % of the dried mass of plaque and is a main cause of dental

caries. Structural studies of glucans produced by Streptococos mutans

revealed that the insoluble glucans are mainly composed of α-1 ,3-, α-1 ,4-, α-

1 ,6-D-glucoside. Therefore, to eliminate plaque effectively, mutanoiytic.

amylolytic. and dextranolytic activities are required.

Conventionally, methods of reducing the growth of Streptococos mutans

(S. mutans) in mouth have been suggested to prevent the formation of plaque or

dental caries. To achieve this, antiseptics or fluoride which inhibit the growth of

S. mutans have been added in oral compositions such as toothpaste or

mouthwash. Fluoride is one of the most widely used chemicals because it reduces the growth of S. mutans. Although fluorine can inhibit the growth of the caries inducing bacteria, it can cause caries-like lesions (formation of orthodontic white spots on tooth enamel) as well as severe side effects such as strong toxicity and air pollution. Enzymes such as dextranase have been used to prevent dental caries, however, its effect has yet to be proven.

US patent number 5,741 ,773 discloses a toothpaste composition comprising glycomacropeptide having antiplaque and anticaries activities.

These conventional techniques relate to the reduction of the bacteria growth that causes dental caries. This invention can prevent the formation of plaque and hydrolyze pre-formed plaque.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an enzyme which can hydrolyze or inhibit dental plaque.

Another object of the present invention is to provide a microorganism which produces a dental plaque hydrolyzing or inhibiting enzyme.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

It has been reported that Lipomyces starkeyi (L. starkeyi) produces endo-dextranase (EC 3 2 1 1 1 ) which degrades dextran and α-amylase which

degrades starch This microorganism has been used in food related applications and is not known to produce antibiotics or toxic metabolites

Except for a few bacterial dextranases, dextranases which are produced

by microorganisms are known to be mducible enzymes The present inventors

have reported that L starkeyi ATCC 74054 produces both dextranase and

amylase (US patent 5,229,277) while disclosing the characteristics of the

enzyme produced by the same microorganism The present inventors have

also reported that these microorganisms can produce small molecular weight

dextrans by using sucrose and/or starch

The present invention relates to an enzyme that can inhibit the formation

of or degrade dental plaque

The enzyme of the present invention degrades dextran and starch as

well as insoluble glucans and will be referred to as DXAMase hereinafter

DXAMase according to the present invention mainly produces glucose,

isomaltose and branched tetrose and small amounts of branched pentose and

hexose when dextran is used as a substrate When starch is used as a

substrate, DXAMase can mainly produce glucose, maltose, maltotπose and

maltotetraose as well as a variety of malto-oligosacchaπdes

Since DXAMase can degrade levan which is a polymer of β-fructan,

DXAMase according to the present invention can effectively degrade fructan

forming plaque

DXAMase according to the present invention, therefore, can effectively

degrade soluble as well as insoluble glucans and fructan DXAMase can effectively prevent dental caries since plaque formation can be inhibited by preventing the aggregation of glucan and microorganisms or pre-formed plaque can be eliminated.

Experimental results using hydroxyapatite, which is similar in composition with dental materials, indicate that DXAMase has a stronger binding with hydroxyapatite than P. funiculosum dextranase. Therefore, it is expected that DXAMase will have a higher chance to retain on the tooth surface.

DXAMase according to the present invention is stable in a variety of mouthwash. Moreover, DXAMase does not lose its enzymatic activity in the presence of by chlorhexidine which is currently used as a remedy of periodontal disease.

DXAMase can be isolated from L starkeyi ATCC 74054 or L. starkeyi

KSM 22. In other words, DXAMase is isolated from a culture medium of L. starkeyi ATCC 74054 or L starkeyi KSM 22, and is identified by double bands of 94K and 60K on a SDS-PAGE (10%) eletrophoresis whose pi is 6.0 for both bands.

The present invention also relates to a new microorganism that produces DXAMase. L. starkeyi KSM 22 was obtained by mutating L. starkeyi ATCC 74054 and has a higher productivity of DXAMase than L. starkeyi ATCC 74054. The present microorganism, L. starkeyi KSM 22 has been deposited with Korean Federation of Culture Collections (KFCC) located at Shinchon-dong 134, Seodaemun-ku, Seoul, Korea on Jan. 19, 1999 and was given number KFCC- 11077. The same line was also deposited according to the Budapest Treaty at the depository Korean Culture Center of Microorganisms (KCCM) and was given deposit number KCCM-10181 on Mar. 7, 2000.

The present invention also relates to a method of producing DXAMase. The method of the present invention comprises culturing L. starkeyi ATCC 74054 or L. starkeyi KSM 22 and recovering DXAMase from the culture medium. Since L starkeyi ATCC 74054 and L starkeyi KSM 22 can produce DXAMase

from not only the expensive dextran but also relatively cheap glucose, fructose,

sucrose or starch, it is economical for practical use. DXAMases obtained from

L. starkeyi ATCC 74054 and isolated from L. starkeyi KSM 22 are practically

identical.

Also the present invention relates to an anticaries composition

comprising DXAMase. The composition according to the present invention can

be used as an additive of a composition for oral hygiene such as toothpaste and

mouthwash and food such as candy, chewing gum and beverage. The enzyme

according to the present invention maintains its enzymatic activity for a long

period of time in commercially available mouthwash solutions and has a strong

resistance against enzyme inhibitors. It will be understood that the components

of the oral composition and of food ingredients can be verified without difficulties

within known conventional limits as will be apparent to those skilled in this art.

Definitions

Dextranase activity is determined by measuring the amount of

isomaltose produced by the reaction of an enzyme solution in a buffer solution

containing 2% dextran for 15 min at 37 °C. Dextranase 1 IU is defined as the amount of the enzyme that produces 1 μmol of isomaltose when reaction is

carried out by using dextran as a substrate for 1 min at 37 °C.

Amylase activity is measured by reacting the enzyme solution in a buffer

solution containing 2 % starch for 15 min at 37 °C.

Minimum salt medium: (NH₄)₂S0₄ 0.5%(w/v); KH₂P0₄ 0.15%(w/v); MgS0₄.7H₂0 0.01%(w/v); NaCI 0.01 %(w/v); CaCI₂2H₂0 0.01 %(w/v)

LW medium: yeast extract 0.3%(w/v); KH₂P0₄ 0.3%(w/v)

Glucan hydrolysis rate =

^f reducing sugar produced^ ^f reducing sugar produced ^

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a graphical representation of the effect of pH on relative amylase activity of DXAMase.

FIG. 1b is a graphical representation of the effect of pH on relative

dextranase activity of DXAMase. FIG. 2a is a graphical representation of the effect of temperature on relative amylase activity of DXAMase.

FIG. 2b is a graphical representation of the effect of temperature on

relative dextranase activity of DXAMase.

Figure 3 is a TLC result showing that DXAMase has an ability to degrade

levan.

Figure 4 is a graphical representation of the prevention of cell aggregation by DXAMase.

Figure 5 is a graphical representation of the prevention of plaque

formation as a function of DXAMase concentration.

Figure 6 is a bar graph representing that DXAMase can remove the pre¬

formed plaque.

Figure 7 is a bar graph representing that DXAMase in mouthwash can

prevent glucan formation. Figure 8 is a bar graph representing that DXAMase in mouthwash can

remove the pre-formed insoluble glucan.

Figure 9 is a bar graph representing the stability of DXAMase in a

commercially available mouthwash solution.

Having described the method of this invention, the following figures and

examples will serve to further illustrate the method and describe the best mode

known to the inventors for carrying out the method, but not limited to the

examples given. EXAMPLE 1.

After cultu ng L. starkeyi ATCC 74054 in 1 % solution of minimum salt medium supplemented with 0.5 % dextran and 0.1 % yeast extract for 4 days at

28 °C, the cells were suspended in sterilized 100 mmol^"1 phosphate buffered

saline solution (pH 7.0). After treating 1 ml of cell suspension with 100 μl of

ethylmethanesulfonate (EMS) for 5min, 10 min, and 20 min, sodium thiosulfate (10 %, w.v) was added. The upper layer of the two layer agar plate consists of minimum salt medium containingl % starch, 0.05 % 2-deoxy-D-glucose and 1.5 % agar, and the lower layer consists of blue dextran (0.4% w/v) and 1.5 % agar. By observing the degree of formation of transparent circle of blue dextran and performing iodine experiment, a strain that had excellent dextranase as well as amylase activities was selected and named L starkeyi KSM 22.

EXAMPLE 2.

L starkeyi KSM 22 was cultured in a 4 L fermentor vessel with LW

medium (pH 4.0) containing 1 % starch at 30 °C and 100 rpm. After precipitation

of 3 L culture supernatant to 300 ml by adding 70 % ammonium sulfate, the solution was further concentrated to 50 mL by filtering through a 30 K molecular weight cut-off membrane. The concentrated solution was loaded onto a CM- sepharose column equilibrated with 20 mM potassium phosphate buffer solution (pH 6.0) and eluted with 20 mM potassium phosphate buffer solution (pH 6.0) containing 0.5 M NaCI. The fraction that showed dextranase and amylase activities simultaneously was collected and concentrated by adding isopropanol. Three milliliters of the concentrated solution was loaded onto BIO-RAD A-0.5 column equilibrated with 50 mM citrate phosphate buffer solution (pH 5.5) to perform gel permeation chromatography. The fractions that showed dextranase activity were collected. Two bands at 94 K and 60 K that showed dextranase and amylase activities simultaneously were obtained by performing SDS-PAGE (10 %).

Example 3.

The following 50 mM buffer solutions of pH 2.5-7.5 were used to determine the optimum pH of dextranase and amylase activities of the enzyme obtained in Example 2.

Citrate/phosphate buffer solution (pH 2.5~3.5),

Pyridine acetate buffer solution (pH 4.0~5.5), Phosphate buffer solution (pH 6.0-7.5).

The results are shown in Figures 1a and 1b. The stability of dextranase activity and amylase activity as a function of pH was measured after reacting the

enzyme stock for 72 hours at 22 °C at each pH. Dextranase activity was stable

in the pH range of 2.0-7.5 and amylase activity was stable in the pH range of

4.0-6.0.

To determine the optimum temperature range, dextranase activity and amylase activity were measured after reacting for 15 min in a pH 5.5 buffer solution at different temperatures. The results are shown in Figures 2a and 2b. To estimate the temperature stability, the enzyme stock (5 IU) was diluted with a pH 5.5 buffer solution and reacted for 3 min at each temperature before measuring the enzyme activity. At least 80 % of the initial dextranase and

activity were maintained below 50 °C and 80 °C, respectively.

Example 4. Hydrolysis of glucan

Glucosyltransferase isolated from S. mutans was used to prepare the

following insoluble glucan. After culturing S. mutans at 37 °C for 1 day in LW

medium (pH 7.0), the supernatant was separated. One liter of the obtained supernatant was mixed with 1 L of 200 mM sucrose solution prepared with 20 mM phosphate buffer solution (pH 7.0) and incubated for 24 hours before centrifuging to collect the insoluble glucan. The insoluble glucan was suspended in citrate-phosphate buffer solution (20 mM, pH 5.5) at the concentration of 5 mg/mL to prepare an insoluble glucan suspension solution.

Also soluble glucan T-2000 (Pharmacia Co. Sweden) was dissolved in citrate- phosphate buffer solution (20 mM, pH 5.5) at 5 mg/mL to prepare soluble glucan solution. In 1 mL of each glucan sample, 5 IU of enzyme obtained in

Example 2 was added and reacted for 48 hours at 37 °C. The reaction product

was identified by TLC. The result is summarized in Table 1.

L. starkeyi ATCC 74054 was cultured in 4 L of LW medium containing

1 % starch and 0.05 % deoxy-D-glucose at pH 4.0, 30 °C at an aeration of 1.0 ppm for 72 hours. The enzyme was isolated by using an identical method as in Example 2. The above experiment was repeated by using L. starkeyi ATCC 74054. The result is shown in Table 1. The DXAMases produced from Lipomyces starkeyi ATCC 74054 and Lipomyces starkeyi KSM 22 were almost identical.

Also, dextranase (Sigma) produced by Penicillium funiculosum was used to repeat the above experiment. The result is also shown in Table 1.

TABLE 1.

Example 5. Hydrolysis of Levan

Levan, a β-fructan polymer, was dissolved in a citrate-phosphate buffer

solution (20 mM, pH 5.5). DXAMase 11U was added in 100 μL of levan solution

π and incubated for 1 hour before identifying the products by TLC. The result is shown in Figure 3. Since DXAMase according to the present invention can hydrolyze levan, it is expected that DXAMase can effectively degrade fructan that forms plaque.

Example 6. Inhibition of cell aggregation by glucan

The following experiment was performed to observe the cell aggregation by glucan. In 100 mL of tryptic soy broth containing 0.25 % glucose, S. mutans

was inoculated and cultivated overnight at 37 °C. Cells were harvessted by

centrifugation and washed twice with 5 mM Tris buffer (pH 8.4). The washed cells were suspended in an equal volume of identical buffer solution as the

medium. The mixture of 550 μL of cell suspension and 50 μL of water-soluble

glucan T2000 (dissolved to a concentration of 15 g/mL in 5 mM Tris buffer (pH

8.4)) was treated with 50 μL of DXAMase (0.5 lU/ml). After incubating at 40 °C

for 5 min, the absorbance of the mixture was measured at 5-minute intervals for 60 minutes at A₇₀₀. The absorbance decreased as aggregation between cell and soluble glucan T2000 progressed. When compared to the control without

DXAMase, the degree of aggregation was prohibited by treating with 50 μL of

DXAMase (0.5 lU/ml). The result is shown in Figure 4.

Example 7. Plaque inhibiting and eliminating effect

This experiment was performed by following the method of Schachtele C.F., (Infect. Immun. 1975, 12; 309-317) as follows.

S. mutans suspension solution was prepared by following the method as in Example 5 except that the cultured and collected cells were suspended at 5 %(wet w/v) in a sterile deionized water. To a glass tube, 0.2 mL of cell suspension, 1.0 mL of sucrose solution (concentration of 50 mg/ml dissolved in 100 mM phosphate buffer solution (pH 5.8)), 4.4 mL of sterile deionized water and 0.4 mL DXAMase (equilibrated with 50 mM phosphate buffer solution (pH

5.8)) were added and reacted at 37 °C for 16 - 18 hours without stirring. The

amount of DXAMase was 0 - 2 lU/mL. After carefully removing reaction solution and cells that were not attached, the attached cells were washed with 20 mM phosphate buffer solution (pH 5.8) and suspended by adding 6.0 mL of the identical buffer solution. The turbidity was measured at A₅₅₀. The result is shown in Figure 5. When compared to the control without DXAMase, 80% of insoluble glucan formation was prohibited by treating with 0.1 lU/mL of DXAMase (Figure 5).

To observe whether DXAMase can eliminate pre-formed glucan layer, attachable material consisting of glucan layers was obtained by using the same method as above except the fact that DXAMase was not added. On these attachable cells, 0.5 lU/mL of DXAMase was added and incubated for 24 hours

at 37 °C. After carefully removing reaction solution and cells that were not

attached, the absorbance was measured at A₅₅₀ to determine the amount of attachable material. When compared to the control without DXAMase, approximately 80 % of the attachable film was degraded (Figure 6). Example 8. Binding effect on tooth surface

To confirm the binding effect of DXAMase on the tooth surface, the following expeπment was performed. Hydroxyapatite (Bio-Gel HTP, Bio-Rad Laboratories) was suspended in 10 mM phosphate buffer solution (pH 6.8) and packed in a 1.2 x 5 cm column. In each column, 2 mL(10 lU/ml) of P. funiculosum dextranase (Sigma) dissolved in 10 mM KH₂P0₄(pH 6.8) was loaded. Solutions were eluted by using 10mM - 0.5M phosphate buffer solutions (pH 6.8 for all) to collect 1 ml fractions. In each fraction, both dextranase activity and amylase activity were measured. Identical experiment was also carried out by using DXAMase.

P. funiculosum dextranase exhibited at least 2 peaks, and these two dextranases did not bind on hydroxyapatite and were eluted by 25 mM phosphate buffer solution. In contrast, dextranase activity in the case of DXAMase was eluted by 50, 125, 225 mM phosphate buffer solution, and amylase activity in the case of DXAMase was eluted by 125, 225, 355 mM phosphate buffer solution. From this result, DXAMase is expected to have a higher binding effect on the tooth surface than P. funiculosum dextranase.

Instead of hydroxyapatite, saliva-coated hydroxyapatite was used to carry out the experiment by loading DXAMase of the present invention. Saliva- coated hydroxyapatite was prepared as follows. After collecting saliva from male and female in their 20's and centrifuging to prepare clear solution, the

solution was further filtrated (Whatman, 0.2 μm). One milliliter of the prepared

saliva was mixed with 1 g of hydroxyapatite and incubated for 1 hour. After removing the supernatant by centrifugation and washing with phosphate buffer solution, saliva-coated hydroxyapatite was prepared. DXAMase activity was eluted by using 200-300 mM phosphate buffer solution.

Example 9. Plaque inhibiting and eliminating effect (Co-use with mouthwash solution)

Into a commercially available mouthwash solution product A(Johnson & Johnson), 5 lU/mL of DXAMase obtained from Example 2 was added. Into a glass tube, 0.2 mL of S. mutans suspension obtained by using the method as in Example 4, 1.0 mL of sucrose solution (dissolved at 50 mg/ml in 100 mM phosphate buffer solution (pH 5.8)), 4.4 mL of sterile deionized water and 0.4 mL DXAMase (50 mM phosphate buffer solution (pH 5.8)) were added and reacted

at 37 °C for 16 - 18 hours without stirring. After carefully removing reaction

solution and cells that are not attached, the attached cells were washed with 20 mM phosphate buffer solution (pH 5.8) and suspended by adding 6.0 mL of the identical buffer solution. The turbidity was measured at A₅₅₀. When compared to the control having mouthwash solution without DXAMase, the formation of insoluble glucan with mouthwash solution containing DXAMase was prohibited by 80 %. The result is shown in Figure 7. (1 : sucrose + S. mutans suspension 0.2 mL, 2: sucrose + S. mutans suspension + mouthwash, 3: sucrose + S. mutans + DXAMase, mouthwash).

To evaluate the removable effect of pre-formed glucan layers, attachable cells wherein glucan layer is formed was obtained by using the same method as above except that DXAMase was not added. On these attachable cells, 1 mL of mouthwash solution containing 5 lU/mL of DXAMase was added and incubated for 24 hours at 37 °C. After carefully removing reaction solution and

cells that were not attached, the absorbance was measured at A₅₅₀ to determine the amount of the attachable material. When compared to the control with mouthwash solution product A without DXAMase, approximately 80 % of the attachable film was degraded. The result is shown in Figure 8.

Example 10. Stability test

To test the stabilization of dextranase and amylase activities of DXAMase by chemicals comprising mouthwash solution, the enzyme activity was measured in the presence of the enzyme inhibitors and chemicals in the mouthwash solutions in Table 2. In 1 mL of each chemical solution, 5 IU of

DXAMase was added and reacted for 5 min at 37 °C. Reaction was further

carried out by adding 2 % dextran or starch of an equal volume. Enzyme activity was measured by using a cupper-bicinchoninate reduction number method (Jeffrey D. Fox et al., Analytical Biochemistry 195, 93-96 (1991)). The result is summarized in Table 2. The enzymatic activity did not decrease by various components comprising the mouthwash or by chlorhexidine, which is mainly used to treat periodontal disease. O 01/66570

Table 2

Example 11.

In 4 different commercially available mouthwash solutions, 10 mg/ml of DXAMase, prepared as in Example 2, was added to observe the stability of the enzyme for a 6 month period. The result is shown in Figure 9. (A: Johnson & Johnson, USA, B: Hanmi Pharmaceutical Co., Korea, C: DongA Pharmaceutical Co., Korea, D: ll-Dong Pharmaceutical Co., Korea). After 6 months, at least

93 % of initial dextranase and amylase activities were maintained. (■:

dextranase activity, O amylase activity). Also, in an A oral composition and a B oral composition, more than 90 % of initial activity was maintained after 10 months, and more than 73 % of initial activity was maintained after 22 months.

According to the present invention, a new enzyme that has amylase activity and dextranase activities is provided. Also, the present invention provides an oral composition with an excellent antiplaque and anticaries activities.

Claims

1 . An enzyme having antiplaque and anticaries activities, having a molecular

weight of 94 K measured by SDS-PAGE, having dextranase and amylase

activities simultaneously and degrading insoluble glucans.

2. An enzyme having antipiaque and anticaries activities, having a molecular

weight of 60 K estimated by SDS-PAGE, having dextranase and amylase

activities simultaneously and degrading insoluble glucans.

3. The enzyme according to Claim 1 wherein the above enzyme is isolated

from L. starkeyi KSM 22 or L starkeyi ATCC 74054.

4. L. starkeyi KSM 22 (Deposit No. KFCC-1 1077 or KCCM-10181) producing

the enzyme in Claim 1.

5. A preparation method of DXAMase compπsing of culturing L. starkeyi ATCC

74054 or L. starkeyi KSM 22 and recovering DXAMase from the culture

medium.

6. An oral composition comprising one or more enzymes selected from the

group consisting of an enzyme having antiplaque and anticaries activities,

having a molecular weight of 94 K estimated by SDS-PAGE, having

dextranase and amylase activities simultaneously and degrading insoluble

glucans, and an enzyme having antiplaque and anticaries activities, having

a molecular weight of 60 K estimated by SDS-PAGE, having dextranase and

amylase activities simultaneously and degrading insoluble glucans.