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PubMed1989

Glucosyltransferases of Streptococcus sobrinus C211 are both stimulated and inhibited by hydrogen peroxide.

There are 2 glucosyltransferases (GTF) produced by Streptococcus sobrinus C211. One enzyme, GTF-S, produces a water-soluble glucan that is a-1,6-linked, with short a-1,3 branches, and the other enzyme, GTF-I, produces a water-insoluble glucan that is a-1,3-linked with a-1,6 branches. Hydrogen peroxide was found not only to be a potent inhibitor of GTF activity, but also a stimulator of GTF activity when employed at relatively low concentrations. At 0.88 M, H2O2 completely inhibited insoluble glucan synthesis, whereas at a 0.29 M concentration, H2O2 enhanced synthesis of the same glucan. Soluble glucan synthesis was also inhibited by H2O2 at 1.47 M. Low concentrations of hydrogen peroxide with GTF-S, however, caused the enzyme to convert from soluble glucan production to insoluble glucan production. 13C-Nuclear magnetic resonance spectra of glucans produced by peroxide-treated GTF confirmed that the production of a-1,3 linked glucans was increased with H2O2-treated GTF-S.

Glucans↗
PubMed1990

Glucosyltransferase production by Streptococcus sanguis Challis and comparison with other oral streptococci.

Glucosyltransferase (GTF) activity in batch cultures of Streptococcus sanguis strain Challis in defined medium was maximum at peak growth and declined rapidly on further incubation into stationary phase. Activity was present in spent culture medium and was associated with 2 polypeptides of approximate Mrs 170 kDa (90% of activity) and 155 kDa (about 10% of activity). Other S. sanguis strains produced similar antigenically-related polypeptides but with varying activities, and antibodies to the S. sanguis enzyme did not react with enzymes produced by other species of oral streptococci. Increasing the [Na+] reduced GTF production by S. sanguis strains Challis and NCTC 7865, and by Streptococcus sobrinus, but not by Streptococcus salivarius. Addition of Tween 80 to cultures caused a rapid inhibition of GTF synthesis by strain Challis, but not by strain NCTC 7865. Benzyl alcohol had a slower and less inhibitory effect on GTF production by strain Challis. Tween 80 generally inhibited to varying degrees GTF production by other oral streptococci through in S. sobrinus it was stimulated. The results suggest controls operating on GTF synthesis and secretion by different strains of oral streptococci appear to be diverse.

Animals↗
PubMed1990

Interaction of structural isomers of sucrose in the reaction between sucrose and glucosyltransferases from mutans streptococci.

Structural isomers of sucrose, i.e. disaccharides composed of glucose and fructose molecules with different glucosidic linkages, were examined for their effect on the reaction between sucrose and various glucosyltransferases (GTases) from Streptococcus mutans MT8148 and Streptococcus sobrinus 6715. Trehalulose (alpha 1-1), turanose (alpha 1-3), maltulose (alpha 1-4), and palatinose (alpha 1-6) were used as the sucrose analogues. Mutans streptococci were found not to utilize these sucrose analogues. Analysis of enzymatic products of GTase and sucrose with thin layer chromatography clearly revealed that glucan synthesis from [14C]sucrose by the various purified GTase preparations from S. mutans and S. sobrinus was inhibited in the presence of these sucrose analogues except turanose, resulting in the release of increased amounts of [14C]fructose and [14C]oligosaccharides. It was also found that the fructose residues in the oligosaccharides were derived from those of sucrose analogues but not sucrose itself. The Lineweaver-Burk plots of the substrate saturation kinetics of GTase vs sucrose indicated increased Km and Vmax in the presence of sucrose analogue, as compared with sucrose alone. Finally, these sucrose analogues except turanose inhibited sucrose dependent cellular adherence of S. sobrinus 6715 to a glass surface, while they scarcely inhibited the adherence of S. mutans MT8148. Among the analogues, maltulose appeared the most effective inhibitor against GTases in general.

Chromatography, Thin Layer↗
PubMed1992

Glucosyltransferase phase variation in Streptococcus gordonii modifies adhesion to saliva-coated hydroxyapatite surfaces in a sucrose-independent manner.

Phase variation of Streptococcus gordonii between high (Spp+) and low (Spp-) levels of glucosyltransferase (GTF) activity resulted in the greater adhesion of Spp- strains to saliva-coated hydroxyapatite (S-HA) in a washed-cell adhesion test. Specific GTF mutants did not show this response. Although washed Spp+ cells produced 5-fold or more glucan from sucrose than Spp- cells did under the conditions of the adhesion test, sucrose elevated the adhesion of both phenotypes to hydroxyapatite (HA) equally, but had no effect on adhesion to S-HA. This effect was not sucrose-specific, however, because equimolar amounts of other carbohydrates and NaCl elevated adhesion of both Spp types to levels similar to those seen with sucrose. Adhesion did not correlate with relative changes in cell hydrophobicity. These results suggest that, in addition to changes in GTF activity, other changes relevant to adhesion may occur during Spp phase variation.

Arabinose↗
PubMed1994

Oral immunization of humans with dehydrated liposomes containing Streptococcus mutans glucosyltransferase induces salivary immunoglobulin A2 antibody responses.

Seven healthy adult volunteers each ingested an enteric-coated capsule containing 500 micrograms of Streptococcus mutans glucosyltransferase (GTF) in dehydrated liposomes for 3 consecutive days. The immunization regimen was repeated 28 days later. Parotid saliva and plasma were collected prior to and at a weekly interval for 8 weeks following the first immunization for analysis of anti-GTF activity by enzyme-linked immunosorbent assay. The levels of immunoglobulin A1 (IgA1) and IgA2 anti-GTF activities increased in the parotid saliva from 5 of 7 individuals after immunization. Increases in the mean level of IgA1 and IgA2 anti-GTF responses peaked on day 35 (77% and 175% increase over baseline, respectively), although variation was noted in the kinetics and subclass of responses between individuals. No salivary IgG or IgM responses were observed. Low plasma IgM, IgG and IgA anti-GTF responses were seen in immunized subjects. Oral immunization with a dehydrated liposome-protein vaccine was effective in inducing a secretory IgA antibody response, which was primarily of the IgA2 subclass. These results provide the first evidence for the use an oral dehydrated liposome-protein vaccine in humans.

Administration, Oral↗
PubMed1996

Properties of practical oral liposome-Streptococcus mutans glucosyltransferase vaccines for effective induction of caries protection.

Here we report the effectiveness of various liposome vaccines containing Streptococcus mutans glucosyltransferase (GTF) in protecting against dental caries after oral immunization. Rats were immunized by gastric intubation of the appropriate liposome vaccine at weaning and boosted 3 times. Rats were infected with S. mutans following initial immunization and fed cariogenic diet (Diet 305). Saliva and serum were collected during the study and assessed for antibody activity by enzyme-linked immunosorbent assay. Mandibles were removed on day 47 and assessed for S. mutans levels and then for caries. Animals immunized with sonicated, filtered and microemulsified GTF liposome preparations had decreased levels of dental caries compared with control animals given empty liposomes. Rats given dehydrated/rehydrated or purified liposomal GTF also had significantly less caries than control group (GTF alone). Because of economy, ease of preparation and efficiency in amount of antigen used, filtered, dehydrated/ rehydrated and purified liposomal GTF preparations are most practical for use in further assessing the efficacy of liposomal GTF in oral immunization.

Analysis of Variance↗
PubMed1975

Glucosylation of galactosylhydroxylysyl residues in collagen in vitro by collagen glucosyltransferase. Inhibition by triple-helical conformation of the substrate.

Glucosylation of galactosylhydroxylysyl residues in various collagen polypeptide chains and in small peptides prepared from collagen was studied in vitro using collagen glucosyltransferase purified about 200 to 500-fold from extract prepared from chick embryos. When various denatured polypeptide or peptide chains were compared as substrates for the enzyme, no significant differences were found between citrate-soluble collagens from normal or lathyritic rats and isolated alpha1 and alpha2 chains. In contrast, gelatinized insoluble calf skin collagen, and peptides prepared from collagen and having an average molecular weight of about 500 were clearly less effective substrates as judged from their Km and V values. A marked difference was found between native and heat-denatured citrate-soluble collagen in that no synthesis of glucosylgalactosylhydroxylysine was observed with the native collagen when the reaction was studied at 30 degrees C with different times, enzyme concentrations, and substrate concentrations. When the reaction was studied as a function of temperature, little glucosylation of native collagen was observed below 37 degrees C, but there was a sharp transition in the rate of glucosylation of native collagen at temperatures above 37 degrees C, similar to that observable in the melting curve of collagen. The data suggest that triple-helical conformation of collagen prevents that glucosylation of galactosylhydroxylysyl residues.

Animals↗
PubMed1976

Studies on the mechanism of collagen glucosyltransferase reaction.

The mechanism of collagen glucosyltransferase reaction was studied with enzyme preparations purified about 2500-5000-fold from extract of homogenate of whole chick embryos. Data obtained in experiments on initial velocity and inhibition kinetics of the reaction were consistent with an ordered mechanism in which the substrates are bound to the enzyme in the following order: Mn2+, UDP-glucose and collagen substrate, the addition of Mn2+ being at thermodynamic equilibrium and the binding site of the UDP-glucose to the enzyme not being the same as that for Mn2+ and collagen substrate. Only one metal co-factor seems to be involved in the reaction. The collagen substrate can probably also react in some conditions with enzyme-Mn2+ and with enzyme-Mn2+-UDP, and the UDP with the free enzyme, but in all these instances dead-end complexes are formed. Evidence is presented for an ordered release of the products in the following order: glucosylated collagen, UDP and Mn2+, in which Mn2+ need not leave the enzyme during each catalytic cycle.

Animals↗
PubMed1982

Enzymic synthesis of lignin precursors. Purification and properties of UDP glucose: coniferyl-alcohol glucosyltransferase from cambial sap of spruce (Picea abies L.).

UDPglucose:coniferyl-alcohol glucosyltransferase was isolated from cambial sap of spruce (Picea abies). An apparently homogeneous enzyme was obtained by a seven-step procedure including dye-ligand chromatography. The enzyme has an Mr of about 50 000 and consists of one polypeptide chain. Transferase activity is not influenced by metal ions. The enzyme shows a pronounced substrate specificity towards UDPglucose and coniferyl alcohol with Km values of respectively 220 microM and 250 microM. The only reaction product is coniferin (coniferyl alcohol 7-O-beta-D-glucopyranoside). No formation of 'isoconiferin' (coniferyl alcohol 1-O-beta-D-glucoside) was detected. The reversibility of the reaction was proved by formation of [3H]UDPglucose from [3H]UDP and coniferin in the presence of the transferase. The products UDP and coniferin inhibit the reaction noncompetitively. Product inhibition patterns are consistent with a mono-iso-ordered bibi mechanism involving two isomeric enzyme forms.

Cinnamates↗
PubMed1984

Kinetic mechanism of a flavonol-ring-B O-glucosyltransferase from Chrysosplenium americanum.

The kinetic mechanism of a flavonol-ring-B O-glucosyltransferase from Chrysosplenium americanum was investigated. Substrate interaction kinetics for the flavonol and UDPG gave converging lines, which were consistent with a sequential bireactant binding mechanism. They also showed substrate inhibition with respect to the flavonol. Intercept and slope replots were linear and gave a KA of 250 microM and a KB of 10 microM. Product-inhibition studies showed competitive inhibition between UDPG and UDP (KiQ 20 microM) and non-competitive inhibition between the flavonol substrate and its glucoside (KiP 1 mM). Kinetic patterns were consistent with an ordered bi-bi mechanism, where UDPG is the first substrate to bind to the enzyme and UDP is the final product released. The high KiP value, as compared with that of KB, indicates that the reaction is not inhibited by the glucosylated products formed and conforms with the accumulation of flavonol glucosides in C. americanum.

Glucosyltransferases↗
PubMed1984

pH-induced co-operative effects in hysteretic enzymes. 2. pH-induced co-operative effects in a cell-wall beta-glucosyltransferase.

A beta-glucosyltransferase, extracted and purified from the cell walls of isolated soybean cells, displays hysteretic behaviour. The enzyme is monomeric and has a negative co-operative between pH 5.5 and 7.5. Below and above these pH values, the enzyme follows, or approaches, classical Michaelis-Menten kinetics. The free enzyme and the enzyme-glucose complex exhibit, upon pH jumps, conformational transitions which may be followed by monitoring the fluorescence of enzyme-bound toluidinylnaphthalene sulfonate. Taken together these results are consistent with the model of pH-induced co-operativity described in the preceding paper in this journal. This special type of co-operativity relies on a change of the pK value of a strategic ionizable group located outside the active site in a region (or a domain) of the protein which undergoes the conformational transition. The result that at 'low' and 'high' pH values, the enzyme follows or approaches Michaelis-Menten kinetics is explained by assuming that the conformational changes do not affect the active site.

Allosteric Regulation↗
PubMed2004

Effects of Magnolol and Honokiol on the activities of streptococcal glucosyltransferases both in solution and adsorbed on an experimental pellicle.

AIMS: To investigate the inhibitory effects of Magnolol and Honokiol on the activity of streptococcal glucosyltransferases (Gtfs). METHODS AND RESULTS: The effect of Magnolol and Honokiol that inhibits the activities of streptococcal GtfB, GtfC, GtfD and GtfS was explored with standard assays. The results showed that both samples can efficiently inhibit the activity of all Gtfs in solution (66.4-96.3%) and adsorbed on the surface of saliva-coated hydroxyapatite (sHA) beads (65.5-92.7%) at concentrations between 1.25 and 5.0 mg ml(-1). Furthermore, Magnolol had a stronger inhibition of four kinds of Gtfs than Honokiol both in solution and adsorbed on the surface of sHA beads at concentrations between 0.04 and 0.63 mg ml(-1) (P < 0.05). CONCLUSIONS: Magnolol had significant effects on the activities of streptococcal Gtfs. SIGNIFICANCE AND IMPACT OF THE STUDY: Magnolol as a natural herb can be developed into a new oral hygiene product to prevent plaque formation.

Adsorption↗
PubMed1996

Peroxidase-catalyzed generation of catechin oligomers that inhibit glucosyltransferase from Streptococcus sobrinus.

Oolong tea extract (OTE) and the purified polymeric polyphenols from OTE have been found to inhibit glucosyltransferase (GTase) of mutans streptococci. In view of the partial fermentation characteristic of oolong tea, we describe here an in vitro model reaction system to produce partially fermented products of D-(+)-catechin or green tea extract (GTE) using horseradish peroxidase. A dimeric catechin molecule was identified as dehydro-dicatechin A by instrumental analyses. The molecular size of some oligomeric catechins was estimated by the elution profile with HPLC. These catechin oligomers markedly inhibited GTase from Streptococcus sobrinus 6715. As the degree of polymerization of catechin or GTE increased, GTase was inhibited more effectively. These results suggest that polymeric polyphenols found in OTE are synthesized by partial fermentation due to oxidases/peroxidases present in tea leaves.

Bacterial Adhesion↗
PubMed1998

Molecular analyses of glucosyltransferase genes among strains of Streptococcus mutans.

Three glucosyltransferase (GTase) genes (gtfB, gtfC and gtfD) were cloned and sequenced from clinically isolated strains of Streptococcus mutans MT8148 (serotype c), MT4239 (c), MT4245 (e), MT4467 (e) and MT4251 (f), respectively. Comparison of the gtf genes revealed that interstrain difference of gtfB and gtfD was limited, while gtfC showed significant interstrain variations. Similar to gtfB and gtfD, gtfC possessed five direct repeats composed of homologous unit in the carboxyl-terminal portion. The repeating unit consisted of 63-65 amino acid residues and is responsible for glucan binding. The gtfC gene from S. mutans MT4245 lacked the fourth unit. Multiple alignment with the gtf sequence of strain GS-5 (c) revealed several changes in these gtf genes due to frameshift mutations. The peptides encoded by the gtfB, gtfC and gtfD genes of GS-5 were 1, 80, and 32 amino acid residues shorter than those of the test strains except strain MT4245.

Bacterial Proteins↗
PubMed2000

Three-dimensional modelling of the catalytic domain of Streptococcus mutans glucosyltransferase GtfB.

Glucosyltransferases (GtfB/C/D) of Streptococcus mutans, a pathogen for human dental caries, synthesize water-insoluble glucan through the hydrolysis of sucrose. Genetic and biochemical approaches have identified several active sites of these enzymes, but no three-dimensional (3D) structural evidence is yet available to elucidate the subdomain arrangement and molecular mechanism of catalysis. Based on a combined sequence and secondary structure alignment against known crystal structures of segments from closely related proteins, we propose here the 3D model of an N-terminal domain essential for the sucrose binding and splitting in GtfB. A Tim-barrel of (alpha/beta)(8) structural characteristics is revealed and the structural correlation for two peptides is described.

Amino Acid Sequence↗
PubMed1983

Adsorption of glucosyltransferase to saliva coated hydroxyapatite. Possible mechanism for sucrose dependent bacterial colonization of teeth.

Glucosyltransferase (GTF) adsorbed to hydroxyapatite and to saliva coated hydroxyapatite in vitro. Several proteins which are known to be present in the "pellicle" which forms on hydroxyapatite when this mineral is exposed to whole saliva were shown to stimulate or inhibit GTF. It is suggested that these proteins may interact with GTF and cause binding of the enzyme to saliva coated hydroxyapatite. A model is suggested where GTF adsorbed to tooth surfaces may induce binding of microorganisms to tooth surfaces.

Adhesiveness↗
PubMed1989

Why is sucrose so cariogenic? The role of glucosyltransferase and polysaccharides.

Some aspects of the cariogenicity of sucrose are discussed, in particular the data indicating that glucosyltransferase (GTF) mediates the well known stickiness of sucrose exposed S. mutans and plaque in vivo. The non-sucrose dependent colonization of teeth, which has been studied extensively, is judged to be of less importance because S. mutans is only pathogenic in combination with sucrose. Strong evidence from several laboratories show that free GTF is present in saliva and that it adsorbs to the pellicle and is able to form glucan in the adsorbed state. Glucan-glucan interaction between 1-3 linked glucans gives a strong sucrose dependent interaction between glucan chains originating from the GTF adsorbed to the pellicle and from GTF on the bacterial surface.

Bacterial Adhesion↗