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1.  Structure of the α-1,6/α-1,4-specific glucansucrase GTFA from Lactobacillus reuteri 121 
A 118 kDa fragment, comprising the catalytic domain and four other domains, of the glucansucrase GTFA from L. reuteri 121, which synthesizes α-glucans with both α-1,6- and α-1,4-glycosidic linkages, was crystallized. The weakly diffracting crystals, which contained 85% solvent, were used to determine the structure at 3.6 Å resolution.
The reuteransucrase GTFA from Lactobacillus reuteri 121, which belongs to glycosyl hydrolase family GH70, synthesizes branched α-glucans with both α-­1,6- and α-1,4-glycosidic linkages (reuteran) from sucrose. The crystal structure of GTFA-ΔN, a 118 kDa fragment of GTFA comprising residues 745–1763 and including the catalytic domain, was determined at 3.6 Å resolution by molecular replacement. The crystals have large solvent channels and an unusually high solvent content of 85%. GTFA-ΔN has the same domain arrangement and domain topologies as observed in previously determined GH70 glucansucrase structures. The architecture of the GTFA-ΔN active site and binding pocket confirms that glucansucrases have a conserved substrate specificity for sucrose. However, this first crystal structure of an α-1,6/α-1,4-specific glucansucrase shows that residues from conserved sequence motif IV (1128–1136 in GTFA-ΔN) contribute to the acceptor-binding subsites and that they display differences compared with other structurally characterized glucansucrases. In particular, the structure clarifies the importance of residues following the transition-state stabilizer for product specificity, and especially residue Asn1134, which is in a position to interact with sugar units in acceptor subsite +2.
PMCID: PMC3509963  PMID: 23192022
lactic acid bacteria; glucansucrase; reuteransucrase
2.  Crystallization and preliminary X-ray analysis of Streptococcus mutans dextran glucosidase 
Dextran glucosidase from S. mutans was crystallized using the hanging-drop vapour-diffusion method. The crystals diffracted to 2.2 Å resolution.
Dextran glucosidase from Streptococcus mutans is an exo-hydrolase that acts on the nonreducing terminal α-1,6-glucosidic linkage of oligosaccharides and dextran with a high degree of transglucosylation. Based on amino-acid sequence similarity, this enzyme is classified into glycoside hydrolase family 13. Recombinant dextran glucosidase was purified and crystallized by the hanging-drop vapour-diffusion technique using polyethylene glycol 6000 as a precipitant. The crystals belong to the orthorhombic space group P212121, with unit-cell parameters a = 72.72, b = 86.47, c = 104.30 Å. A native data set was collected to 2.2 Å resolution from a single crystal.
PMCID: PMC2376310  PMID: 17768352
dextran glucosidase; Streptococcus mutans; α-amylase family
3.  Protein preparation, crystallization and preliminary X-ray crystallographic analysis of SMU.961 protein from the caries pathogen Streptococcus mutans  
The SMU.961 protein from S. mutans was crystallized and preliminary characterization of the crystals, which diffracted to 2.9 Å resolution, shows them to belong to space group C2.
The smu.961 gene encodes a putative protein of 183 residues in Streptococcus mutans, a major pathogen in human dental caries. The gene was cloned into expression vector pET28a and expressed in a substantial quantity in Escherichia coli strain BL21 (DE3) with a His tag at its N-terminus. The recombinant protein SMU.961 was purified to homogeneity in a two-step procedure consisting of Ni2+-chelating and size-exclusion chromatography. Crystals suitable for X-ray diffraction were obtained by the hanging-drop vapour-diffusion method and diffracted to 2.9 Å resolution at beamline I911-3, MAX-II-lab, Sweden. The crystal belonged to space group C2, with unit-cell parameters a = 98.62, b = 73.73, c = 184.73 Å, β = 98.82°.
PMCID: PMC2339730  PMID: 17909295
SMU.961; Streptococcus mutans
4.  Preliminary X-ray crystallographic analysis of SMU.2055 protein from the caries pathogen Streptococcus mutans  
The SMU.2055 gene from the major caries pathogen Streptococcus mutans was cloned and native and SeMet-labelled SMU.2055 proteins were expressed at a high level. Diffraction-quality crystals of SeMet-labelled SMU.2055 were obtained using the sitting-drop vapour-diffusion method and diffracted to a resolution of 2.5 Å.
The SMU.2055 gene from the major caries pathogen Streptococcus mutans is annotated as a putative acetyltransferase with 163 amino-acid residues. In order to identify its function via structural studies, the SMU.2055 gene was cloned into the expression vector pET28a. Native and SeMet-labelled SMU.2055 proteins with a His6 tag at the N-terminus were expressed at a high level in Escherichia coli strain BL21 (DE3) and purified to homogeneity by Ni2+-chelating affinity chromatography. Diffraction-quality crystals of SeMet-labelled SMU.2055 were obtained using the sitting-drop vapour-diffusion method and diffracted to a resolution of 2.5 Å on beamline BL17A at the Photon Factory, Tsukuba, Japan. The crystals belong to the orthorhombic space group C2221, with unit-cell parameters a = 92.0, b = 95.0, c = 192.2 Å. The asymmetric unit contained four molecules, with a solvent content of 57.1%.
PMCID: PMC2864685  PMID: 20445252
SMU.2055; Streptococcus mutans; acetyltransferases
5.  Hydroxy decenoic acid down regulates gtfB and gtfC expression and prevents Streptococcus mutans adherence to the cell surfaces 
10-Hydroxy-2-decenoic acid, an unsaturated fatty acid is the most active and unique component to the royal jelly that has antimicrobial properties. Streptococcus mutans is associated with pathogenesis of oral cavity, gingivoperiodontal diseases and bacteremia following dental manipulations. In the oral cavity, S. mutans colonize the soft tissues including tongue, palate, and buccal mucosa. When considering the role of supragingival dental plaque in caries, the proportion of acid producing bacteria (particularly S. mutans), has direct relevance to the pathogenicity of the plaque. The genes that encode glucosyltransferases (gtfs) especially gtfB and gtfC are important in S. mutans colonization and pathogenesis. This study investigated the hydroxy-decenoic acid (HDA) effects on gtfB and gtfC expression and S. mutans adherence to cells surfaces.
Streptococcus mutans was treated by different concentrations of HPLC purified HDA supplied by Iran Beekeeping and Veterinary Association. Real time RT-PCR and western blot assays were conducted to evaluate gtfB and gtfC genes transcription and translation before and after HDA treatment. The bacterial attachment to the cell surfaces was evaluated microscopically.
500 μg ml-1 of HDA inhibited gtfB and gtfC mRNA transcription and its expression. The same concentration of HDA decreased 60% the adherence of S. mutans to the surface of P19 cells.
Hydroxy-decenoic acid prevents gtfB and gtfC expression efficiently in the bactericide sub-concentrations and it could effectively reduce S. mutans adherence to the cell surfaces. In the future, therapeutic approaches to affecting S. mutans could be selective and it’s not necessary to put down the oral flora completely.
PMCID: PMC3495742  PMID: 22839724
Biofilm; Caries; Glucosyltransferase; Streptococcus
6.  Conserved Repeat Motifs and Glucan Binding by Glucansucrases of Oral Streptococci and Leuconostoc mesenteroides 
Journal of Bacteriology  2004;186(24):8301-8308.
Glucansucrases of oral streptococci and Leuconostoc mesenteroides have a common pattern of structural organization and characteristically contain a domain with a series of tandem amino acid repeats in which certain residues are highly conserved, particularly aromatic amino acids and glycine. In some glucosyltransferases (GTFs) the repeat region has been identified as a glucan binding domain (GBD). Such GBDs are also found in several glucan binding proteins (GBP) of oral streptococci that do not have glucansucrase activity. Alignment of the amino acid sequences of 20 glucansucrases and GBP showed the widespread conservation of the 33-residue A repeat first identified in GtfI of Streptococcus downei. Site-directed mutagenesis of individual highly conserved residues in recombinant GBD of GtfI demonstrated the importance of the first tryptophan and the tyrosine-phenylalanine pair in the binding of dextran, as well as the essential contribution of a basic residue (arginine or lysine). A microplate binding assay was developed to measure the binding affinity of recombinant GBDs. GBD of GtfI was shown to be capable of binding glucans with predominantly α-1,3 or α-1,6 links, as well as alternating α-1,3 and α-1,6 links (alternan). Western blot experiments using biotinylated dextran or alternan as probes demonstrated a difference between the binding of streptococcal GTF and GBP and that of Leuconostoc glucansucrases. Experimental data and bioinformatics analysis showed that the A repeat motif is distinct from the 20-residue CW motif, which also has conserved aromatic amino acids and glycine and which occurs in the choline-binding proteins of Streptococcus pneumoniae and other organisms.
PMCID: PMC532428  PMID: 15576779
7.  Antigenic characterization of fimbria preparations from Streptococcus mutans isolates from caries-free and caries-susceptible subjects. 
The adhesion of pathogenic bacteria to the host surface is an essential step in the development of numerous infections, including dental caries. Attachment of Streptococcus mutans, the main etiological agent of human dental caries, to the tooth surface may be mediated by glucan synthesized by glucosyltransferase (GTF) and by cell surface proteins, such as P1, which bind to salivary receptors. Fimbriae on the surfaces of many microorganisms are known to function in bacterial adhesion. Previous studies in this laboratory have initially characterized the fibrillar surface of S. mutans. The purpose of this investigation was the comparison of the antigenic properties of fimbria preparations of S. mutans isolates from five caries-resistant (CR) and six caries-susceptible (CS) subjects. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of S. mutans fimbrial preparations revealed five major protein bands at 200, 175, 157, 86, and 66 kDa in preparations from CR and CS subjects. Immunoblot analysis indicated the presence of the same major bands recognized by anti-S. mutans fimbria antisera. Furthermore, the 175- and 157-kDa bands were recognized by antibodies to P1 and GTF, respectively. Immunoblot analysis with antisera to the fimbria preparation, to P1, or to GTF indicated that the levels of fimbria-reactive components and P1 and GTF antigens were higher in S. mutans fimbria preparations from CS subjects than in those from CR individuals. For example, four of six fimbria preparations from CS patients had demonstrable P1, and all had GTF. In contrast, only two of five CR fimbrial preparations exhibited P1 and GTF. Enzyme-linked immunosorbent assay demonstrated similar results for levels of GTF antigen in the fimbrial preparations from CR and CS subjects. The results suggest that differences between the compositions of S. mutans fimbriae in CR and CS individuals may play an important role in the virulence of this microorganism in dental caries.
PMCID: PMC170521  PMID: 9144366
8.  A Feasible Enzyme-Linked Immunosorbent Assay System Using Monoclonal and Polyclonal Antibodies Against Glucosyltransferase-B from Streptococcus mutans 
Hybridoma  2012;31(3):176-179.
Streptococcus mutans
has been considered the principal etiological agent of dental caries in humans. S. mutans can secrete three kinds of glucosyltransferases (GTFs). One of these, GTF-B, which synthesizes water-insoluble glucans from sucrose, has been considered to be one of the most important factors of cariogenic dental plaque formation. Therefore, determination of whether GTF-B is present in plaque and saliva samples may contribute to the evaluation of individual virulence potential (caries risk). The aim of this study was to develop a feasible enzyme-linked immunosorbent assay (ELISA) for the routine quantification of GTF-B in plaque-derived cultures and clinical samples, and to apply this assay to an epidemiological study. To determine the presence of GTF-B in plaque samples, a sandwich-ELISA was devised, consisting of mouse monoclonal and rabbit polyclonal antibodies against GTF-B and a horseradish peroxidase-conjugated anti-rabbit antibody. The developed ELISA allowed for quantification of the amounts of purified GTF-B with satisfactory sensitivity and specificity; this method was not affected by other components such as plaque and saliva. Plaque samples from healthy volunteers were examined using this ELISA method and microbial analysis to apply the assay to an epidemiological study. A correlation was observed between the amount of extracted GTF-B and S. mutans levels as determined by ELISA and cultivated with Mitis Salivarius Bacitracin agar plates derived from plaque samples, although there were some exceptions. In this regard, this ELISA system has the advantage of estimating both the individual numbers of S. mutans and the productivity of GTF-B, namely, the cariogenic potential of S. mutans simultaneously. These results indicate that this ELISA method is a useful tool for the diagnosis of caries risk.
PMCID: PMC3385998  PMID: 22741581
9.  Oral passive immunization against dental caries in rats by use of hen egg yolk antibodies specific for cell-associated glucosyltransferase of Streptococcus mutans. 
Infection and Immunity  1991;59(11):4161-4167.
The effect of polyclonal egg yolk immunoglobulin G antibodies (yIgG) raised against whole cells, cell-free (CF) glucosyltransferase (GTase), or cell-associated (CA) GTase of serotype c Streptococcus mutans was examined in terms of in vitro inhibition of virulence-related factors of S. mutans and protection of S. mutans-infected rats against the development of dental caries. Hens (18 weeks old) were immunized with formalin-treated whole cells, purified CF-GTase, or CA-GTase together with Freund's complete adjuvant. In addition, yIgG to surface protein antigen was used in some in vitro experiments for comparison with other antibodies. yIgG was purified by ammonium sulfate precipitation followed by DEAE-Sephacel column chromatography or fractional precipitation with ethanol. Purified yIgG was found to be a 220-kDa protein, which was dissociated into heavy and light chains upon addition of 2-mercaptoethanol. yIgG to whole cells and surface protein antigen gave a heavy aggregation of S. mutans organisms, while yIgG to CF- and CA-GTase specifically inhibited the enzymatic activity of the respective GTase. yIgG to CA-GTase and whole cells was found to clearly suppress the adherence of S. mutans cells to a glass surface. Specific-pathogen-free Sprague-Dawley rats that had been infected heavily and repeatedly with S. mutans and fed diet no. 2000 developed severe dental caries, while rats fed diet 2000 containing greater than or equal to 0.1% yIgG to CA-GTase showed a statistically significant reduction in dental plaque accumulation and caries development. Administration of yIgG to CF-GTase and whole cells failed to protect against caries. These results clearly suggest that yIgG to S. mutants CA-GTase specifically inhibited a virulence factor of this organism, i.e., insoluble glucan-synthesizing CA-GTase, resulting in a significant reduction in the development of dental caries.
PMCID: PMC259011  PMID: 1834573
10.  Phylogenetic Analysis of Glucosyltransferases and Implications for the Coevolution of Mutans Streptococci with Their Mammalian Hosts 
PLoS ONE  2013;8(2):e56305.
Glucosyltransferases (Gtfs) catalyze the synthesis of glucans from sucrose and are produced by several species of lactic-acid bacteria. The oral bacterium Streptococcus mutans produces large amounts of glucans through the action of three Gtfs. GtfD produces water-soluble glucan (WSG), GtfB synthesizes water-insoluble glucans (WIG) and GtfC produces mainly WIG but also WSG. These enzymes, especially those synthesizing WIG, are of particular interest because of their role in the formation of dental plaque, an environment where S. mutans can thrive and produce lactic acid, promoting the formation of dental caries. We sequenced the gtfB, gtfC and gtfD genes from several mutans streptococcal strains isolated from the oral cavity of humans and searched for their homologues in strains isolated from chimpanzees and macaque monkeys. The sequence data were analyzed in conjunction with the available Gtf sequences from other bacteria in the genera Streptococcus, Lactobacillus and Leuconostoc to gain insights into the evolutionary history of this family of enzymes, with a particular emphasis on S. mutans Gtfs. Our analyses indicate that streptococcal Gtfs arose from a common ancestral progenitor gene, and that they expanded to form two clades according to the type of glucan they synthesize. We also show that the clade of streptococcal Gtfs synthesizing WIG appeared shortly after the divergence of viviparous, dentate mammals, which potentially contributed to the formation of dental plaque and the establishment of several streptococci in the oral cavity. The two S. mutans Gtfs capable of WIG synthesis, GtfB and GtfC, are likely the product of a gene duplication event. We dated this event to coincide with the divergence of the genomes of ancestral early primates. Thus, the acquisition and diversification of S. mutans Gtfs predates modern humans and is unrelated to the increase in dietary sucrose consumption.
PMCID: PMC3572963  PMID: 23457545
11.  Mutagenesis of Asp-569 of Glucosyltransferase I Glucansucrase Modulates Glucan and Oligosaccharide Synthesis 
Glucansucrases of oral streptococci and Leuconostoc mesenteroides are enzymes of medical and biotechnological interest that synthesize α-glucans. They can also synthesize oligosaccharides in the presence of a sugar acceptor. Previous reports have identified an amino acid residue that may affect the structure of the glucan product; therefore, random mutagenesis of the corresponding Asp-569 of Streptococcus downei glucosyltransferase I (GTF-I) was used to further understanding of its involvement in the catalytic mechanism and to evaluate how different amino acids can modulate glucan and oligosaccharide synthesis. GTF-I variants were obtained where Asp-569 was replaced by each of the different possible classes of amino acids. These were expressed in Escherichia coli and purified by means of a His6 tag. The results showed that the amino acid in position 569 influences the structure of the glucan and the size of the oligosaccharides produced by GTF-I. The results suggest that the amino acid occupying this position is more likely to interact with the acceptor molecules (oligosaccharides or elongating glucan chain) than to be directly involved in glucosyl transfer from sucrose. Engineering of the equivalent position in glucansucrases thus appears to be a good target to expand the range of oligosaccharides synthesized.
PMCID: PMC101434  PMID: 10788361
12.  Biology of Streptococcus mutans-Derived Glucosyltransferases: Role in Extracellular Matrix Formation of Cariogenic Biofilms 
Caries Research  2011;45(1):69-86.
The importance of Streptococcus mutans in the etiology and pathogenesis of dental caries is certainly controversial, in part because excessive attention is paid to the numbers of S. mutans and acid production while the matrix within dental plaque has been neglected. S. mutans does not always dominate within plaque; many organisms are equally acidogenic and aciduric. It is also recognized that glucosyltransferases from S. mutans (Gtfs) play critical roles in the development of virulent dental plaque. Gtfs adsorb to enamel synthesizing glucans in situ, providing sites for avid colonization by microorganisms and an insoluble matrix for plaque. Gtfs also adsorb to surfaces of other oral microorganisms converting them to glucan producers. S. mutans expresses 3 genetically distinct Gtfs; each appears to play a different but overlapping role in the formation of virulent plaque. GtfC is adsorbed to enamel within pellicle whereas GtfB binds avidly to bacteria promoting tight cell clustering, and enhancing cohesion of plaque. GtfD forms a soluble, readily metabolizable polysaccharide and acts as a primer for GtfB. The behavior of soluble Gtfs does not mirror that observed with surface-adsorbed enzymes. Furthermore, the structure of polysaccharide matrix changes over time as a result of the action of mutanases and dextranases within plaque. Gtfs at distinct loci offer chemotherapeutic targets to prevent caries. Nevertheless, agents that inhibit Gtfs in solution frequently have a reduced or no effect on adsorbed enzymes. Clearly, conformational changes and reactions of Gtfs on surfaces are complex and modulate the pathogenesis of dental caries in situ, deserving further investigation.
PMCID: PMC3068567  PMID: 21346355
Biofilms; Dental caries; Extracellular matrix; Glucosyltransferases; Polysaccharides; Streptococcus mutans
13.  Expression, crystallization and preliminary X-ray analysis of the phosphoribosylglycinamide formyltransferase from Streptococcus mutans  
Phosphoribosylglycinamide formyltransferase (PurN) from Streptococcus mutans was expressed in E. coli, purified and studied crystallographically.
Phosphoribosylglycinamide formyltransferase (PurN) from Streptococcus mutans was recombinantly expressed in Escherichia coli. An effective purification protocol was established. The purified protein, which had a purity of >95%, was identified by SDS–PAGE and MALDI–TOF MS. The protein was crystallized using the vapour-diffusion method in hanging-drop mode with PEG 3350 as the primary precipitant. X-ray diffraction data were collected to 2.1 Å resolution. Preliminary X-ray analysis indicated that the crystal belonged to space group P212121, with unit-cell parameters a = 52.25, b = 63.29, c = 131.81 Å.
PMCID: PMC3034630  PMID: 21301108
Streptococcus mutans; PurN; phosphoribosylglycinamide formyltransferases
14.  4,6-α-Glucanotransferase, a Novel Enzyme That Structurally and Functionally Provides an Evolutionary Link between Glycoside Hydrolase Enzyme Families 13 and 70▿ 
Applied and Environmental Microbiology  2011;77(22):8154-8163.
Lactobacillus reuteri 121 uses the glucosyltransferase A (GTFA) enzyme to convert sucrose into large amounts of the α-d-glucan reuteran, an exopolysaccharide. Upstream of gtfA lies another putative glucansucrase gene, designated gtfB. Previously, we have shown that the purified recombinant GTFB protein/enzyme is inactive with sucrose. Various homologs of gtfB are present in other Lactobacillus strains, including the L. reuteri type strain, DSM 20016, the genome sequence of which is available. Here we report that GTFB is a novel α-glucanotransferase enzyme with disproportionating (cleaving α1→4 and synthesizing α1→6 and α1→4 glycosidic linkages) and α1→6 polymerizing types of activity on maltotetraose and larger maltooligosaccharide substrates (in short, it is a 4,6-α-glucanotransferase). Characterization of the types of compounds synthesized from maltoheptaose by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS), methylation analysis, and 1-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy revealed that only linear products were made and that with increasing degrees of polymerization (DP), more α1→6 glycosidic linkages were introduced into the final products, ranging from 18% in the incubation mixture to 33% in an enriched fraction. In view of its primary structure, GTFB clearly is a member of the glycoside hydrolase 70 (GH70) family, comprising enzymes with a permuted (β/α)8 barrel that use sucrose to synthesize α-d-glucan polymers. The GTFB enzyme reaction and product specificities, however, are novel for the GH70 family, resembling those of the GH13 α-amylase type of enzymes in using maltooligosaccharides as substrates but differing in introducing a series of α1→6 glycosidic linkages into linear oligosaccharide products. We conclude that GTFB represents a novel evolutionary intermediate between the GH13 and GH70 enzyme families, and we speculate about its origin.
PMCID: PMC3209003  PMID: 21948833
15.  Crystallization and preliminary X-ray analysis of S-­ribosylhomocysteinase from Streptococcus mutans  
S-Ribosylhomocysteinase (LuxS) encoded by the LuxS gene from Streptococcus mutans was solubly expressed in Escherichia coli, purified and crystallized. Diffraction by the crystal extended to 2.4 Å resolution.
S-Ribosylhomocysteinase (LuxS) encoded by the luxS gene from Streptococcus mutans plays a crucial role in the quorum-sensing system. LuxS was solubly expressed in Escherichia coli with high yield. The purity of the purified target protein, which was identified by SDS–PAGE and MALDI–TOF MS analysis, was >95%. The protein was crystallized using the hanging-drop vapour-diffusion method with PEG 3350 as the primary precipitant. X-ray diffraction data were collected at Beijing Synchrotron Radiation Facility (BSRF). Diffraction by the crystal extended to 2.4 Å resolution and the crystal belonged to space group C2221, with unit-cell parameters a = 55.3, b = 148.7, c = 82.8 Å.
PMCID: PMC3274403  PMID: 22297999
Streptococcus mutans; LuxS
16.  Interaction of Salivary alpha-Amylase and Amylase-Binding-Protein A (AbpA) of Streptococcus gordonii with Glucosyltransferase of S. gordonii and Streptococcus mutans 
BMC Microbiology  2007;7:60.
Glucosyltransferases (Gtfs), enzymes that produce extracellular glucans from dietary sucrose, contribute to dental plaque formation by Streptococcus gordonii and Streptococcus mutans. The alpha-amylase-binding protein A (AbpA) of S. gordonii, an early colonizing bacterium in dental plaque, interacts with salivary amylase and may influence dental plaque formation by this organism. We examined the interaction of amylase and recombinant AbpA (rAbpA), together with Gtfs of S. gordonii and S. mutans.
The addition of salivary alpha-amylase to culture supernatants of S. gordonii precipitated a protein complex containing amylase, AbpA, amylase-binding protein B (AbpB), and the glucosyltransferase produced by S. gordonii (Gtf-G). rAbpA was expressed from an inducible plasmid, purified from Escherichia coli and characterized. Purified rAbpA, along with purified amylase, interacted with and precipitated Gtfs from culture supernatants of both S. gordonii and S. mutans. The presence of amylase and/or rAbpA increased both the sucrase and transferase component activities of S. mutans Gtf-B. Enzyme-linked immunosorbent assay (ELISA) using anti-Gtf-B antibody verified the interaction of rAbpA and amylase with Gtf-B. A S. gordonii abpA-deficient mutant showed greater biofilm growth under static conditions than wild-type in the presence of sucrose. Interestingly, biofilm formation by every strain was inhibited in the presence of saliva.
The results suggest that an extracellular protein network of AbpA-amylase-Gtf may influence the ecology of oral biofilms, likely during initial phases of colonization.
PMCID: PMC3225810  PMID: 17593303
17.  Expression, purification and preliminary X-ray diffraction analysis of the catalytic module of a β-­agarase from the flavobacterium Zobellia galactanivorans  
A novel family GH16 β-agarase from the marine bacterium Zobellia galactanivorans was expressed, purified and crystallized. Hexagonal crystals belonging to space group P3121 diffracted to 2.2 Å resolution, whereas orthorhombic crystals belonging to space group P212121 diffracted to 1.5–Å resolution.
Marine bacteria secrete specific glycoside hydrolases such as agarases to access polysaccharides from algal cell walls as a carbon and energy source. In an attempt to identify agarases with variable degradation patterns, a novel family GH16 β-agarase from the marine bacterium Zobellia galactanivorans was expressed, purified and crystallized. The purified enzyme crystallized in two distinct forms that were grown by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. Hexagonal crystals belonging to space group P3121 diffracted to 2.2 Å resolution, whereas orthorhombic crystals belonging to space group P212121 diffracted to 1.5 Å resolution.
PMCID: PMC2852333  PMID: 20383011
β-agarases; glycoside hydrolases; heterologous expression; Zobellia galactanivorans
18.  Biofilm formation and virulence expression by Streptococcus mutans are altered when grown in dual-species model 
BMC Microbiology  2010;10:111.
Microbial cell-cell interactions in the oral flora are believed to play an integral role in the development of dental plaque and ultimately, its pathogenicity. The effects of other species of oral bacteria on biofilm formation and virulence gene expression by Streptococcus mutans, the primary etiologic agent of dental caries, were evaluated using a dual-species biofilm model and RealTime-PCR analysis.
As compared to mono-species biofilms, biofilm formation by S. mutans was significantly decreased when grown with Streptococcus sanguinis, but was modestly increased when co-cultivated with Lactobacillus casei. Co-cultivation with S. mutans significantly enhanced biofilm formation by Streptococcus oralis and L. casei, as compared to the respective mono-species biofilms. RealTime-PCR analysis showed that expression of spaP (for multi-functional adhesin SpaP, a surface-associated protein that S. mutans uses to bind to the tooth surface in the absence of sucrose), gtfB (for glucosyltransferase B that synthesizes α1,6-linked glucan polymers from sucrose and starch carbohydrates) and gbpB (for surface-associated protein GbpB, which binds to the glucan polymers) was decreased significantly when S. mutans were co-cultivated with L. casei. Similar results were also found with expression of spaP and gbpB, but not gtfB, when S. mutans was grown in biofilms with S. oralis. Compared to mono-species biofilms, the expression of luxS in S. mutans co-cultivated with S. oralis or L. casei was also significantly decreased. No significant differences were observed in expression of the selected genes when S. mutans was co-cultivated with S. sanguinis.
These results suggest that the presence of specific oral bacteria differentially affects biofilm formation and virulence gene expression by S. mutans.
PMCID: PMC2867949  PMID: 20398271
19.  Crystallization and preliminary X-ray crystallographic analysis of SMU.412c protein from the caries pathogen Streptococcus mutans  
Crystallization of SMU.412c protein from the caries pathogen Streptococcus mutans can easily appear in the condition 2.8 M sodium acetate pH 7.0 and its crystal belongs to space group P41212.
The smu.412c gene encodes a putative histidine triad-like protein (SMU.412c) with 139 residues that is involved in cell-cycle regulation in Streptococcus mutans. The gene was cloned into the expression vector pET28a and subsequently expressed in Escherichia coli strain BL21 (DE3) to give a substantially soluble form of SMU.412c with a His6 tag at its N-terminus. The recombinant protein was purified to homogeneity in a two-step procedure involving Ni2+-chelating and size-exclusion chromatography. Crystals suitable for X-ray diffraction were obtained using the sitting-drop vapour-diffusion method and diffracted to 1.8 Å resolution on beamline BL6A at Photon Factory, Tsukuba, Japan. The crystal belonged to space group P41212, with unit-cell parameters a = b = 53.5, c = 141.1 Å.
PMCID: PMC2664769  PMID: 19342789
SMU.412c; dental caries; Streptococcus mutans; histidine triad-like proteins
20.  Expression, purification, crystallization and preliminary X-ray analysis of Aeromonas hydrophilia metallo-β-lactamase 
Crystallization and preliminary X-ray analysis of the CphA metallo-β-lactamase from A. hydrophilia are described. The crystals belonged to space group P21212, with unit-cell parameters a = 40.75, b = 42.05, c = 128.88 Å, and diffract to 1.8 Å.
The CphA metallo-β-lactamase from Aeromonas hydrophilia has been expressed, purified and crystallized by the hanging-drop vapor-diffusion method using ammonium sulfate as the precipitant. The crystals exhibit orthorhombic symmetry (P21212), with unit-cell parameters a = 40.75, b = 42.05, c = 128.88 Å. There is one monomer in the asymmetric unit and the solvent content is estimated to be 44% by volume. A data set extending to 1.8 Å has been measured.
PMCID: PMC1952252  PMID: 16510987
metallo-β-lactamases; Aeromonas hydrophilia
21.  Streptococcus gordonii’s Sequenced Strain CH1 Glucosyltransferase Determines Persistent But Not Initial Colonization of Teeth of Rats 
Archives of oral biology  2007;53(2):133-140.
Extracellular glucan synthesis from sucrose by Streptococcus gordonii, a major dental plaque biofilm bacterium, is assumed important for colonization of teeth; but this hypothesis is un-tested in vivo.
To do so, we studied an isogenic glucosyltransferase (Gtf)-negative mutant (strain AMS12, gtfG−) of S. gordonii sequenced wild type (WT, strain Challis CH1, gtfG+), comparing their in vitro abilities to grow in the presence of glucose and sucrose and, in vivo, to colonize and persist on teeth and induce caries in rats. Weanling rats of two breeding colonies, TAN:SPFOM(OM)BR and TAN:SPFOM(OMASF)BR, eating high sucrose diet, were inoculated with either the WT (gtfG+), its isogenic gtfG− mutant, or reference strains of Streptococcus mutans. Control animals were not inoculated.
In vitro, the gtfG− strain grew at least as rapidly in the presence of sucrose as its WT gtfG+ progenitor, but formed soft colonies on sucrose agar, consistent with its lack of insoluble glucan synthesis. It also had a higher growth yield due apparently to its inability to channel carbon flow into extracellular glucan. In vivo, the gtfG− mutant initially colonized as did the WT as but, unlike the WT, failed to persist on the teeth as shown over time. By comparison to three S. mutans strains, S. gordonii WT, despite its comparable ecological success on the teeth, was associated with only modest caries induction. Failure of the gtfG− mutant to persistently colonize was associated with slight diminution of caries scores by comparison with its gtfG+ WT.
Initial S. gordonii colonization does not depend on Gtf-G synthesis; rather, Gtf-G production determines S. gordonii’s ability to persist on the teeth of sucrose-fed rats. S. gordonii appears weakly cariogenic by comparison with S. mutans reference strains.
PMCID: PMC2243221  PMID: 17961499
S. gordonii; glucosyltransferase; colonization persistence; biofilm; plaque; dental caries
22.  Influence of Cranberry Proanthocyanidins on Formation of Biofilms by Streptococcus mutans on Saliva-Coated Apatitic Surface and on Dental Caries Development in vivo 
Caries Research  2010;44(2):116-126.
Cranberry crude extracts, in various vehicles, have shown inhibitory effects on the formation of oral biofilms in vitro. The presence of proanthocyanidins (PAC) in cranberry extracts has been linked to biological activities against specific virulence attributes of Streptococcus mutans, e.g. the inhibition of glucosyltransferase (Gtf) activity. The aim of the present study was to determine the influence of a highly purified and chemically defined cranberry PAC fraction on S. mutans biofilm formation on saliva-coated hydroxyapatite surface, and on dental caries development in Sprague-Dawley rats. In addition, we examined the ability of specific PAC (ranging from low-molecular-weight monomers and dimers to high-molecular-weight oligomers/polymers) to inhibit GtfB activity and glycolytic pH drop by S. mutans cells, in an attempt to identify specific bioactive compounds. Topical applications (60-second exposure, twice daily) with PAC (1.5 mg/ml) during biofilm formation resulted in less biomass and fewer insoluble polysaccharides than the biofilms treated with vehicle control had (10% ethanol, v/v; p < 0.05). The incidence of smooth-surface caries in rats was significantly reduced by PAC treatment (twice daily), and resulted in less severe carious lesions compared to the vehicle control group (p < 0.05); the animals treated with PAC also showed significantly less caries severity on sulcal surfaces (p < 0.05). Furthermore, specific A-type PAC oligomers (dimers to dodecamers; 0.1 mg/ml) effectively diminished the synthesis of insoluble glucans by GtfB adsorbed on a saliva-coated hydroxyapatite surface, and also affected bacterial glycolysis. Our data show that cranberry PAC reduced the formation of biofilms by S. mutans in vitro and dental caries development in vivo, which may be attributed to the presence of specific bioactive A-type dimers and oligomers.
PMCID: PMC2883842  PMID: 20234135
Biofilm; Cranberry; Dental caries; Extracellular matrix; Glucans; Glucosyltransferases; Proanthocyanidins
23.  Protein preparation and preliminary X-ray crystallographic analysis of a putative glucosamine 6-phosphate deaminase from Streptococcus mutants  
A glucosamine 6-phosphate deaminase homologue from S. mutans was expressed, purified and crystallized. Diffraction data have been collected to 2.4 Å resolution.
The SMU.636 protein from Streptococcus mutans is a putative glucosamine 6-­phosphate deaminase with 233 residues. The smu.636 gene was PCR-amplified from S. mutans genomic DNA and cloned into the expression vector pET-28a(+). The resultant His-tagged fusion protein was expressed in Escherichia coli and purified to homogeneity in two steps. Crystals of the fusion protein were obtained by the hanging-drop vapour-diffusion method. The crystals diffracted to 2.4 Å resolution and belong to space group P212121, with unit-cell parameters a = 53.83, b = 82.13, c = 134.70 Å.
PMCID: PMC2376312  PMID: 17768362
SMU.636; Streptococcus mutans;  glucosamine 6-­phosphate deaminase
24.  Symbiotic Relationship between Streptococcus mutans and Candida albicans Synergizes Virulence of Plaque Biofilms In Vivo 
Infection and Immunity  2014;82(5):1968-1981.
Streptococcus mutans is often cited as the main bacterial pathogen in dental caries, particularly in early-childhood caries (ECC). S. mutans may not act alone; Candida albicans cells are frequently detected along with heavy infection by S. mutans in plaque biofilms from ECC-affected children. It remains to be elucidated whether this association is involved in the enhancement of biofilm virulence. We showed that the ability of these organisms together to form biofilms is enhanced in vitro and in vivo. The presence of C. albicans augments the production of exopolysaccharides (EPS), such that cospecies biofilms accrue more biomass and harbor more viable S. mutans cells than single-species biofilms. The resulting 3-dimensional biofilm architecture displays sizeable S. mutans microcolonies surrounded by fungal cells, which are enmeshed in a dense EPS-rich matrix. Using a rodent model, we explored the implications of this cross-kingdom interaction for the pathogenesis of dental caries. Coinfected animals displayed higher levels of infection and microbial carriage within plaque biofilms than animals infected with either species alone. Furthermore, coinfection synergistically enhanced biofilm virulence, leading to aggressive onset of the disease with rampant carious lesions. Our in vitro data also revealed that glucosyltransferase-derived EPS is a key mediator of cospecies biofilm development and that coexistence with C. albicans induces the expression of virulence genes in S. mutans (e.g., gtfB, fabM). We also found that Candida-derived β1,3-glucans contribute to the EPS matrix structure, while fungal mannan and β-glucan provide sites for GtfB binding and activity. Altogether, we demonstrate a novel mutualistic bacterium-fungus relationship that occurs at a clinically relevant site to amplify the severity of a ubiquitous infectious disease.
PMCID: PMC3993459  PMID: 24566629
25.  Experimental immunization of rats with a Streptococcus mutans 59-kilodalton glucan-binding protein protects against dental caries. 
Infection and Immunity  1996;64(8):3069-3073.
Glucan-binding proteins (GBPs) are theoretically important in the molecular pathogenesis of dental caries caused by Streptococcus mutans. The present study evaluated the ability of antibody induced by the S. mutans 59-kDa GBP (GBP59) to affect dental caries caused by experimental infection with S. mutans in a rodent model. Groups of 20-day-old rats were injected twice at 9-day intervals subcutaneously in the salivary gland vicinity with GBP59, glucosyltransferase (GTF), or phosphate-buffered saline (sham injection), each incorporated in an adjuvant. Two weeks after the second injection, GBP59- and GTF-injected rats contained significant levels of salivary immunoglobulin A and serum immunoglobulin G antibody to the respective injected antigens. However, cross-reacting antibody to S. mutans GTF or GBP59 was not induced by the respective antigen. Rats were then orally infected with S. mutans. After 71 days of infection, GBP59- and GTF-injected groups had smaller numbers of S. mutans on their molar surfaces, compared with the sham-injected infected group. Total, sulcal, and smooth-surface molar caries in the GBP59- and GTF-immunized S. mutans-infected groups were each significantly lower (P < or = 0.003) than the respective measures of caries in the sham injected infected group. The results of this investigation demonstrate that immunization with S. mutans GBP59 induces an immune response in rats that can interfere with the accumulation of S. mutans and can reduce the level of dental caries caused by this cariogenic streptococcus. Furthermore, the protective immunity induced by either GBP59 or GTF appears to result from antibodies to independent epitopes since these two S. mutans components do not have a close antigenic relationship.
PMCID: PMC174189  PMID: 8757835

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