Identification of Streptococcus mutans PAc peptide motif binding with human MHC class II molecules (DRB1*0802, *1101, *1401 and *1405)

KATSUMATA et al.Comprehensive characterization of sortase A-dependent surface proteins in Streptococcus mutansComprehensive characterization of sortase A-dependent surface proteins in Streptococcus mutans

Streptococcus mutans, a cariogenic pathogen, adheres to the tooth surface and forms a biofilm. Bacterial cell surface proteins are associated with adherence to substrates. Sortase A (SrtA) mediates the localization of proteins with an LPXTG motif-containing proteins to the cell surface by covalent binding to peptidoglycan. In S. mutans UA159, 6 SrtA-dependent proteins, SpaP, WapA, WapE, DexA, FruA, and GbpC, were identified. Although some of these proteins were characterized, a comprehensive analysis of the 6 proteins has not been reported. In this study, we constructed mutants deficient in each of these proteins and the SrtA-deficient mutant. The SrtA-deficient mutant showed drastically decreased binding to salivary components, biofilm formation, bacterial coaggregation activity, hydrophobicity, and cellular matrix binding (collagen type I, fibronectin, and laminin). The SpaP-deficient mutant showed significantly reduced binding to salivary components and partially increased coaggregation with Porphyromonas gingivalis, and decreased hydrophobicity, and collagen binding. The WapA-deficient mutant showed slightly decreased coaggregation with Fusobacterium nucleatum. Although the SrtA-deficient mutant showed drastically altered phenotypes, all SrtA-dependent protein-deficient mutants, except the SpaP-deficient mutant, did not show considerable alterations in binding to salivary components. These results indicate that the 6 proteins may coordinately contribute to these activities. In addition, using genomic data of 125 S. mutans strains, we compared the amino acid sequences of each surface protein and found many variations among strains, which may affect the phenotype of cell surface proteins in S. mutans. This article is protected by copyright. All rights reserved.

The changing faces of Streptococcus antigen I/II polypeptide family adhesins

Streptococcus mutans antigen I/II (AgI/II) protein was one of the first cell wall-anchored adhesins identified in Gram-positive bacteria. It mediates attachment of S. mutans to tooth surfaces and has been a focus for immunization studies against dental caries. The AgI/II family polypeptides recognize salivary glycoproteins, and are also involved in biofilm formation, platelet aggregation, tissue invasion and immune modulation. The genes encoding AgI/II family polypeptides are found among Streptococcus species indigenous to the human mouth, as well as in Streptococcus pyogenes, S. agalactiae and S. suis. Evidence of functionalities for different regions of the AgI/II proteins has emerged. A sequence motif within the C-terminal portion of Streptococcus gordonii SspB (AgI/II) is bound by Porphyromonas gingivalis, thus promoting oral colonization by this anaerobic pathogen. The significance of other epitopes is now clearer following resolution of regional crystal structures. A new picture emerges of the central V (variable) region, predicted to contain a carbohydrate-binding trench, being projected from the cell surface by a stalk formed by an unusual association between an N-terminal alpha-helix and a C-terminal polyproline helix. This presentation mode might be important in determining functional conformations of other Gram-positive surface proteins that have adhesin domains flanked by alpha-helical and proline-rich regions.

Induction of neutralizing antibodies in mice immunized with an amino-terminal polypeptide of Streptococcus mutans P1 protein produced by a recombinant Bacillus subtilis strain

The oral pathogen Streptococcus mutans expresses a surface protein, P1, which interacts with the salivary pellicle on the tooth surface or with fluid-phase saliva, resulting in bacterial adhesion or aggregation, respectively. P1 is a target of protective immunity. Its N-terminal region has been associated with adhesion and aggregation functions and contains epitopes recognized by efficacious antibodies. In this study, we used Bacillus subtilis, a gram-positive expression host, to produce a recombinant N-terminal polypeptide of P1 (P1(39-512)) derived from the S. mutans strain UA159. Purified P1(39-512) reacted with an anti-full-length P1 antiserum as well as one raised against intact S. mutans cells, indicating preserved antigenicity. Immunization of mice with soluble and heat-denatured P1(39-512) induced antibodies that reacted specifically with native P1 on the surface of S. mutans cells. The anti-P1(39-512) antiserum was as effective at blocking saliva-mediated aggregation of S. mutans cells and better at blocking bacterial adhesion to saliva-coated plastic surfaces compared with the anti-full-length P1 antiserum. In addition, adsorption of the anti-P1 antiserum with P1(39-512) eliminated its ability to block the adhesion of S. mutans cells to abiotic surfaces. The present results indicate that P1(39-512), expressed and purified from a recombinant B. subtilis strain, maintains important immunological features of the native protein and represents an additional tool for the development of anticaries vaccines.

The role of anti-PAc (361-386) peptide SIgA antibody in professional oral hygiene of the elderly

OBJECTIVE

Measurement of salivary IgA antibody (PAc-peptide antibody, PPA) to amino acid residues 361-386 of Streptococcus mutans PAc, which possess a multiple binding motif to various HLA-DR molecules and a B-cell epitope that recognises the inhibiting antibody to S. mutans, is an indicator for the population numbers of mutans streptococci (MS) in human saliva. The purpose of this study was to clarify the role of PPA in infection control of MS after professional oral hygiene care.

MATERIALS AND METHODS

Thirty-nine dependently living institutionalised elderly subjects (75.9 +/- 7.5 years; 10 males, 29 females) participated in the study. The measurements of PPA, MS, total streptococci (TS) and lactobacilli (LB) were performed by ELISA and culture techniques from saliva, plaque and tongue samples from the elderly.

RESULTS

After treatment using professional oral care, the numbers of MS decreased significantly at 6 months in saliva and tongue samples from the group not having PPA in comparison with the primary data; whereas in the PPA-detected group, a significant decrease in MS number was shown immediately following professional care at 1-12 months in all samples. There was little difference in the numbers of LB at any of the time points. The numbers of TS decreased rapidly in PPA-not detected group in comparison with the PPA-detected group.

CONCLUSION

PPA may be more effective for controlling MS number in the oral cavity after professional treatment. The measurement of PPA may be used for preventive instruction to dental caries at the chair side in the clinical setting.

Relationships of anti-PAc (361-386) peptide salivary IgA antibody, eosinophils and basophils with periodontal status in the elderly

The amino acid residues 361-386 of Streptococcus mutans PAc includes an important region associated with the interaction between S. mutans and salivary components. We investigated the relationships between levels of the anti-PAc (361-386) peptide antibody (PPA) in saliva and periodontal status in 281 elderly subjects (mean age 77 years; 118 females, 163 males) by assessing dental calculus (CA), attachment loss (AL), pocket depth (PD), bleeding on probing (BOP) and various blood parameters. Enzyme-linked immunosorbent assay results revealed that subjects with a PPA level of greater than 0.1 (PPA detected group) showed a lower average value for number of sites with more than 6 mm of AL/6 points x 100/tooth (rAL6) than those with a PPA level of less than 0.1 (PPA not detected group). Furthermore, average values for rAL6 were significantly lower in the PPA detected group, and BOP, AL and rAL6 correlated positively and significantly with the percentage of eosinophils present in leukocytes in female subjects in both groups. PPA level had a negative correlation with percentages of basophils and eosinophils. The results indicate that systemic increases in numbers of eosinophils and basophils are associated with the development of periodontal diseases, while PPA level may be a useful indicator of periodontal status.

Low salivary IgA activity to cell-surface antigens of mutans streptococci related to HLA-DRB1*04

BACKGROUND/AIMS

Mutans streptococci are found in almost all individuals, though there are large differences in colonization levels between individuals. These differences are not readily explained, though several factors are believed to influence the colonization. One factor is the immune response to mutans streptococci, mainly provided by salivary immunoglobulin A (IgA). In a previous study, differences in salivary IgA reactions to oral streptococci were observed between human leukocyte antigen (HLA)-DR4-positive and DR4-negative individuals. A lower salivary IgA activity to Streptococcus mutans in particular was most pronounced for two DR4 subgroups, DRB1*0401 and *0404. The main purpose of this study was to further investigate, in a larger study group, the salivary IgA activity to antigens of three oral streptococci in relation to different HLA-DRB1*04 alleles.

METHODS

Stimulated saliva was collected from 58 HLA-DRB1*04-positive individuals. Whole cell antigen extracts from S. mutans, Streptococcus sobrinus and Streptococcus parasanguis and the streptococcal antigen (SA) I/II were separated in SDS-PAGE, transblotted and detected with diluted saliva (Western blot), and analyzed in a computer program. All distinct immunoblot bands over 100 kDa were recorded and compared in relation to DRB1*04.

RESULTS

The immunoblots revealed lower salivary IgA reactions to S. mutans, S. sobrinus and SA I/II, but not to S. parasanguis, for the DRB1*0401- and *0404-positive individuals compared to other DRB1*04 types. For the *0401 subgroup there was a significant association with a lower IgA response to S. mutans.

CONCLUSION

The results confirm earlier observations and may also support previous demonstrated association between colonization by mutans streptococci and the serologically defined HLA-DR4.

Role of peptide antigen for induction of inhibitory antibodies to Streptococcus mutans in human oral cavity

The alanine-rich repeating region (A-region) in the surface protein antigen (PAc) of Streptococcus mutans has received much attention as an antigenic component for vaccines against dental caries. The PAc (residue 361-386) peptide in the A-region possesses a multiple binding motif (L- -V-K- -A) to various HLA-DR molecules and a B-cell core epitope (- Y- - -L- -Y- - - -) that recognizes the inhibiting antibody to S. mutans. In the present study, we investigated the immunogenicity of the PAc (361-386) peptide in humans and regulators of induction of the anti-PAc (361-386) peptide IgA antibody (aPPA) in saliva. The PAc (361-386) peptide was confirmed as an ideal peptide antigen for induction of the inhibiting antibody to S. mutans in 151 healthy human subjects (36.6 +/- 12.6 years old) by quantitative analyses of oral bacteria and ELISA, as the aPPA titre in human saliva decreased significantly in an age-dependent manner. Homozygous DRB1*0405 and 1502, and heterozygous DRB1*0405/1502 showed a negative association with production of aPPA and tended to reduce the number of total streptococci in saliva. In contrast, the DRB1*1501 allele was significantly correlated with a high level of induction of the antibodies, and also tended to reduce lactobacilli and mutans streptococci. Further, peptide immunogenicity was confirmed in NOD-SCID mice grafted with human peripheral blood mononuclear cells. Our results indicate that the interplay between regulators such as age, DRB1 genotype, cytokines, and peptide immunogenicity may provide a potential means for developing a vaccine useful for the prevention of dental caries as well as their diagnosis.

Identification of the peptide motifs that interact with HLA-DR8 (DRB1*0802) in Streptococcus mutans proteins

A glucosyltransferase (GTF) and a surface protein antigen (PAc) of Streptococcus mutans have been suggested as possible components of an effective dental caries vaccine. To identify antigenic peptides in GTF and PAc that bind to MHC class II (HLA-DR8, DRB1*0802) molecules, we investigated binding activities to DR8 molecules of overlapping synthetic peptides at several sites in GTF and in the alanine-rich repeating region of PAc using an ELISA-inhibition competitive binding assay for the interaction between the HLA-DR molecule and the PAc (316-334) peptide. Six GTF peptides and 10 PAc peptides strongly bound to the HLA-DR8 molecule. In a homology analysis of the amino acid sequences of the six GTF peptides, two binding motifs were found in L/Y--Y/L-A/N and Y/L--N/G/E--Y-V/L/P. Moreover, a new binding motif in PAc was found in L--Y-A. It is suggested that these binding motifs could be useful in designing a dental caries vaccine in humans.

HLA class II alleles and salivary numbers of mutans streptococci and lactobacilli among young adults in Japan

To investigate the genetic predisposition toward the accumulation of oral microorganisms, the association between the alleles of HLA-DQA1, -DQB1 and -DRB1 and the salivary numbers of mutans streptococci and lactobacilli were examined in 102 young adults in Japan. HLA-DQA1*0102, DQB1*0604, DRB1*0802, and DRB1*1302 were weakly associated with the numbers of lactobacilli in saliva samples (P<0.05). HLA-DQB1*0601 was associated with the salivary numbers of mutans streptococci (P<0.01). Two HLA class II haplotypes, HLA-[DRB1*0802-DQA1*0301-DQB1*0302] and HLA-[DRB1*1302-DQA1*0102-DQB1*0604], were also weakly associated with the salivary numbers of lactobacilli (P<0.05). These observations suggest that HLA class II alleles may be related to the salivary populations of oral microorganisms, such as mutans streptococci and lactobacilli.

Inhibitory effects of MoAbs against a surface protein antigen in real-time adherence in vitro and recolonization in vivo of Streptococcus mutans

A surface protein antigen (PAc) of Streptococcus mutans, particularly the A-region of the molecule, has been reported to interact with salivary components on the tooth surface. It might be a candidate antigen inducing the production of antibodies against the adherence of S. mutans to the tooth surface. We investigated the effects of monoclonal antibodies (MoAbs) obtained by immunization of synthetic PAc peptides that completely correspond to the amino acid sequence of part of the A-region. These MoAbs recognize several core B-cell epitopes in the sequence. Two (KH5 and SH2) of these antibodies reacted with both S. mutans and Streptococcus sobrinus, but not with Streptococcus sanguis, Streptococcus salivarius, Porphyromonas gingivalis or Lactobacillus casei. They clearly inhibited the real-time adherence of S. mutans to salivary components in a biosensor. KH5, which showed a real-time inhibition (71%), also significantly prevented the recolonization of S. mutans on the tooth surface in rats. These results suggested that the core B-cell epitope (-Y---L--Y----) recognized by KH5 was the essential sequence in the antigenic epitopes of PAc protein recognized specifically by the inhibitory antibody. Therefore, the amino acid residues were found to be important in the initial attachment of S. mutans to the tooth surface. These results provide for the mechanism of PAc molecule in the initial attachment of S. mutans on the tooth surface and more effective designs for the removal of S. mutans and S. sobrinus from the oral cavity.

Cloning and DNA sequencing of the surface protein antigen I/II (PAa) of Streptococcus cricetus

We have cloned and sequenced the gene encoding the surface protein antigen PAa (antigen I/II family) from Streptococcus cricetus E49 (serotype a) using degenerate PCR. The deduced amino acid sequence of PAa reveals two repeating regions (A region; alanine-rich region, P region; proline-rich region). Two additional tandem repeats were found in the A region and part of the P region was deleted compared to antigen I/II. Homology and phylogenetic analyses reveal that PAa is homologous to Streptococcus sobrinus PAg rather than Streptococcus mutans PAc. Using degenerate PCR a gene homologous to PAc was identified in Streptococcus intermedius, but not found in Streptococcus rattus or Streptococcus anginosus.