Alterations in immunodominance of Streptococcus mutans AgI/II: Lessons learned from immunomodulatory antibodies

Abstract

Streptococcus mutans Antigen I/II (AgI/II) has been widely studied as a candidate vaccine antigen against human dental caries. In this report we follow up on prior studies that indicated that anti-AgI/II immunomodulatory monoclonal antibodies (MAbs) exerted their effects by destabilizing the native protein structure and exposing cryptic epitopes. We show here that similar results can be obtained by immunizing mice with truncated polypeptides out of the context of an intra-molecular interaction that occurs within the full-length molecule and that appears to dampen the functional response against at least two important target epitopes. Putative T cell epitopes that influenced antibody specificity were identified immediately upstream of the alanine-rich repeat domain. Adherence inhibiting antibodies could be induced against two discrete domains of the protein, one corresponding to the central portion of the molecule and the other corresponding to the C-terminus.

Identification of a Supramolecular Functional Architecture of Streptococcus mutans Adhesin P1 on the Bacterial Cell Surface

“…1C) have provided valuable insights into the antigenic regions of the protein as well as into the mechanism of protection observed with anti-P1 antibodies (49,56,75,90,91). We used single molecule force spectroscopy utilizing several different anti-P1 mAbs (Fig.…”

New small-molecule inhibitors of dihydrofolate reductase inhibit Streptococcus mutans

“…Various strategies aimed at preventing dental caries have been attempted on the basis of various criteria: increasing antimicrobial activity [2]; replacement of sucrose with other sweeteners [3]; inhibition of the key matrix-producing enzymeglucosyltransferases either by vaccine approaches [4] or enzymatic inhibitors [5]; and targeting another important surface protein antigen I/II using immunomodulatory monoclonal antibodies [6]. However, in vivo application of these promising approaches is uncertain.…”

An intramolecular lock facilitates folding and stabilizes the tertiary structure of Streptococcus mutans adhesin P1

“…Our crystal structure lends insight into why the N-terminal segment of P1 has such a pronounced impact on its immunogenicity, antigenicity, folding, stability, and adherent function (17,(21)(22)(23)(24)(25)(26), The NA1/ P3C complex contains an elongated alpha/polyproline type II hybrid helix similar to that identified in the crystallized A3VP1 fragment (14), except that in this case it comprises the A1 and P3 repeats rather than the A3 and P1 repeats. In addition, the pre-A region N terminus is found in immediate juxtaposition with the post-P region sequence and extends into the globular C-terminal domains.…”

“…Thus, perturbing stability would allow the formation of protective antibodies against epitopes that would not otherwise be immunogenic in the locked structure. In more recent experiments, immunization of mice with P3C alone elicited antibodies capable of inhibiting adherence of S. mutans to immobilized human salivary agglutinin; however, immunization with the P3C/NA1 complex was significantly less effective (21). Taken together, these previous studies suggest that the association between the N-and C-terminal regions of P1 not only stabilizes the protein structure and enhances the adherent function of the C-terminal region, but also acts to mask protective epitopes from the immune system.…”