Functional and immunogenic characterization of two cloned regions of Streptococcus mutans glucosyltransferase I

Glucosyltransferase (GTF) enzymes of mutans streptococci are considered vir ulence factors due to their ability to synthesize adhesive glucans, which f acilitate cell-to-cell adherence and accumulation, In this study we report the cloning, expression, and characterization of the catalytic (CAT) and gl ucan-binding (GLU) domains of S. mutans GTF-I encoded by gtfB. The CAT and GLU polypeptides represent amino acid residues 253 to 628 and 1183 to 1473, respectively, of S. mutans GTF-I. Antibodies to recombinant CAT and GLU we re generated in rabbits and purified by affinity chromatography, Purified a nti-CAT antibodies significantly inhibited water-insoluble glucan synthesis by S. mutans and S. sobrinus GTFs (P < 0.0001 and P < 0.05, respectively). The purified anti-GLU antibodies significantly inhibited both water-insolu ble and water-soluble glucan synthesis by S. mutans GTFs (P < 0.0001 and P < 0.05, respectively). These results demonstrate that anti-CAT and anti-GLU antibodies are capable of inhibiting a variety of GTF activities. Since an tibodies to S, mutans in saliva are implicated in protection against diseas e,,ve next assessed the ability of CAT and GLU polypeptides to induce mucos al antibody responses in mice. Intranasal (i,n.) immunization of mice with CAT showed significantly (P < 0.005) elevated levels of specific immunoglob ulin G (IgG) antibody activity in serum and specific IgA antibody activity in serum, saliva, vaginal washes, and fecal samples. GLU immunized animals showed significantly (P < 0.005) elevated levels of specific IgA antibody a ctivity in serum and vaginal secretions. Taken together, these results demo nstrate that the recombinant: CAT and GLU polypeptides are effective in ind ucing both mucosal and systemic immune responses. The ability of these poly peptides to induce a mucosal IgA immune response in mice after i.n. immuniz ation supports their use as subunit vaccine candidates in the development o f an anticaries vaccine.