Proteases of Streptococcus mutans

Streptococcus mutans is known to produce proteases but their potential as virulence factors that contribute to survival in plaque and tissue breakdown is not understood. Objective: To use genome sequence data to identify putative proteases in S. mutans that may affect the anchorage of known surface proteins or processing of extracellular enzymes. Methods: The S. mutans UA159 genome was searched for genes homologous to known protease genes in other bacteria. Putative protease genes prtC (homologous to a hypothetical P. gingivalis collagenase) and prtM (homologous to a maturation protease in other Gram positive cocci) were identified. The prtC and prtM genes in S. mutans UA159 were targeted for inactivation using insertional mutagenesis and gene replacement mutagenesis respectively. Corresponding mutants were generated in S. mutans strains 3209 and a fresh isolate with strong gelatinase activity. Gene inactivation was confirmed by PCR. The consequence of protease gene knockout on the protein profile of mutants was then studied by SDS-PAGE and Western Blot to examine the effect on release and processing of extracellular enzymes glucosyltransferase, fructosyltransferase and dextranase and surface protein antigens WapA, SpaP and WapE. Gelatinase assays using SDS-PAGE zymograms and gelatin-agar plates were also used to examine the ability of all mutants to hydrolyse gelatin compared to its wildtype strain. Results: No effect on the protein profile of either the prtC or prtM mutant was seen compared to wildtype UA159. No effect on the processing of extracellular enzymes or wall-associated was observed and no effect was seen on gelatinase activity of the mutants compared to wildtype. Conclusion: The prtC and prtM genes of S. mutans are not involved in processing of the major known surface enzymes and protein antigens.