Deletion in sortase gene of Streptococcus mutans Ingbritt

Our previous studies on Streptococcus mutans have demonstrated that surface proteins containing a C-terminal sorting signal, such as surface protein antigen (PAc), glucan-binding protein C (GbpC) and dextranase (Dex), are anchored to the cell wall by a sortase (SrtA). In this study we found that, unlike other strains of S. mutans, strain Ingbritt did not exhibit cell wall-anchoring of PAc, GbpC and Dex. It is speculated that the SrtA of strain Ingbritt did not function in the cell wall-anchoring process of these surface proteins. Sequence analysis revealed a deletion of an 11-bp nucleotide sequence in the srtA gene of strain Ingbritt, resulting in the generation of a new termination codon, resulting in production of an incomplete SrtA enzyme protein. As a result, strain Ingbritt showed a localization change of PAc, GbpC and Dex in the cell, implying that strain Ingbritt loses the biological functions mediated by the cell surface-associated proteins of S. mutans. These results suggest that strain Ingbritt could be less cariogenic than other strains of S. mutans.