The autolytic activity of cariogenic bacteria is useful as a target to develop antibacterial drugs.

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The AtlA protein predicted for atlA of Streptococcus mutans Xc is composed of 979 amino acids with a molecular weight of 107,279 and has the conserved b-1,4-N-acetylmuramidase (lysozyme) domain in the C-terminal portion. Sodium dodecyl sulfate extracts of strain Xc showed two major bacteriolytic bands with molecular masses of 107 and 79 kDa, both of which were absent in an atlA-inactivated mutant. Western blot analysis revealed that the 79-kDa band is derived from the 107-kDa peptide by cleavage of its N-terminal portion. The inactivation of atlA resulted in a marked decrease of autolysis and the formation of very long chains of cells as compared with the parent strain. Although both the parent and mutant strains formed biofilms in the presence of sucrose, the biofilms formed by the mutant had a sponge-like architecture with large gaps and contained 30% less biomass than those of the parent strain. Furthermore, strain Xc formed the glucose-dependent, loose biofilms in the absence of sucrose, but the mutant lost this ability. These results suggest that AtlA may play an important role in biofilm formation by S. mutans. Next, we tried to purify the AtlA protein, but unfortunately failed it. The antibody produced against the C-terminal peptide containing the b-1,4-N-acetylmuramidase domain drastically inhibited the autolytic activity and the biofilm formation of strain Xc. This inhibition was specific to S. mutans among oral streptococci. These results indicate that the catalytic domain of AtlA is located at the C-terminus, suggesting that further characterization of this domain may provide a means to control cariogenic dental plaque formation.