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

预测的变形链球菌Xc的AtlA蛋白由979个氨基酸组成，分子量为107279，在c端具有保守的b-1,4- n -乙酰酶（溶菌酶）结构域。菌株Xc的十二烷基硫酸钠提取物显示出两条主要的溶菌带，分子量为107和79 kDa，这两条条带在atla灭活突变体中都不存在。Western blot分析显示，79-kDa的条带是由107-kDa肽的n端部分切割而来。与亲本菌株相比，atlA的失活导致细胞自溶明显减少，形成很长的细胞链。虽然在蔗糖存在的情况下，亲本菌株和突变菌株都能形成生物膜，但突变菌株形成的生物膜结构呈海绵状，间隙大，生物量比亲本菌株少30%。此外，菌株Xc在缺乏蔗糖的情况下形成葡萄糖依赖的松散生物膜，但突变体失去了这种能力。这些结果表明，AtlA可能在变形链球菌的生物膜形成中起重要作用。接下来，我们试图纯化AtlA蛋白，但不幸的是没有成功。针对含有b-1,4- n -乙酰酶结构域的c端肽产生的抗体可显著抑制菌株Xc的自溶活性和生物膜的形成。这种抑制作用对口腔链球菌中的变形链球菌具有特异性。这些结果表明，AtlA的催化结构域位于c端，表明进一步表征该结构域可能为控制牙菌斑的形成提供一种手段。

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.