The first structure of a pneumococcal autolysin, that of the LytC lysozyme, has been solved in ternary complex with choline and a pneumococcal peptidoglycan (PG) fragment. The active site of the hydrolase module is not fully exposed but is oriented toward the choline-binding module, which accounts for its unique in vivo features in PG hydrolysis, its activation and its regulatory mechanisms. Because of the unusual hook-shaped conformation of the multimodular protein, it is only able to hydrolyze non-cross-linked PG chains, an assertion validated by additional experiments. These results explain the activation of LytC by choline-binding protein D (CbpD) in fratricide, a competence-programmed mechanism of predation of noncompetent sister cells. The results provide the first structural insights to our knowledge into the critical and central function that LytC plays in pneumococcal virulence and explain a long-standing puzzle of how murein hydrolases can be controlled to avoid self-lysis during bacterial growth and division.

中文翻译：

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从模块化杀伤因子 LytC 的晶体结构洞察肺炎球菌自相残杀。

肺炎球菌自溶素的第一个结构，即 LytC 溶菌酶的结构，已在胆碱和肺炎球菌肽聚糖 (PG) 片段的三元复合物中得到解决。水解酶模块的活性位点并未完全暴露，而是面向胆碱结合模块，这说明了其在 PG 水解、激活和调节机制中的独特体内特征。由于多模块蛋白的不寻常的钩形构象，它只能水解非交联的 PG 链，这一说法得到了额外的实验验证。这些结果解释了在自相残杀中胆碱结合蛋白 D (CbpD) 激活 LytC，这是一种捕食无能力姐妹细胞的能力程序化机制。