Structure of Pneumococcal Peptidoglycan Hydrolase LytB Reveals Insights into the Bacterial Cell Wall Remodeling and Pathogenesis
Structure of Pneumococcal Peptidoglycan Hydrolase LytB Reveals Insights into the Bacterial Cell Wall Remodeling and Pathogenesis
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肺炎球菌肽聚糖水解酶 LytB 的结构揭示了细菌细胞壁重塑和发病机制
DOI：
10.1074/jbc.m114.579714
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发表时间：
2014-08-22
影响因子：
4.8
通讯作者：
Zhou, Cong-Zhao
中科院分区：
文献类型：
--
作者：
Bai, Xiao-Hui;Chen, Hui-Jie;Zhou, Cong-Zhao
背景：肺炎球菌内切-N-乙酰氨基葡萄糖苷酶LytB是细胞分裂和定植所必需的。结果：结构分析表明，LytB的催化结构域由三个结构不同的模块组成。结论：LytB的所有三个模块都是其对肽聚糖水解的最佳活性和肺炎球菌粘附到呼吸道上皮细胞所必需的。意义：提供了对LytB介导的肺炎球菌细胞壁重塑和发病机制的结构见解。肺炎链球菌在人类中引起一系列毁灭性的感染。以前的研究表明，内切-N-乙酰氨基葡萄糖苷酶LytB是肺炎球菌细胞分裂和鼻腔定植的关键，但LytB作用的生化机制仍然未知。在这里，我们报告的1.65晶体结构的催化结构域（残基Lys-375-Asp-658）的LytB（称为LytB（CAT）），不包括胆碱结合结构域。LytB（CAT）由三个结构独立的模块组成：SH 3b，WW和GH 73。这些模块形成T形口袋，容纳肽聚糖的推定的四肽-五肽底物。结构比较和模拟表明，GH 73模块的LytB窝藏的活性位点，包括催化残基Glu-564。在体外测定的水解活性表明，LytB喜欢的肽聚糖从lytB缺陷的肺炎球菌，表明存在一个特定的底物LytB在未成熟的肽聚糖。结合体外细胞分散和体内细胞分离试验，我们证明了所有三个模块都是LytB最佳活性所必需的。进一步的功能分析表明，LytB的完全催化活性是肺炎球菌粘附和侵入人肺上皮细胞所必需的。基于结构的比对表明，LytB的独特的模块化组织是高度保守的直向同源物从缓症链球菌组和Gemella物种。这些发现为肺炎球菌细胞壁重塑提供了结构上的见解，并为合理设计抗肺炎球菌生长和相关疾病的治疗药物提供了新的线索。
Background: The pneumococcal endo--N-acetylglucosaminidase LytB is required for cell division and colonization. Results: Structural analysis revealed that the catalytic domain of LytB consists of three structurally distinct modules. Conclusion: All three modules of LytB are necessary for its optimal activity toward peptidoglycan hydrolysis and for pneumococcal adhesion to respiratory epithelial cells. Significance: Provided is the structural insight into LytB-mediated pneumococcal cell wall remodeling and pathogenesis. Streptococcus pneumoniae causes a series of devastating infections in humans. Previous studies have shown that the endo--N-acetylglucosaminidase LytB is critical for pneumococcal cell division and nasal colonization, but the biochemical mechanism of LytB action remains unknown. Here we report the 1.65 crystal structure of the catalytic domain (residues Lys-375-Asp-658) of LytB (termed LytB(CAT)), excluding the choline binding domain. LytB(CAT) consists of three structurally independent modules: SH3b, WW, and GH73. These modules form a T-shaped pocket that accommodates a putative tetrasaccharide-pentapeptide substrate of peptidoglycan. Structural comparison and simulation revealed that the GH73 module of LytB harbors the active site, including the catalytic residue Glu-564. In vitro assays of hydrolytic activity indicated that LytB prefers the peptidoglycan from the lytB-deficient pneumococci, suggesting the existence of a specific substrate of LytB in the immature peptidoglycan. Combined with in vitro cell-dispersing and in vivo cell separation assays, we demonstrated that all three modules are necessary for the optimal activity of LytB. Further functional analysis showed that the full catalytic activity of LytB is required for pneumococcal adhesion to and invasion into human lung epithelial cells. Structure-based alignment indicated that the unique modular organization of LytB is highly conserved in its orthologs from Streptococcus mitis group and Gemella species. These findings provided structural insights into the pneumococcal cell wall remodeling and novel hints for the rational design of therapeutic agents against pneumococcal growth and thereby the related diseases.