PDF(Pubmed)
Abstract：
The bacterial cell wall is composed primarily of peptidoglycan (PG), a poly-aminosugar that is essential to sustain cell shape, growth, and structural integrity. PG is synthesized by class A/B penicillin-binding proteins (a/bPBPs) and shape, elongation, division, and sporulation (SEDS) proteins like RodA (as part of the Rod system cell elongation machinery) and degraded by \"autolytic\" enzymes to accommodate growth processes. It is thought that autolysins (particularly endopeptidases [EPs]) are required for PG synthesis and incorporation by creating gaps that are patched and paved by PG synthases, but the exact relationship between autolysins and PG synthesis remains incompletely understood. Here, we have probed the consequences of EP depletion for PG synthesis in the diarrheal pathogen Vibrio cholerae We found that EP depletion resulted in severe morphological and division defects, but these cells continued to increase in mass and aberrantly incorporated new cell wall material. Mass increase proceeded in the presence of Rod system inhibitors, but cells lysed upon inhibition of aPBPs, suggesting that aPBPs are required for structural integrity under these conditions. The Rod system, although not essential for the observed mass increase, remained functional even after prolonged EP depletion. Last, heterologous expression of an EP from Neisseria gonorrhoeae fully complemented growth and morphology of an EP-insufficient V. cholerae, highlighting the possibility that the PG synthases may not necessarily function via direct interaction with EPs. Overall, our findings suggest that during EP insufficiency in V. cholerae, aPBPs become essential for structural integrity while the Rod system is unable to promote proper cell expansion.IMPORTANCE Synthesis and turnover of the bacterial cell wall must be tightly coordinated to avoid structural integrity failure and cell death. Details of this coordination are poorly understood, particularly if and how cell wall turnover enzymes are required for the activity of the different cell wall synthesis machines, the aPBPs and the Rod system. Our results suggest that in Vibrio cholerae, one class of turnover enzymes, the endopeptidases, are necessary for proper cell elongation and division. aPBPs become essential for maintaining structural integrity during EP insufficiency, while the Rod system remains active but contributes little to cell expansion under these conditions. Our results suggest that aPBPs are more versatile than the Rod system in their ability to recognize cell wall gaps formed by autolysins other than the major endopeptidases, adding to our understanding of the coordination between autolysins and cell wall synthases. A detailed understanding of autolysin biology may promote the development of antibiotics that target these essential turnover processes.
摘要：
细菌细胞壁主要由肽聚糖（PG）组成，一种对维持细胞形状至关重要的多氨基糖，增长,和结构完整性。PG由A/B类青霉素结合蛋白（a/bPBP）和形状合成，伸长率,司,和孢子形成（SEDS）蛋白质，如RodA（作为棒系统细胞伸长机制的一部分），并通过“自溶”酶降解以适应生长过程。认为自溶素（特别是内肽酶[EP]）是PG合成和掺入所必需的，通过产生由PG合酶修补和铺垫的缺口，但是自溶素与PG合成之间的确切关系仍未完全了解。这里,我们探讨了腹泻病原体霍乱弧菌中EP耗竭对PG合成的影响。我们发现EP耗竭导致严重的形态和分裂缺陷，但是这些细胞的质量继续增加，并且异常地掺入了新的细胞壁材料。在棒系统抑制剂的存在下进行质量增加，但是细胞在抑制aPBPs时裂解，这表明在这些条件下，aPBP是结构完整性所必需的。杆系统,虽然不是观察到的质量增加所必需的，即使在延长EP耗尽后仍保持功能。最后,淋病奈瑟菌EP的异源表达完全补充了EP不足的霍乱弧菌的生长和形态，强调PG合酶不一定通过与EP的直接相互作用起作用的可能性。总的来说,我们的研究结果表明，在霍乱弧菌的EP功能不全期间，PBP成为必要的结构完整性而杆系统是无法促进适当的细胞扩大。重要性细菌细胞壁的合成和周转必须紧密协调以避免结构完整性破坏和细胞死亡。这种协调的细节知之甚少，特别是不同细胞壁合成机器的活性是否以及如何需要细胞壁周转酶，APBPs和杆系统。我们的结果表明，在霍乱弧菌中，一类周转酶，内肽酶，是正确的细胞伸长和分裂所必需的。在EP不足期间，PBP成为维持结构完整性所必需的，虽然棒系统保持活性，但在这些条件下对细胞扩增贡献很小。我们的结果表明，aPBP比Rod系统更通用，能够识别由自溶素形成的细胞壁间隙，而不是主要的内肽酶。增加了我们对自溶素和细胞壁合酶之间协调的理解。对自溶素生物学的详细了解可能会促进针对这些基本周转过程的抗生素的开发。
