The Redundancy of Peptidoglycan Carboxypeptidases Ensures Robust Cell Shape Maintenance in Escherichia coli.
The Redundancy of Peptidoglycan Carboxypeptidases Ensures Robust Cell Shape Maintenance in Escherichia coli.
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DOI：
10.1128/mbio.00819-16
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发表时间：
2016-06-21
期刊：
影响因子：
6.4
通讯作者：
Vollmer W
中科院分区：
文献类型：
--
作者：
Peters K;Kannan S;Rao VA;Biboy J;Vollmer D;Erickson SW;Lewis RJ;Young KD;Vollmer W
肽聚糖（PG）是细菌细胞壁的重要结构成分，通过在细胞质膜周围形成连续层来维持细胞的完整性和形状。大肠杆菌的薄PG层存在于周质中，周质是一个独特的隔室，其组成和pH值可以根据细胞的局部环境而变化。因此，PG层的生长必须足够稳健以允许细胞在不同条件下生长和分裂。我们分析了28个突变体缺乏多种PG酶（青霉素结合蛋白[PBPs]）生长后，在酸性或近中性pH介质的PG组合物。DD-羧肽酶的胞肽谱的统计分析特别地，当细胞在酸性pH下生长时，DD-CP酶PBP 6 b的不存在引起PG的五肽含量的显著增加以及形态缺陷。（PBP 4、PBP 4 b、PBP 5、PBP 6a、PBP 7和AmpH）和PG合酶PBP 1B在酸性pH下对五肽修剪活性的贡献较小或为零。我们解决了PBP 6 b的晶体结构，并且还证明了该酶在酸性pH下更稳定并且具有较低的Km，因此，PBP 6 b是一种有助于在低pH下维持细胞形状的专门DD-CP酶，并且大肠杆菌似乎在不同条件下利用多余的DD-CP酶进行正常生长。大肠杆菌需要肽聚糖DD-羧肽酶通过控制肽聚糖合成转肽酶可用的五肽底物的量来维持细胞形状。为什么大肠杆菌有八个，似乎多余的dd-carboxypeptidases仍然是未知的。我们现在表明，其中一种dd-羧肽酶（PBP 6 b）对于酸性生长培养基中的细胞形状维持很重要，这与该酶在低pH值下具有更高的活性和稳定性一致。因此，多种具有不同酶性质的dd-羧肽酶的存在可能允许大肠杆菌在各种生长条件下维持正常的细胞形状。
Peptidoglycan (PG) is an essential structural component of the bacterial cell wall and maintains the integrity and shape of the cell by forming a continuous layer around the cytoplasmic membrane. The thin PG layer of Escherichia coli resides in the periplasm, a unique compartment whose composition and pH can vary depending on the local environment of the cell. Hence, the growth of the PG layer must be sufficiently robust to allow cell growth and division under different conditions. We have analyzed the PG composition of 28 mutants lacking multiple PG enzymes (penicillin-binding proteins [PBPs]) after growth in acidic or near-neutral-pH media. Statistical analysis of the muropeptide profiles identified dd-carboxypeptidases (DD-CPases) that were more active in cells grown at acidic pH. In particular, the absence of the DD-CPase PBP6b caused a significant increase in the pentapeptide content of PG as well as morphological defects when the cells were grown at acidic pH. Other DD-CPases (PBP4, PBP4b, PBP5, PBP6a, PBP7, and AmpH) and the PG synthase PBP1B made a smaller or null contribution to the pentapeptide-trimming activity at acidic pH. We solved the crystal structure of PBP6b and also demonstrated that the enzyme is more stable and has a lower Km at acidic pH, explaining why PBP6b is more active at low pH. Hence, PBP6b is a specialized DD-CPase that contributes to cell shape maintenance at low pH, and E. coli appears to utilize redundant DD-CPases for normal growth under different conditions. Escherichia coli requires peptidoglycan dd-carboxypeptidases to maintain cell shape by controlling the amount of pentapeptide substrates available to the peptidoglycan synthetic transpeptidases. Why E. coli has eight, seemingly redundant dd-carboxypeptidases has remained unknown. We now show that one of these dd-carboxypeptidases, PBP6b, is important for cell shape maintenance in acidic growth medium, consistent with the higher activity and stability of the enzyme at low pH. Hence, the presence of multiple dd-carboxypeptidases with different enzymatic properties may allow E. coli to maintain a normal cell shape under various growth conditions.