Nearly all bacteria are encased in a peptidoglycan cell wall, an essential crosslinked matrix of polysaccharide strands and short peptide stems. In the Gram-negative model organism Escherichia coli, more than forty cell wall synthases and autolysins coordinate the growth and division of the peptidoglycan sacculus in the periplasm. The precise contribution of many of these enzymes to cell wall metabolism remains unclear due to significant apparent redundancy, particularly among the cell wall autolysins. E. coli produces three major LytC-type-N-acetylmuramoyl-L-alanine amidases, which share a role in separating the newly formed daughter cells during cytokinesis. Here, we reveal two of the three amidases exhibit growth medium-dependent changes in activity. Specifically, we report acidic growth conditions stimulate AmiB—and to a lesser extent, AmiC—activity. Combining computational and genetic analysis, we demonstrate that low pH-dependent stimulation of AmiB requires three periplasmic amidase activators: EnvC, NlpD, and YgeR. Altogether, our findings support overlapping, but not redundant, roles for the E. coli amidases in cell separation and illuminate the physiochemical environment as an important mediator of cell wall enzyme activity.

中文翻译：

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大肠杆菌肽聚糖酰胺酶的活性库随理化环境而变化

几乎所有细菌都包裹在肽聚糖细胞壁中，后者是多糖链和短肽茎的必不可少的交联基质。在革兰氏阴性模型生物大肠杆菌中，超过四十种细胞壁合酶和自溶素协调周质中肽聚糖囊的生长和分裂。由于明显的冗余，尤其是在细胞壁自溶素中，许多这些酶对细胞壁代谢的精确贡献仍不清楚。大肠杆菌产生三种主要的LytC型-N-乙酰基村酰基-L-丙氨酸酰胺酶，在胞质分裂过程中，它们在分离新形成的子细胞中具有共同的作用。在这里，我们揭示了三种酰胺酶中的两种表现出生长介质依赖性的活性变化。具体来说，我们报道了酸性生长条件会刺激AmiB（在较小程度上会刺激AmiC）的活性。结合计算和遗传分析，我们证明AmiB的低pH依赖性刺激需要三种周质酰胺酶激活剂：EnvC，NlpD和YgeR。总的来说，我们的发现支持大肠杆菌酰胺酶在细胞分离中的作用是重叠但不是多余的，并阐明了作为细胞壁酶活性的重要介质的理化环境。