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首页> 外文期刊>Journal of bacteriology >Overproduction of Inactive Variants of the Murein Synthase PBP1B Causes Lysis in Escherichia coli
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Overproduction of Inactive Variants of the Murein Synthase PBP1B Causes Lysis in Escherichia coli

机译：Murein合酶PBP1B的非活性变体的过量生产导致大肠杆菌中的裂解。

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摘要

Penicillin-binding protein 1B (PBP1B) of Escherichia coli is a bifunctional murein synthase containing both a transpeptidase domain and a transglycosylase domain. The protein is present in three forms (α, β, and γ) which differ in the length of their N-terminal cytoplasmic region. Expression plasmids allowing the production of native PBP1B or of PBP1B variants with an inactive transpeptidase or transglycosylase domain or both were constructed. The inactive domains contained a single amino acid exchange in an essential active-site residue. Overproduction of the inactive PBP1B variants, but not of the active proteins, caused lysis of wild-type cells. The cells became tolerant to lysis by inactive PBP1B at a pH of 5.0, which is similar to the known tolerance for penicillin-induced lysis under acid pH conditions. Lysis was also reduced in mutant strains lacking several murein hydrolases. In particular, a strain devoid of activity of all known lytic transglycosylases was virtually tolerant, indicating that mainly the lytic transglycosylases are responsible for the observed lysis effect. A possible structural interaction between PBP1B and murein hydrolases in vivo by the formation of a multienzyme complex is discussed.
机译：大肠埃希菌的青霉素结合蛋白1B（PBP1B）是一种双功能的Murein合酶，同时含有一个转肽酶结构域和一个转糖基酶结构域。该蛋白质以三种形式（α，β和γ）存在，其N末端胞质区的长度不同。构建表达质粒，其允许产生天然PBP1B或具有失活的转肽酶或转糖基化酶结构域或两者的PBP1B变体。非活性结构域在必需的活性位点残基中包含单个氨基酸交换。非活性PBP1B变体的过度生产，而不是活性蛋白的过度生产，导致野生型细胞裂解。在pH为5.0时，细胞对非活性PBP1B的裂解耐受，这与在酸性pH条件下青霉素诱导的裂解的已知耐受性相似。在缺乏几种murein水解酶的突变菌株中，裂解也减少了。特别地，没有所有已知的裂解转糖基酶活性的菌株实际上是耐受的，表明主要是裂解转糖基酶引起观察到的裂解作用。讨论了通过形成多酶复合物在体内PBP1B和murein水解酶之间可能的结构相互作用。

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