Identification of MltG as a potential terminase for peptidoglycan polymerization in bacteria.
Identification of MltG as a potential terminase for peptidoglycan polymerization in bacteria.
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DOI：
10.1111/mmi.13258
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发表时间：
2016-02
影响因子：
3.6
通讯作者：
Bernhardt TG
中科院分区：
文献类型：
--
作者：
Yunck R;Cho H;Bernhardt TG
由肽聚糖（PG）组成的细胞壁加强了细菌细胞的渗透性裂解。被称为青霉素结合蛋白（PBPs）的合成酶是青霉素和相关抗生素的靶标，它聚合PG的聚糖链，并通过附着的肽将其交联到细胞壁网中。被PBPs插入到基质中的聚糖链的平均长度被认为在细菌形态发生中起重要作用，但控制这一过程的聚合终止因子尚未被发现。在这里，我们报告鉴定大肠杆菌MltG （YceG）作为糖聚合的潜在终止酶，在细菌中广泛保守。在PG合成酶PBP1b缺陷的细胞中，通过筛选产生致死表型的多拷贝质粒，最初分离出含有mltG的克隆。生化研究表明，MltG是一种具有内解转糖基酶活性的内膜酶，能够在多糖聚合物的内部位置进行切割。放射性标记实验进一步证实了体内对mltg依赖性的新生PG加工，细菌双杂交分析发现了MltG-PBP1b相互作用。与野生型细胞相比，缺乏MltG的突变体在PG中具有更长的聚糖。因此，我们的综合结果与MltG与PG合成配合物结合以切割新生聚合物并终止其延伸的模型一致。
Bacterial cells are fortified against osmotic lysis by a cell wall made of peptidoglycan (PG). Synthases called penicillin-binding proteins (PBPs), the targets of penicillin and related antibiotics, polymerize the glycan strands of PG and crosslink them into the cell wall meshwork via attached peptides. The average length of glycan chains inserted into the matrix by the PBPs is thought to play an important role in bacterial morphogenesis, but polymerization termination factors controlling this process have yet to be discovered. Here, we report the identification of Escherichia coli MltG (YceG) as a potential terminase for glycan polymerization that is broadly conserved in bacteria. A clone containing mltG was initially isolated in a screen for multicopy plasmids generating a lethal phenotype in cells defective for the PG synthase PBP1b. Biochemical studies revealed that MltG is an inner membrane enzyme with endolytic transglycosylase activity capable of cleaving at internal positions within a glycan polymer. Radiolabeling experiments further demonstrated MltG-dependent nascent PG processing in vivo, and bacterial two-hybrid analysis identified an MltG-PBP1b interaction. Mutants lacking MltG were also shown to have longer glycans in their PG relative to wild-type cells. Our combined results are thus consistent with a model in which MltG associates with PG synthetic complexes to cleave nascent polymers and terminate their elongation.