Binding From both sides: TolR and full-length OmpA bind and maintain the local structure of the E. coli cell wall.

We present a molecular modelling and simulation study of the <em>E. coli </em>cell envelope, with a particular focus on the role of TolR, a native protein of the <em>E. coli </em>inner membrane in interactions with the cell wall. TolR has been proposed to bind to peptidoglycan, but the only structure of this protein thus far is in a conformation in which the putative peptidoglycan binding domain is not accessible. We show that a model of the extended conformation of the protein in which this domain is exposed, binds peptidoglycan largely through electrostatic interactions. Non-covalent interactions of TolR and OmpA with the cell wall, from the inner membrane and outer membrane sides respectively, maintain the position of the cell wall even in the absence of Braun’s lipoprotein. The charged residues that mediate the cell-wall interactions of TolR in our simulations, are conserved across a number of species of Gram-negative bacteria.本研究针对大肠杆菌（E. coli）细胞包膜开展分子建模与模拟研究，重点聚焦于TolR的作用——TolR是大肠杆菌内膜的天然蛋白，参与细胞壁的相互作用过程。已有研究推测TolR可结合肽聚糖（peptidoglycan），但目前仅解析出该蛋白的一种构象，其推定的肽聚糖结合结构域处于无法接触配体的状态。本研究表明，当该蛋白处于伸展构象、此结构域暴露时，可主要通过静电相互作用结合肽聚糖。TolR与外膜蛋白A（OmpA）分别从内膜侧与外膜侧与细胞壁形成非共价相互作用，即便在缺失布拉氏脂蛋白（Braun’s lipoprotein）的情况下，仍可维持细胞壁的空间位置。在本模拟实验中介导TolR与细胞壁相互作用的带电残基，在多种革兰氏阴性菌（Gram-negative bacteria）中均具有序列保守性。