Kawai Yoshikazu, Daniel Richard A, Errington Jeffery
Institute for Cell and Molecular Biosciences, Newcastle University, Medical School, Framlington Place, Newcastle Upon Tyne NE24HH, UK.
Mol Microbiol. 2009 Mar;71(5):1131-44. doi: 10.1111/j.1365-2958.2009.06601.x. Epub 2009 Jan 29.
The bacterial actin homologue MreB plays a key role in cell morphogenesis. In Bacillus subtilis MreB is essential under normal growth conditions and mreB mutants are defective in the control of cell diameter. However, the precise role of MreB is still unclear. Analysis of the lethal phenotypic consequences of mreB disruption revealed an unusual bulging phenotype that precedes cell death. A similar phenotype was seen in wild-type cells at very low Mg(2+) concentrations. We found that inactivation of the major bi-functional penicillin-binding protein (PBP) PBP1 of B. subtilis restored the viability of an mreB null mutant as well as preventing bulging in both mutant and wild-type backgrounds. Bulging was associated with delocalization of PBP1. We show that the normal pattern of localization of PBP1 is dependent on MreB and that the proteins can physically interact using in vivo pull-down and bacterial two-hybrid approaches. Interactions between MreB and several other PBPs were also detected. Our results suggest that MreB filaments associate directly with the peptidoglycan biosynthetic machinery in B. subtilis as part of the mechanism that brings about controlled cell elongation.
细菌肌动蛋白同源物MreB在细胞形态发生中起关键作用。在枯草芽孢杆菌中，MreB在正常生长条件下是必需的，mreB突变体在细胞直径控制方面存在缺陷。然而，MreB的确切作用仍不清楚。对mreB破坏的致死表型后果分析揭示了一种在细胞死亡之前出现的异常凸起表型。在极低镁离子浓度下，野生型细胞中也观察到类似的表型。我们发现枯草芽孢杆菌主要的双功能青霉素结合蛋白（PBP）PBP1的失活恢复了mreB缺失突变体的活力，并防止了突变体和野生型背景下的细胞凸起。细胞凸起与PBP1的定位改变有关。我们表明，PBP1的正常定位模式依赖于MreB，并且使用体内下拉和细菌双杂交方法可以证明这两种蛋白能够发生物理相互作用。还检测到MreB与其他几种PBP之间的相互作用。我们的结果表明，MreB丝直接与枯草芽孢杆菌中的肽聚糖生物合成机制相关联，这是实现受控细胞伸长机制的一部分。
