Schirner Kathrin, Errington Jeff
Institute for Cell and Molecular Biosciences, Newcastle University, Medical School, Framlington Place, Newcastle Upon Tyne NE2 4HH, UK.
Microbiology (Reading). 2009 Nov;155(Pt 11):3611-3621. doi: 10.1099/mic.0.030692-0. Epub 2009 Jul 30.
The prokaryotic cytoskeletal protein MreB is thought to govern cell shape by positioning the cell wall synthetic apparatus at growth sites in the cell. In rod-shaped bacteria it forms helical filaments that run around the periphery of the rod during elongation. Gram-positive bacteria often contain more than one mreB gene. Bacillus subtilis has three mreB-like genes, mreB, mbl and mreBH, the first two of which have been shown to be essential under normal growth conditions. Expression of an mreB homologue from the closely related organism Bacillus licheniformis did not have any effect on cell growth or morphology. In contrast, expression of mreB from the phylogenetically more distant bacterium Clostridium perfringens produced shape defects and ultimately cell death, due to disruption of the endogenous MreB cytoskeleton. However, expression of either mreB(B. licheniformis) (mreB(Bl)) or mreB(C. perfringens) (mreB(Cp)) was sufficient to confer a rod shape to B. subtilis deleted for the three mreB isologues, supporting the idea that the three proteins have largely redundant functions in cell morphogenesis. Expression of mreBCD(Bl) could fully compensate for the loss of mreBCD in B. subtilis and led to the formation of rod-shaped cells. In contrast, expression of mreBCD(Cp) was not sufficient to confer a rod shape to B. subtilis Delta mreBCD, indicating that a complex of these three cell shape determinants is not enough for cell morphogenesis of B. subtilis.
原核细胞骨架蛋白MreB被认为通过将细胞壁合成装置定位在细胞的生长位点来控制细胞形状。在杆状细菌中，它形成螺旋状细丝，在伸长过程中围绕杆的外周运行。革兰氏阳性细菌通常含有不止一个mreB基因。枯草芽孢杆菌有三个mreB样基因，即mreB、mbl和mreBH，其中前两个已被证明在正常生长条件下是必需的。来自密切相关的地衣芽孢杆菌的mreB同源物的表达对细胞生长或形态没有任何影响。相比之下，来自系统发育上更远的产气荚膜梭菌的mreB的表达由于内源性MreB细胞骨架的破坏而导致形状缺陷并最终导致细胞死亡。然而，mreB（地衣芽孢杆菌）（mreB（Bl））或mreB（产气荚膜梭菌）（mreB（Cp））的表达足以使缺失三个mreB异构体的枯草芽孢杆菌呈现杆状，这支持了这三种蛋白质在细胞形态发生中具有很大程度冗余功能的观点。mreBCD（Bl）的表达可以完全补偿枯草芽孢杆菌中mreBCD的缺失并导致杆状细胞的形成。相比之下，mreBCD（Cp）的表达不足以使枯草芽孢杆菌ΔmreBCD呈现杆状，这表明这三个细胞形状决定因素的复合物不足以实现枯草芽孢杆菌的细胞形态发生。
