Geissler Brett, Shiomi Daisuke, Margolin William
Department of Microbiology and Molecular Genetics, University of Texas Medical School, 6431 Fannin Street, Houston, TX 77030, USA.
Microbiology (Reading). 2007 Mar;153(Pt 3):814-825. doi: 10.1099/mic.0.2006/001834-0.
Formation of the FtsZ ring (Z ring) in Escherichia coli is the first step in the assembly of the divisome, a protein machine required for cell division. Although the biochemical functions of most divisome proteins are unknown, several, including ZipA, FtsA and FtsK, have overlapping roles in ensuring that the Z ring assembles at the cytoplasmic membrane, and that it is active. As shown previously, a single amino acid change in FtsA, R286W, also called FtsA*, bypasses the requirement for either ZipA or FtsK in cell division. In this study, the properties of FtsA* were investigated further, with the eventual goal of understanding the molecular mechanism behind the bypass. Compared to wild-type FtsA, the presence of FtsA* resulted in a modest but significant decrease in the mean length of cells in the population, accelerated the reassembly of Z rings, and suppressed the cell-division block caused by excessively high levels of FtsZ. These effects were not mediated by Z-ring remodelling, because FtsA* did not alter the kinetics of FtsZ turnover within the Z ring, as measured by fluorescence recovery after photobleaching. FtsA* was also unable to permit normal cell division at below normal levels of FtsZ, or after thermoinactivation of ftsZ84(ts). However, turnover of FtsA* in the ring was somewhat faster than that of wild-type FtsA, and overexpressed FtsA* did not inhibit cell division as efficiently as wild-type FtsA. Finally, FtsA* interacted more strongly with FtsZ compared with FtsA in a yeast two-hybrid system. These results suggest that FtsA* interacts with FtsZ in a markedly different way compared with FtsA.
在大肠杆菌中形成FtsZ环（Z环）是细胞分裂体组装的第一步，细胞分裂体是细胞分裂所需的一种蛋白质机器。尽管大多数细胞分裂体蛋白的生化功能尚不清楚，但包括ZipA、FtsA和FtsK在内的几种蛋白在确保Z环在细胞质膜上组装并保持活性方面具有重叠作用。如先前所示，FtsA中的单个氨基酸变化R286W（也称为FtsA*）可绕过细胞分裂中对ZipA或FtsK的需求。在本研究中，进一步研究了FtsA的特性，最终目标是了解这种绕过背后的分子机制。与野生型FtsA相比，FtsA的存在导致群体中细胞的平均长度适度但显著缩短，加速了Z环的重新组装，并抑制了由过高水平的FtsZ引起的细胞分裂阻滞。这些效应不是由Z环重塑介导的，因为通过光漂白后的荧光恢复测量，FtsA并没有改变Z环内FtsZ周转的动力学。FtsA也无法在低于正常水平的FtsZ时或ftsZ84(ts)热失活后允许正常细胞分裂。然而，FtsA在环中的周转比野生型FtsA略快，并且过表达的FtsA抑制细胞分裂的效率不如野生型FtsA。最后，在酵母双杂交系统中，与FtsA相比，FtsA与FtsZ的相互作用更强。这些结果表明，与FtsA相比，FtsA与FtsZ的相互作用方式明显不同。
