Kawai Yoshikazu, Asai Kei, Errington Jeffery
Institute for Cell and Molecular Biosciences, Newcastle University, Medical School, Newcastle Upon Tyne NE2 4HH, UK.
Mol Microbiol. 2009 Aug;73(4):719-31. doi: 10.1111/j.1365-2958.2009.06805.x. Epub 2009 Jul 29.
MreB proteins are bacterial actin homologues thought to have a role in cell shape determination by positioning the cell wall synthetic machinery. Many bacteria, particularly Gram-positives, have more than one MreB isoform. Bacillus subtilis has three, MreB, Mbl and MreBH, which colocalize in a single helical structure. We now show that the helical pattern of peptidoglycan (PG) synthesis in the cylindrical part of the rod-shaped cell is governed by the redundant action of the three MreB isoforms. Single mutants for any one of mreB isoforms can still incorporate PG in a helical pattern and generate a rod shape. However, after depletion of MreB in an mbl mutant (or depletion of all three isoforms) lateral wall PG synthesis was impaired and the cells became spherical and lytic. Overexpression of any one of the MreB isoforms overcame the lethality as well as the defects in lateral PG synthesis and cell shape. Furthermore, MreB and Mbl can associate with the peptidoglycan biosynthetic machinery independently. However, no single MreB isoform was able to support normal growth under various stress conditions, suggesting that the multiple isoforms are used to allow cells to maintain proper growth and morphogenesis under changing and sometimes adverse conditions.
MreB蛋白是细菌肌动蛋白的同源物，被认为通过定位细胞壁合成机制在细胞形状决定中发挥作用。许多细菌，特别是革兰氏阳性菌，具有不止一种MreB异构体。枯草芽孢杆菌有三种，即MreB、Mbl和MreBH，它们共定位于单一的螺旋结构中。我们现在表明，杆状细胞圆柱形部分的肽聚糖（PG）合成螺旋模式受三种MreB异构体的冗余作用控制。任何一种MreB异构体的单突变体仍能以螺旋模式掺入PG并产生杆状形状。然而，在mbl突变体中耗尽MreB后（或耗尽所有三种异构体），侧壁PG合成受损，细胞变成球形并裂解。任何一种MreB异构体的过表达都克服了致死性以及侧壁PG合成和细胞形状的缺陷。此外，MreB和Mbl可以独立地与肽聚糖生物合成机制结合。然而，没有单一的MreB异构体能够在各种应激条件下支持正常生长，这表明多种异构体用于使细胞在不断变化且有时不利的条件下维持适当的生长和形态发生。
