Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology , Karl-von-Frisch Strasse 10, 35043 Marburg, Germany.
Biochemistry. 2014 Apr 1;53(12):1899-907. doi: 10.1021/bi500141f. Epub 2014 Mar 21.
Bacteria are polarized with many proteins localizing dynamically to specific subcellular sites. Two GTPase families have important functions in the regulation of bacterial cell polarity, FlhF homologues and small GTPases of the Ras superfamily. The latter consist of only a G domain and are widespread in bacteria. The rod-shaped Myxococcus xanthus cells have two motility systems, one for gliding and one that depends on type IV pili. The function of both systems hinges on proteins that localize asymmetrically to the cell poles. During cellular reversals, these asymmetrically localized proteins are released from their respective poles and then bind to the opposite pole, resulting in an inversion of cell polarity. Here, we review genetic, cell biological, and biochemical analyses that identified two modules containing small Ras-like GTPases that regulate the dynamic polarity of motility proteins. The GTPase SofG interacts directly with the bactofilin cytoskeletal protein BacP to ensure polar localization of type IV pili proteins. In the second module, the small GTPase MglA, its cognate GTPase activating protein (GAP) MglB, and the response regulator RomR localize asymmetrically to the poles and sort dynamically localized motility proteins to the poles. During reversals, MglA, MglB, and RomR switch poles, in that way inducing the relocation of dynamically localized motility proteins. Structural analyses have demonstrated that MglB has a Roadblock/LC7 fold, the central β2 strand in MglA undergoes an unusual screw-type movement upon GTP binding, MglA contains an intrinsic Arg finger required for GTP hydrolysis, and MglA and MglB form an unusual G protein/GAP complex with a 1:2 stoichiometry.
细菌具有极性，许多蛋白质动态定位于特定的亚细胞部位。两个 GTPase 家族在细菌细胞极性的调节中具有重要功能，即 FlhF 同源物和 Ras 超家族的小 GTPases。后者仅由一个 G 结构域组成，在细菌中广泛存在。杆状粘细菌 Xanthus 细胞有两种运动系统，一种用于滑行，另一种依赖于 IV 型菌毛。这两个系统的功能都取决于不对称地定位于细胞两极的蛋白质。在细胞反转过程中，这些不对称定位的蛋白质从各自的极释放出来，然后结合到相反的极，导致细胞极性的反转。在这里，我们综述了遗传、细胞生物学和生化分析，这些分析确定了两个包含小 Ras 样 GTPase 的模块，这些模块调节运动蛋白的动态极性。GTPase SofG 与细菌丝状蛋白 BacP 直接相互作用，以确保 IV 型菌毛蛋白的极性定位。在第二个模块中，小 GTPase MglA、其同源 GTP 酶激活蛋白（GAP）MglB 和应答调节因子 RomR 不对称地定位于两极，并将动态定位的运动蛋白分拣到两极。在反转过程中，MglA、MglB 和 RomR 切换两极，从而诱导动态定位的运动蛋白重新定位。结构分析表明，MglB 具有 Roadblock/LC7 折叠，MglA 中的中央 β2 链在 GTP 结合时经历不寻常的螺旋式运动，MglA 含有一个内在的 Arg 指，用于 GTP 水解，MglA 和 MglB 形成一个不寻常的 G 蛋白/GAP 复合物，具有 1:2 的化学计量比。
