Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
PLoS Genet. 2022 Sep 6;18(9):e1010384. doi: 10.1371/journal.pgen.1010384. eCollection 2022 Sep.
The Ras-like GTPase MglA is a key regulator of front-rear polarity in the rod-shaped Myxococcus xanthus cells. MglA-GTP localizes to the leading cell pole and stimulates assembly of the two machineries for type IV pili-dependent motility and gliding motility. MglA-GTP localization is spatially constrained by its cognate GEF, the RomR/RomX complex, and GAP, the MglB Roadblock-domain protein. Paradoxically, RomR/RomX and MglB localize similarly with low and high concentrations at the leading and lagging poles, respectively. Yet, GEF activity dominates at the leading and GAP activity at the lagging pole by unknown mechanisms. Here, we identify RomY and show that it stimulates MglB GAP activity. The MglB/RomY interaction is low affinity, restricting formation of the bipartite MglB/RomY GAP complex almost exclusively to the lagging pole with the high MglB concentration. Our data support a model wherein RomY, by forming a low-affinity complex with MglB, ensures that the high MglB/RomY GAP activity is confined to the lagging pole where it dominates and outcompetes the GEF activity of the RomR/RomX complex. Thereby, MglA-GTP localization is constrained to the leading pole establishing front-rear polarity.
Ras 样 GTP 酶 MglA 是杆状粘细菌前后极性的关键调节因子。MglA-GTP 定位于细胞的前极，刺激两种依赖 IV 型菌毛的运动和滑行运动的机制组装。MglA-GTP 的定位受到其同源 GEF RomR/RomX 复合物和 GAP MglB Roadblock 结构域蛋白的空间限制。矛盾的是，RomR/RomX 和 MglB 分别以低浓度和高浓度定位于前极和后极。然而，通过未知的机制，GEF 活性在前极占主导地位，GAP 活性在后极占主导地位。在这里，我们鉴定了 RomY，并表明它刺激 MglB 的 GAP 活性。MglB/RomY 相互作用的亲和力低，将二聚体 MglB/RomY GAP 复合物的形成几乎完全限制在后极，此时 MglB 浓度较高。我们的数据支持这样一种模型，即 RomY 通过与 MglB 形成低亲和力复合物，确保高 MglB/RomY GAP 活性局限于后极，在后极它占主导地位并与 RomR/RomX 复合物的 GEF 活性竞争。因此，MglA-GTP 的定位被限制在前极，从而建立前后极性。
