A bipartite, low-affinity roadblock domain-containing GAP complex regulates bacteria front-rear polarity

The Ras-like GTPase MglA is a key regulator of front-rear polarity in the rod-shaped Myxococcus xanthus cells. MgIA-GTP localizes to the leading cell pole and stimulates assembly of the two machineries for type IV pili-dependent motility and gliding motility. MgIA-GTP localization is spatially constrained by its cognate GEF, the RomR/RomX complex, and GAP, the MgIB Roadblock-domain protein. Paradoxically, RomR/RomX and MgIB 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 MgIB GAP activity. The MgIB/RomY interaction is low affinity, restricting formation of the bipartite MgIB/RomY GAP complex almost exclusively to the lagging pole with the high MgIB concentration. Our data support a model wherein RomY, by forming a low-affinity complex with MgIB, ensures that the high MgIB/RomY GAP activity is confined to the lagging pole where it dominates and outcompetes the GEF activity of the RomR/RomX complex. Thereby, MgIA-GTP localization is constrained to the leading pole establishing front-rear polarity.

Automated summary

MglA-GTP is a key regulator of front-rear polarity in Myxococcus xanthus cells, and it localizes to the leading pole to stimulate assembly of the machinery for type IV pili-dependent motility and gliding motility. RomY stimulates the GAP activity of MgIB, and its low-affinity interaction ensures that the high MgIB/RomY GAP activity is confined to the lagging pole.