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

Abstract

The Ras-like GTPase MglA is a key regulator of front-rear polarity in rod-shaped Myxococcus xanthus cells. MglA-GTP localizes to the leading cell pole and stimulates assembly of the two motility machineries. MglA-GTP localization is spatially constrained by its cognate GEF, the RomR/RomX complex, and GAP, the MglB Roadblock-domain protein. 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 as a co-GAP that stimulates MglB GAP activity. The MglB/RomY interaction is low affinity, restricting complex formation 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 MglB GAP activity is spatially precisely confined to the lagging pole, thereby constraining MglA-GTP to the leading pole establishing front-rear polarity.