Residue-level determinants of RGS R4 subfamily GAP activity and specificity towards the Gi subfamily

The structural basis for the GTPase-accelerating activity of regulators of G protein signaling (RGS) proteins, as well as the mechanistic basis for their specificity in interacting with the heterotrimeric (alpha beta gamma) G proteins they inactivate, is not sufficiently understood at the family level. Here, we used biochemical assays to compare RGS domains across the RGS family and map those individual residues that favorably contribute to GTPase-accelerating activity, and those residues responsible for attenuating RGS domain interactions with G alpha subunits. We show that conserved interactions of RGS residues with both the G alpha switch I and II regions are crucial for RGS activity, while the reciprocal effects of modulatory and disruptor residues selectively modulate RGS activity. Our results quantify how specific interactions between RGS domains and G alpha subunits are set by a balance between favorable RGS residue interactions with particular G alpha switch regions, and unfavorable interactions with the G alpha helical domain.

Automated summary

The study compared RGS domains across the family and identified key interactions between RGS residues and G alpha switch regions. Modulatory and disruptor residues selectively modulated RGS activity.