“Disruptor” residues in the regulator of g protein signaling (RGS) R12 subfamily attenuate the inactivation of g subunits

Understanding the molecular basis of interaction specificity between RGS (regulator of G protein signaling) proteins and heterotrimeric () G proteins would enable the manipulation of RGS-G protein interactions, explore their functions, and effectively target them therapeutically. RGS proteins are classified into four subfamilies (R4, R7, RZ, and R12) and function as negative regulators of G protein signaling by inactivating G subunits. We found that the R12 subfamily members RGS10 and RGS14 had lower activity than most R4 subfamily members toward the G_i subfamily member G_o. Using structure-based energy calculations with multiple G-RGS complexes, we identified R12-specific residues in positions that are predicted to determine the divergent activity of this subfamily. This analysis predicted that these residues, which we call “disruptor residues,” interact with the G helical domain. We engineered the R12 disruptor residues into the RGS domains of the high-activity R4 subfamily and found that these altered proteins exhibited reduced activity toward G_o. Reciprocally, replacing the putative disruptor residues in RGS18 (a member of the R4 subfamily that exhibited low activity toward G_o) with the corresponding residues from a high-activity R4 subfamily RGS protein increased its activity toward G_o. Furthermore, the high activity of the R4 subfamily toward G_o was independent of the residues in the homologous positions to the R12 subfamily and RGS18 disruptor residues. Thus, our results suggest that the identified RGS disruptor residues function as negative design elements that attenuate RGS activity for specific G proteins.