Research ArticleG Protein Signaling

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

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Sci. Signal.  12 Jun 2018:
Vol. 11, Issue 534, eaan3677
DOI: 10.1126/scisignal.aan3677

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Designing specificity

Once an agonist binds to its G protein–coupled receptor, GTP replaces GDP on the α subunit of an associated G protein, which then dissociates from its βγ dimer to activate effectors. The GTPase activity of the α subunit returns the G protein to an inactive state, a process that is accelerated by interactions with members of the regulator of G protein signaling (RGS) family. Asli et al. used functional and structural analyses to identify specific amino acid residues that distinguished RGS proteins with low activity toward Gαo from those with high activity. High-activity RGS proteins that were mutated to contain these “disruptor” residues exhibited reduced inhibitory activity toward the Gα subunit. Together, these data suggest that “disruptor” residues within RGS proteins may encode specificity toward Gα subunits.

Abstract

Understanding the molecular basis of interaction specificity between RGS (regulator of G protein signaling) proteins and heterotrimeric (αβγ) 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 Gα subunits. We found that the R12 subfamily members RGS10 and RGS14 had lower activity than most R4 subfamily members toward the Gi subfamily member Gαo. Using structure-based energy calculations with multiple Gα-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 Gα 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 Gαo. Reciprocally, replacing the putative disruptor residues in RGS18 (a member of the R4 subfamily that exhibited low activity toward Gαo) with the corresponding residues from a high-activity R4 subfamily RGS protein increased its activity toward Gαo. Furthermore, the high activity of the R4 subfamily toward Gαo 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 Gα proteins.

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