Regulators of G‐protein Signaling Proteins: Conformational Dynamics and Allosteric Control

Abstract

Regulators of G-protein signaling (RGS) proteins are intracellular proteins that negatively modulate the signaling pathways of G-protein coupled receptors (GPCRs). Because RGS proteins directly bind to activated G-proteins and accelerate the rate of GTP-hydrolysis, they have emerged as potential drug targets for regulating GPCR signaling. While conventional approaches have been focused on directly targeting RGS-Gα protein-protein interaction using small molecules, new approaches that target allosteric sites are emerging. In this work, we have studied using atomistic simulations the mechanism of action of a small molecule that binds, with differing affinity, to specific cysteine residues on two structurally homologous RGS proteins, RGS4 and RGS8. We find that each RGS protein has flexibility in a pair of helices that allows small molecule to access buried cysteine residues. Such flexibility only became apparent on application of enhanced sampling simulations on apo-RGS structures. Moreover, we observe that the small molecule can spontaneously bind to “conformationally-open” RGS proteins, but only associates with different surface sites in “conformationally-closed” RGS proteins. The binding of small molecule to a buried cysteine residue on each protein also appears to perturb the protein-protein interface in each RGS-Gα complex via an allosteric mechanism.