Conformational Evolution of Three Regulator of G-Protein Signaling Proteins (RGS4, RGS8, RGS19) in Microsecond-Scale Simulations

Abstract

Regulators of G protein signaling (RGS) proteins modulate GPCR signaling by binding to Gα-subunits of heterotrimeric G proteins and accelerating hydrolysis of GTP. Therefore, RGS proteins are becoming increasingly important therapeutic targets to be directly or allosterically inhibited from binding to Gα-subunits. While structures of several known RGS proteins are highly similar and largely contain α-helical motifs, some thiadiazolidinone (TDZD) compounds that target cysteine residues have shown different levels of specificities and potencies for closely related proteins thereby suggesting intrinsic differences in dynamics of these proteins. In this work, we have studied the dynamics of three different RGS proteins (apo-RGS4, apo-RGS8, and apo-RGS19) using microsecond-scale classical molecular dynamics (MD) simulations with CHARMM and AMBER force-fields. Analyses of these trajectories reveal high fluctuations in α5 and α6 helices and the loops connecting them. These fluctuations lead to perturbations in residues in the RGS-Gα interface and in the vicinity of cysteines that are targets of allosteric inhibitors. These findings have significant implications for understanding differences in potencies and specificities of inhibitory small-molecules.