A Conserved Protein Interaction Interface on the Type 5 G Protein β Subunit Controls Proteolytic Stability and Activity of R7 Family Regulator of G Protein Signaling Proteins

Morwenna Y Porter,Keqiang Xie,Edwin Pozharski,Michael R Koelle,Kirill A Martemyanov

doi:10.1074/jbc.m110.163600

Abstract

Regulators of G protein signaling (RGS) proteins of the R7 subfamily limit signaling by neurotransmitters in the brain and by light in the retina. They form obligate complexes with the Gβ5 protein that are subject to proteolysis to control their abundance and alter signaling. The mechanisms that regulate this proteolysis, however, remain unclear. We used genetic screens to find mutations in Gβ5 that selectively destabilize one of the R7 RGS proteins in Caenorhabditis elegans. These mutations cluster at the binding interface between Gβ5 and the N terminus of R7 RGS proteins. Equivalent mutations within mammalian Gβ5 allowed the interface to still bind the N-terminal DEP domain of R7 RGS proteins, and mutant Gβ5-R7 RGS complexes initially formed in cells but were then rapidly degraded by proteolysis. Molecular dynamics simulations suggest the mutations weaken the Gβ5-DEP interface, thus promoting dynamic opening of the complex to expose determinants of proteolysis known to exist on the DEP domain. We propose that conformational rearrangements at the Gβ5-DEP interface are key to controlling the stability of R7 RGS protein complexes.

Highlights

G protein pathways are ubiquitous signaling systems that provide control over virtually all cellular functions [1, 2]
A Novel Allele of GPB-2/G␤5 Causes Hyperactive Behavior in C. elegans—To further our understanding of the mechanisms that regulate G protein signaling, we performed a genetic screen for animals hyperactive for egg laying, a behavior controlled by R7 RGS1⁄7G␤5 complexes [23]
We provide insights into the molecular mechanisms involved in post-translational control of R7 regulator of G protein signaling (RGS) protein expression

Summary

Introduction

G protein pathways are ubiquitous signaling systems that provide control over virtually all cellular functions [1, 2]. Equivalent mutations within mammalian G␤5 allowed the interface to still bind the N-terminal DEP domain of R7 RGS proteins, and mutant G␤5-R7 RGS complexes initially formed in cells but were rapidly degraded by proteolysis.

Results

Conclusion