Identification of a novel activator of GOA‐1, a trimeric G protein critical for early stages of C. elegans development

Abstract

Classical activation of trimeric G proteins occurs via guanine nucleotide exchange factor (GEF) activity of GPCRs. However, it has become recently evident that a set of non‐receptor proteins can also activate G proteins. Among these non‐receptor GEFs, GIV is the first one that activates G proteins via a defined motif, i.e., the Gα‐Binding and Activating (GBA) motif. We investigated if a similar GBA motif capable of activating G proteins is present in other unrelated proteins. Our bioinformatics searches revealed a putative GBA sequence in an uncharacterized protein highly expressed in early stages of C. elegans development. Here we demonstrate that this protein, that we call ceGBA, binds directly to GOA‐1, a G protein critical for C. elegans development. By using a combination of site directed‐mutagenesis, homology modeling and biochemistry we demonstrate that ceGBA utilizes its GBA motif to bind to the switch II/α3 helix hydrophobic pocket of inactive GOA‐1 and subsequently activates the G protein by accelerating the rate of nucleotide exchange. These results not only suggest a novel receptor‐independent mechanism of GOA‐1 activation during organismal development but also demonstrate that the GBA motif is a functional module for G protein activation conserved among divergent proteins across evolution.