An N-terminal region of Caenorhabditis elegans RGS proteins EGL-10 and EAT-16 directs inhibition of Gαo versus Gαq signaling

Abstract

Regulator of G protein signaling (RGS) proteins contain an RGS domain that inhibits Gα signaling by activating Gα GTPase activity. Certain RGS proteins also contain a Gγ-like (GGL) domain and a poorly characterized but conserved N-terminal region. We assessed the functions of these subregions in the Caenorhabditis elegans RGS proteins EGL-10 and EAT-16, which selectively inhibit GOA-1 (Gαo) and EGL-30 (Gαq), respectively. Using transgenes in C. elegans, we expressed EGL-10, EAT-16, their subregions, or EGL-10/EAT-16 chimeras. The chimeras showed that the GGL/RGS region of either protein can act on either GOA-1 or EGL-30 and that a key factor determining Gα target selectivity is the manner in which the N-terminal and GGL/RGS regions are linked. We also found that coexpressing N-terminal and GGL/RGS fragments of EGL-10 gave full EGL-10 activity, whereas either fragment alone gave little activity. Biochemical analysis showed that coexpressing the two fragments caused both to increase in abundance and also caused the GGL/RGS fragment to move to the membrane, where the N-terminal fragment is localized. By coimmunoprecipitation, we found that the N-terminal fragment complexes with the C-terminal fragment and its associated Gβ subunit, GPB-2. We conclude that the N-terminal region directs inhibition of Gα signaling by forming a complex with the GGL/RGS region and affecting its stability, membrane localization, and Gα target specificity.