Abstract
The G protein β subunit Gβ 5 deviates significantly from the other four members of Gβ -subunit family in amino acid sequence and subcellular localization. To detect the protein targets of Gβ 5 in vivo, we have isolated a native Gβ 5 protein complex from the retinal cytosolic fraction and identified the protein tightly associated with Gβ 5 as the regulator of G protein signaling (RGS) protein, RGS7. Here we show that complexes of Gβ 5 with RGS proteins can be formed in vitro from the recombinant proteins. The reconstituted Gβ 5-RGS dimers are similar to the native retinal complex in their behavior on gel-filtration and cation-exchange chromatographies and can be immunoprecipitated with either anti-Gβ 5 or anti-RGS7 antibodies. The specific Gβ 5-RGS7 interaction is determined by a distinct domain in RGS that has a striking homology to Gγ subunits. Deletion of this domain prevents the RGS7-Gβ 5 binding, although the interaction with Gα is retained. Substitution of the Gγ -like domain of RGS7 with a portion of Gγ 1 changes its binding specificity from Gβ 5 to Gβ 1. The interaction of Gβ 5 with RGS7 blocked the binding of RGS7 to the Gα subunit Gα o, indicating that Gβ 5 is a specific RGS inhibitor.
