Identification of the Gβ5-RGS7 protein complex in the retina

The G protein β subunit Gβ5 deviates significantly from the four other members of the Gβ family in amino acid sequence, unique expression pattern (only in the CNS), and cytosolic localization. To identify the members of the Gβ5-mediated signaling pathway, we purified the native protein complex containing Gβ5 from the cytosolic fraction of bovine retina. Analysis of the isolated complex revealed that Gβ5 is tightly associated with RGS7, a member of the superfamily of negative regulators of G protein signaling. This finding, for the first time, demonstrates an interaction between a Gβ subunit and an RGS protein. Gβ5 was not detected in the outer segments of photoreceptor cells, suggesting that the cytosolic Gβ5-RGS7 complex is not directly involved in phototransduction.