A site on rod G protein α subunit that mediates effector activation

Abstract

The heterotrimeric guanine nucleotide binding proteins (G proteins) are activated by sensory or hormone receptors. In turn, the G proteins activate effector proteins such as adenylyl cyclase, cyclic guanosine 3′,5′-monophosphate phosphodiesterase (cGMP PDE), phospholipase C, and potassium and calcium ion channels by mechanisms that are poorly understood. A site on the a subunit of the G protein transducin (αt) has been identified that interacts with and activates cGMP phosphodiesterase, the effector enzyme in rod photoreceptors. A22-amino acid peptide, corresponding to residues 293 to 314 from the COOH-terminal region of at, fully mimicked at and potently activated PDE. This region is adjacent to the receptor activation domain; thus, the α subunit of this G protein has a site for interaction with both its effector and receptor that maps near the COOH-terminus.