Interaction of class A G protein-coupled receptors with G proteins.

A model for interaction of class A G protein-coupled receptor with the G protein G(alpha) subunit is proposed using the rhodopsin-transducin (RD/Gt) prototype. The model combines the resolved interactions/distances, essential in the active RD*/Gt system, with the structure of Gt(alpha) C-terminal peptide bound to RD* while stabilizing it. Assuming the interactions involve conserved parts of the partners, the model specifies the conserved Helix 2 non-polar X- - -X, Helix 3 DRY and Helix 7/8 NP- -Y- - F RD* motifs interacting with the Gt(alpha) C-terminal peptide, in compliance with the structure of the latter. A concomitant role of Gt(alpha) and Gt(gamma) C-termini in stabilizing RD* could possibly be resolved assuming a receptor dimer as requisite for G protein activation.