RECEPTOR-EFFECTOR COUPLING BY G-PROTEINS

The primary structure of G proteins as deduced from purified proteins and cloned subunits is presented. When known, their functions are discussed, as are recent data on direct regulation of ionic channels by G proteins. Experiments on expression of α subunits, either in bacteria or by in vitro translation of mRNA synthesized from cDNA are presented as tools for definitive assignment of function to a given G protein. The dynamics of G protein-mediated signal transduction are discussed. Key points include the existence of two superimposed regulatory cycles in which upon activation by GTP, G proteins dissociate into α and βγ and their dissociated α subunits hydrolyze GTP. The action of receptors to catalyze rather than regulate by allostery the activation of G proteins by GTP is emphasized, as is the role of subunit dissociation, without which receptors could not act as catalysts. Current views of intramembrane networking of G protein-mediated receptor-effector coupling are discussed. To facilitate the reading of this review, we have presented the various subtopics of this rapidly expanding field in sections I-IX, each of which is organized as a self-contained sub-chapter that can be read independently of the others. © 1990.