Expansion of signal transduction by G proteins -: The second 15 years or so:: From 3 to 16 α subunits plus βγ dimers

The first 15 years, or so, brought the realization that there existed a G protein coupled signal transduction mechanism by which hormone receptors regulate adenylyl cyclases and the light receptor rhodopsin activates visual phosphodiesterase. Three G proteins, Gs, Gi and transducin (T) had been characterized as alpha beta-gamma heterotrimers, and Gs alpha-GTP and T alpha-GTP had been identified as the sigaling arms of Gs and T. These discoveries were made using classical biochemical approaches, and culminated in the purification of these G proteins. The second 15 years, or so, are the subject of the present review. This time coincided with the advent of powerful recombinant DNA techniques. Combined with the classical approaches, the field expanded the repertoire of G proteins from 3 to 16, discovered the superfamily of seven transmembrane G protein coupled receptors (GPCRs) - which is not addressed in this article - and uncovered an amazing repertoire of effector functions regulated not only by alpha GTP complexes but also by beta gamma dimers. Emphasis is placed in presenting how the field developed with the hope of conveying why many of the new findings were made. (c) 2006 Elsevier B.V. All rights reserved.