Receptor-effector coupling by G proteins: implications for normal and abnormal signal transduction.

I. Introduction THE ROLE of heterotrimeric guanine nucleotide binding proteins (G proteins) in signal transduction was first covered in Endocrine Reviews in 1981, when three distinct G proteins involved in visual transduction and regulation of cAMP formation were recognized (1). This topic was updated in Endocrine Reviews in 1989 by which time the number of mammalian G proteins identified had doubled, and their roles in regulation of various phospholipases and ion channels had been recognized (2). Barely 3 years later, the number of distinct mammalian G proteins recognized has again doubled, multiple G proteins have been identified in invertebrates, plants, and single-celled eukaryotes, and the number of cellular functions shown to be regulated by G proteins has increased correspondingly. Numerous excellent reviews covering various aspects of this topic have recently appeared (3–9), but given the rapidity of progress in this field, an update in Endocrine Reviews appears timely. This review summarizes rece...