Guanine Nucleotide Binding Proteins and Signal Transduction

This chapter discusses the general aspects and functions of guanine nucleotide binding proteins and signal transduction. The function of several identified G-proteins such as G_o and the multiple forms of “G_i” are also defined. The function of ras and ras-related gene products likewise are also elucidated in the chapter. The G-protein(s) linked to stimulation of PI breakdown are identified. Members of the G-protein family share certain common features. G- Proteins act to couple receptors and effectors. The receptors with which G-proteins interact appear to be transmembrane glycoproteins capable of being activated by specific extracellular signals or “first messengers.” These signals are diverse and include peptide and glycoprotein hormones, neurotransmitter amines, prostaglandins, chemical odorants, photons of light, and perhaps others. Activation of the receptor involves more than specific binding. New G-proteins, and new functions for G-proteins, are also discovered. G-protein-effector interaction is transient under physiologic conditions and is terminated by a guanosine triphosphatase (GTPase) activity intrinsic to the G-protein. The structural basis for receptor-G-protein-effector interactions and the specificity of these interactions are reviewed. Novel therapeutic approaches could result from an appreciation of these structural and functional details.