GUANINE NUCLEOTIDE BINDING PROTEIN BETA-GAMMA DIMERS--STRUCTURE AND FUNCTION

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The guanine-nucleotide binding regulatory proteins (G-proteins) are alpha-1-beta-1-gamma-1 heterotrimers which function as transmembrane signal transducers by coupling receptors for extracellular stimuli to intracellular effectors (enzymes, ion channels). G-proteins constitute a diverse family distinguished by specific receptor and effector interactions which in turn are determined by the structure of the three constituent subunits. The alpha subunit binds guanine nucleotides and has a well established role in effector modulation. The beta and gamma subunits are tightly associated as a beta/gamma complex, comprising a single functional entity which, like the alpha subunit, is absolutely required for G-protein interaction with receptor. An effector modulatory role for the beta/gamma complex s becoming increasingly apparent in several systems. The present research emphasizes the role of the beta/gamma complex in G-protein-mediated signal transduction. We have used subunit specific peptide antibodies to probe regions of the beta/gamma complex important for functional interaction with the alpha subunit and to monitor expression of recombinant subunits. Site-directed mutagenesis has been used to study the assembly, processing and effector function of the beta/gamma complex in both transient and stable transfected cell systems. The studies may elucidate the contribution of the beta/gamma subunit complex to the receptor and effector selectivity characteristic of G-proteins and to the adaptive responses pursuant to agonist stimulation.