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 is 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. These 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.