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

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The guanine-nucleotide binding regulatory proteins (G-proteins) are alpha1beta1gamma1 heterotrimers which function as transmembrane signal transducers by coupling receptor 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 by a betagamma 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 betagamma complex is becoming increasingly apparent in several systems. The present research emphasized the role of the betagamma complex in G-protein-mediated signal transduction. We have used subunit specific peptide antibodies to probe regions of the betagamma 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 betagamma complex in both transient and stable transfected cell systems. These studies may elucidate the contribution of the betagamma subunit complex to the receptor and effector selectivity characteristic of G-proteins and to the adaptive responses pursuant to agonist stimulation.