Phosphorylation of Gz alpha by protein kinase C blocks interaction with the beta gamma complex.
Gz alpha is a G protein alpha subunit with biochemical properties that distinguish it from other members of the G protein alpha subunit family. One such property is its ability to be stoichiometrically phosphorylated by protein kinase C (PKC), both in vitro and in intact cells. The site of this phosphorylation has been mapped to a region near the N terminus of Gz alpha, but no functional significance of the modification has been established. To investigate this question, we have developed a baculovirus/Sf9 cell expression system to produce Gz alpha. The protein purified from Sf9 cells is functional as assessed by its ability both to bind guanine nucleotide in a Mg(2+)-sensitive fashion and to serve as a substrate for phosphorylation by PKC. Furthermore, addition of the G protein beta gamma complex purified from bovine brain inhibits phosphorylation of Gz alpha in a dose-dependent manner. Conversely, phosphorylation of Gz alpha inhibits its ability to interact with beta gamma subunits. These results establish a functional consequence for PKC-catalyzed phosphorylation of Gz alpha and suggest a mechanism for regulation of signaling through Gz by preventing reassociation of its subunits.
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Department of Molecular Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710-3686, USA.
Casey
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PJ
D000818:Animals; D016367:Baculoviridae; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D018411:Spodoptera; D014162:Transfection
D046911:Macromolecular Substances; D011994:Recombinant Proteins; D011493:Protein Kinase C; D019204:GTP-Binding Proteins