title: The role of G protein methylation in the function of a geranylgeranylated beta gamma isoform.
abstract: The gamma subunit of heterotrimeric G proteins is isoprenylated and methylated on its carboxyl terminal cysteine residue. While retinal transducin is farnesylated, all other gamma subunits are modified by geranylgeranylation. An immobilized form of pig liver esterase (iPLE) is able to hydrolyze the methyl ester of a geranylgeranylated beta gamma isoform (beta 1 gamma 2). Since methylation is the only reversible reaction in the isoprenylation pathway, it could be a site of regulation of G protein activity. With both the methylated and demethylated beta 1 gamma 2 now available, the role of methylation for a geranylgeranylated heterotrimeric G protein may be addressed. Here, it is reported that methylation has no effect on the ability of beta gamma to interact with an alpha subunit, as probed by ADP-ribosylation studies with pertussis toxin, and has a small effect (less than 2-fold) on the ability of geranylgeranylated beta gamma to activate phosphatidylinositol-specific phospholipase C (PIPLC) and phosphoinositide 3 kinase (PI3K). In binding studies, demethylation only slightly decreased the ability of beta 1 gamma 2 to adhere to azolectin vesicles. Therefore, methylation of heterotrimeric G proteins appears to have only a minor effect in signal transduction processes which can be correlated to a decrease in hydrophobicity of the beta gamma subunit.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Parish
authors.forename: A V
authors.initials: AV
authors.lastname: Smrcka
authors.forename: R R
authors.initials: RR
authors.lastname: Rando
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003545:Cysteine; D004800:Enzymes, Immobilized / Q000378:metabolism; D004950:Esterases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D046911:Macromolecular Substances; D008745:Methylation; D037342:Pertussis Toxin; D010713:Phosphatidylcholines; D019869:Phosphatidylinositol 3-Kinases; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010743:Phospholipids; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D017368:Protein Prenylation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D018411:Spodoptera; D013552:Swine; D015293:Transducin / Q000737:chemistry* / Q000378:metabolism*; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D004800:Enzymes, Immobilized; D046911:Macromolecular Substances; D010713:Phosphatidylcholines; D010743:Phospholipids; D011994:Recombinant Proteins; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; C024990:asolectin; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D004950:Esterases; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D019204:GTP-Binding Proteins; D015293:Transducin; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D003545:Cysteine