Isoprenylation of C-terminal cysteine in a G-protein gamma subunit.
The predicted amino acid sequences for the Gi alpha 1 and G gamma 6 subunits of brain heterotrimeric G-proteins both contain C-terminal Cys-A-A-X elements (A is an aliphatic residue and X is any amino acid). This domain represents the site of Cys thioether modification by isoprenoids in p21ras, nuclear lamins, and fungal mating factors. We now show that G gamma 6, translated in reticulocyte lysate, is efficiently labeled with the isoprenoid precursor, [3H]mevalonate. Alteration of the sequence of G gamma 6 so that a Gly was substituted for Cys in the C-terminal Cys-A-A-X element rendered the protein incapable of undergoing isoprenoid modification. In contrast to G gamma 6, the Gi alpha 1 subunit did not appear to undergo isoprenylation when translated in reticulocyte lysate. Transient expression of the protein in COS cells, which were able to isoprenylate the p21 product of transfected H-ras, also failed to demonstrate isoprenylation of Gi alpha 1. The modification of the gamma subunit by a hydrophobic moiety may have important implications for the assembly of the brain G-protein beta gamma complexes into the cell membrane.
Maltese
W A
WA
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822.
Robishaw
J D
JD
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002474:Cell-Free System; D003001:Cloning, Molecular; D003545:Cysteine / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D013729:Terpenes
D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D013729:Terpenes; D019204:GTP-Binding Proteins; D003545:Cysteine