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Membrane-Binding Domain of the Small G Protein G25K Contains an S-(all- Trans-Geranylgeranyl)Cysteine Methyl Ester at its Carboxyl Terminus
Harvey K. Yamane, Christopher C. Farnsworth, Hongying Xie, Tony Evans, William N. Howald, Michael H. Gelb, John A. Glomset, Steven Clarke and Bernard K.-K. Fung
Proceedings of the National Academy of Sciences of the United States of America
Vol. 88, No. 1 (Jan. 1, 1991), pp. 286-290
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2355755
Page Count: 5
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We showed previously that a 23-kDa guanine nucleotide-binding protein (G protein) purified from bovine brain membranes is carboxyl methylated and that this modification occurs at or near the membrane-binding domain. In the present study, we identified this small G protein as G25K (formerly termed Gp). We demonstrated that proteolytic digests of 3H-methylated G25K contained radiolabeled material that coeluted with synthetic S-(geranylgeranyl)cysteine methyl ester on reversed-phase HPLC. Further treatment by performic acid oxidation yielded radiolabeled material that coeluted with L-cysteic acid methyl ester, verifying that the isoprenoid moiety and carboxyl methyl ester are localized on a C-terminal cysteine residue. Analysis by gas chromatography-coupled mass spectrometry of material released from purified G25K by Raney nickel treatment positively identified the covalently bound lipid as an all-trans-geranylgeranyl (C20) isoprenoid moiety. These results suggest that geranylgeranyl modification and perhaps methyl esterification function in the membrane localization of this small G protein.
Proceedings of the National Academy of Sciences of the United States of America © 1991 National Academy of Sciences