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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
Stable URL: http://www.jstor.org/stable/2355755
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Membrane-Binding Domain of the Small G Protein G25K Contains an S-(all- Trans-Geranylgeranyl)Cysteine Methyl Ester at its Carboxyl Terminus
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Abstract

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.

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