Enzymatic methylation of 23-29-kDa bovine retinal rod outer segment membrane proteins. Evidence for methyl ester formation at carboxyl-terminal cysteinyl residues.
A group of 23-29-kDa polypeptides in the membranes of bovine rod outer segments are substrates for S-adenosylmethionine-dependent methylation reactions. The bulk of the methyl group incorporation is in base-labile ester-like linkages, and does not appear to be due to the widespread D-aspartyl/L-isoaspartyl methyltransferase (EC 2.1.1.77). To determine the site(s) of methylation, 3H-methylated proteins separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate were eluted and digested with papain, leucine aminopeptidase-M, and prolidase. After performic acid oxidation of the digest, a base-labile radioactive material was recovered that coeluted with a synthetic standard of cysteic acid methyl ester upon cation exchange and G-15 gel filtration chromatography, as well as in two thin-layer electrophoresis and two thin-layer chromatography systems. These results provide direct evidence for the methylation of the alpha-carboxyl group of a carboxyl-terminal cysteinyl residue, a modification that has been proposed for the 21-kDa Ha-ras product and other cellular proteins (Clarke, S., Vogel, J. P., Deschenes, R. J., and Stock, J. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 4643-4647).
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Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
Clarke
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D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D003544:Cysteic Acid / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism*; D006868:Hydrolysis; D008565:Membrane Proteins / Q000378:metabolism*; D008745:Methylation; D008970:Molecular Weight; D010455:Peptides / Q000378:metabolism; D010786:Photoreceptor Cells / Q000201:enzymology*; D011496:Protein Methyltransferases / Q000378:metabolism*; D011497:Protein O-Methyltransferase / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000201:enzymology* / Q000378:metabolism; D014316:Tritium
D008565:Membrane Proteins; D010455:Peptides; D014316:Tritium; D003544:Cysteic Acid; D011496:Protein Methyltransferases; D011497:Protein O-Methyltransferase; D003545:Cysteine