Enzymatic methylation of 23-29-kDa bovine retinal rod outer segment membrane proteins. Evidence for methyl ester formation at carboxyl-terminal cysteinyl residues

J Biol Chem. 1989 Aug 5;264(22):12879-84.


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 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).

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cattle
  • Cell Membrane / metabolism
  • Cysteic Acid / metabolism
  • Cysteine / metabolism*
  • Hydrolysis
  • Membrane Proteins / metabolism*
  • Methylation
  • Molecular Weight
  • Peptides / metabolism
  • Photoreceptor Cells / enzymology*
  • Protein Methyltransferases / metabolism*
  • Protein O-Methyltransferase / metabolism*
  • Rod Cell Outer Segment / enzymology*
  • Rod Cell Outer Segment / metabolism
  • Tritium


  • Membrane Proteins
  • Peptides
  • Tritium
  • Cysteic Acid
  • Protein Methyltransferases
  • Protein O-Methyltransferase
  • Cysteine