title: Protein phosphatase 2A is reversibly modified by methyl esterification at its C-terminal leucine residue in bovine brain.
abstract: We have recently described a novel protein carboxyl methylation system that results in the reversible modification of a 36-kDa polypeptide component of a 178-kDa protein in the cytosol of a variety of eucaryotic cells. This reaction, catalyzed by a cytosolic 40-kDa methyl-transferase, results in the methyl esterification of the alpha-carboxyl group of the C-terminal leucine residue. We have now purified the major methylated 36-kDa polypeptide from bovine brain. N-terminal sequence analysis of a tryptic fragment of this polypeptide revealed identity to the catalytic subunit of protein phosphatase 2A. This enzyme exists in the cell predominantly as a trimeric 151-kDa native species containing the 36-kDa catalytic polypeptide that terminates in a leucine residue. We then fractionated bovine brain cytosolic extracts to separate the major phosphatase isoforms 2A1 and 2A2 and found that both could be methylated by a partially purified preparation of the methyltransferase. A synthetic C-terminal octapeptide based on the sequence of the 36-kDa catalytic subunit is neither a substrate nor an inhibitor of this methyltransferase, suggesting that this enzyme recognizes aspects of the tertiary and/or quaternary structure of the native phosphatase. Because this modification reaction is readily reversible in extracts, it may represent a novel strategy of the cell to modulate the function of this protein phosphatase.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles 90024-1569.
authors.forename: H
authors.initials: H
authors.lastname: Xie
authors.forename: S
authors.initials: S
authors.lastname: Clarke
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D007527:Isoenzymes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D046911:Macromolecular Substances; D008745:Methylation; D008970:Molecular Weight; D010449:Peptide Mapping; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010762:Phosphorylase a / Q000378:metabolism; D011496:Protein Methyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D011497:Protein O-Methyltransferase / Q000302:isolation & purification / Q000378:metabolism*; D054648:Protein Phosphatase 2
chemical_list: D007527:Isoenzymes; D046911:Macromolecular Substances; C085457:C-terminal leucine protein methyltransferase; D011496:Protein Methyltransferases; D011497:Protein O-Methyltransferase; D010762:Phosphorylase a; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D007930:Leucine