title: Mutation of Tyr307 and Leu309 in the protein phosphatase 2A catalytic subunit favors association with the alpha 4 subunit which promotes dephosphorylation of elongation factor-2.
abstract: The cellular location and substrate specificity of the catalytic subunit (C) of protein phosphatase 2A (PP2A) depend on its interaction with A and B subunits. The distribution of epitope-tagged wild-type or mutated C subunits was studied by transient expression in COS-7 cells. Wild-type tagged C expressed at low levels formed ABC trimer and AC dimer like the endogenous C. Single mutations of C at the site of phosphorylation (Y307F) or carboxymethylation (L309Q) resulted in recovery of only AC dimer. Double mutation of both residues resulted in association of C with alpha 4 protein (alpha 4), a novel subunit of PP2A, instead of with A and B subunits. Thus, the distribution of C between ABC trimer, AC dimer, and alpha 4C complexes can be affected by modifications of the C-terminal residues. The alpha 4 protein is a homologue of the yeast Tap42 protein that functions downstream of the TOR protein to regulate protein synthesis. Transient overexpression of FLAG-alpha 4 resulted in increased dephosphorylation of elongation factor 2, but had no effect on phosphorylation of either p70S6 kinase or PHAS-I (eIF4E-BP). Signals that affect phosphorylation or methylation of the C subunit of PP2A may promote subunit exchange and direct phosphatase activity to specific intracellular substrates.
authors.affiliation: Center for Cell Signaling, The University of Virginia, Charlottesville 22908, USA.
authors.forename: H
authors.initials: H
authors.lastname: Chung
authors.forename: A C
authors.initials: AC
authors.lastname: Nairn
authors.forename: K
authors.initials: K
authors.lastname: Murata
authors.forename: D L
authors.initials: DL
authors.lastname: Brautigan
mesh_terms: D000818:Animals; D000837:Anion Exchange Resins; D001426:Bacterial Proteins; D019556:COS Cells; D020134:Catalytic Domain / Q000235:genetics*; D002852:Chromatography, Ion Exchange; D006388:Hemagglutinins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D037102:Lectins; D007930:Leucine / Q000235:genetics* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009842:Oligopeptides / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D054648:Protein Phosphatase 2; D012117:Resins, Synthetic; D014162:Transfection; D014443:Tyrosine / Q000235:genetics* / Q000378:metabolism
chemical_list: D000837:Anion Exchange Resins; D001426:Bacterial Proteins; D006388:Hemagglutinins; D037102:Lectins; D009842:Oligopeptides; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D010455:Peptides; D010750:Phosphoproteins; D012117:Resins, Synthetic; C114923:hemagglutinin A, Porphyromonas gingivalis; D014443:Tyrosine; C042855:Mono Q; C085706:FLAG peptide; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D007930:Leucine