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

Biochemistry. 1999 Aug 10;38(32):10371-6. doi: 10.1021/bi990902g.


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.

Publication types

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

MeSH terms

  • Animals
  • Anion Exchange Resins
  • Bacterial Proteins*
  • COS Cells
  • Catalytic Domain / genetics*
  • Chromatography, Ion Exchange
  • Hemagglutinins / genetics
  • Hemagglutinins / isolation & purification
  • Hemagglutinins / metabolism
  • Lectins
  • Leucine / genetics*
  • Leucine / metabolism
  • Mutagenesis, Site-Directed
  • Oligopeptides / biosynthesis
  • Oligopeptides / genetics
  • Oligopeptides / metabolism
  • Peptide Elongation Factor 2
  • Peptide Elongation Factors / metabolism*
  • Peptides / genetics
  • Peptides / metabolism
  • Phosphoprotein Phosphatases / genetics*
  • Phosphoprotein Phosphatases / isolation & purification
  • Phosphoprotein Phosphatases / metabolism
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Precipitin Tests
  • Protein Phosphatase 2
  • Resins, Synthetic
  • Transfection
  • Tyrosine / genetics*
  • Tyrosine / metabolism


  • Anion Exchange Resins
  • Bacterial Proteins
  • Hemagglutinins
  • Lectins
  • Oligopeptides
  • Peptide Elongation Factor 2
  • Peptide Elongation Factors
  • Peptides
  • Phosphoproteins
  • Resins, Synthetic
  • hemagglutinin A, Porphyromonas gingivalis
  • Tyrosine
  • Mono Q
  • FLAG peptide
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 2
  • Leucine