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The low Mr phosphotyrosine protein phosphatase behaves differently when phosphorylated at Tyr131 or Tyr132 by Src

M Bucciantini1, P Chiarugi, P Cirri

  • 1Department of Biochemical Sciences, University of Florence, Italy.

FEBS Letters
|August 19, 1999
PubMed

Insights

Low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) phosphorylation by Src kinase activates enzyme activity at Tyr131 and promotes Grb2 binding at Tyr132. This study reveals distinct functional outcomes of specific tyrosine residue phosphorylation in LMW-PTP signaling.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Signaling

Background:

  • Low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) is a key enzyme in cellular signaling pathways.
  • LMW-PTP is known to be phosphorylated by Src and Src-related kinases.
  • Tyrosine phosphorylation of LMW-PTP occurs in response to stimuli like platelet-derived growth factor (PDGF).

Purpose of the Study:

  • To investigate the specific effects of LMW-PTP phosphorylation at Tyr131 and Tyr132 residues by pp60Src.
  • To compare the phosphorylation efficacy of pp60Src and PDGF-receptor (PDGF-R) kinase on LMW-PTP.
  • To elucidate the functional consequences of phosphorylation at distinct tyrosine sites on LMW-PTP activity and interactions.

Main Methods:

  • In vitro phosphorylation assays using purified pp60Src and LMW-PTP.
  • Site-directed mutagenesis to create Tyr131 and Tyr132 phosphorylation site mutants of LMW-PTP.
  • Enzyme activity assays to measure specific activity changes.
  • Analysis of Grb2 protein recruitment to phosphorylated LMW-PTP.

Main Results:

  • pp60Src specifically phosphorylates LMW-PTP at Tyr131 and Tyr132 in vitro.
  • Phosphorylation at Tyr131 significantly increases LMW-PTP specific activity (approximately 25-fold).
  • Phosphorylation at Tyr132 facilitates the recruitment of Grb2 to LMW-PTP.

Conclusions:

  • Distinct tyrosine phosphorylation sites on LMW-PTP mediate different downstream signaling events.
  • Tyr131 phosphorylation enhances enzymatic function, while Tyr132 phosphorylation modulates protein-protein interactions.
  • These findings provide insights into the structure-function relationship of LMW-PTP regulation by Src family kinases.

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