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Identification of tyrosine phosphorylation sites in human Gab-1 protein by EGF receptor kinase in vitro

S Lehr1, J Kotzka, A Herkner

  • 1Klinik II und Poliklinik für Innere Medizin am Zentrum für Molekulare Medizin Köln, Institut für Biochemie der Universit at zu Köln, Germany.

Biochemistry
|January 16, 1999
PubMed

Insights

Grb2-associated binder-1 (Gab-1) is a docking protein phosphorylated by the epidermal growth factor receptor (EGFR). The primary phosphorylation site, Y657, mediates specific binding to the tyrosine phosphatase Syp (PTP1D).

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Biochemistry

Background:

  • Grb2-associated binder-1 (Gab-1) is a key docking protein involved in cellular growth, transformation, and apoptosis.
  • Gab-1 functions downstream of receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR).
  • Understanding Gab-1 phosphorylation by EGFR is crucial for elucidating signaling pathways in glioblastoma.

Purpose of the Study:

  • To characterize the in vitro phosphorylation of recombinant human Gab-1 (hGab-1) by EGFR.
  • To identify specific EGFR phosphorylation sites on hGab-1.
  • To investigate the functional consequence of hGab-1 phosphorylation, particularly regarding Syp binding.

Main Methods:

  • Expression of full-length and domain-specific hGab-1 using the pGEX system.
  • Kinetic analysis of hGab-1 phosphorylation by purified EGFR and recombinant EGFR kinase domain.
  • Identification of phosphorylation sites using Edman degradation and mass spectrometry; GST-pull down assays for protein-protein interactions.

Main Results:

  • hGab-1 exhibits high affinity for EGFR kinase domain (KM = 2.7 microM).
  • EGFR phosphorylates hGab-1 at eight tyrosine residues, with Y657 being the predominant site (50% of radioactivity).
  • Phosphorylated hGab-1 specifically binds to Syp (PTP1D) via Y657, and this interaction is abolished by Y657F mutation.

Conclusions:

  • hGab-1 is a high-affinity substrate for EGFR.
  • Tyrosine 657 is the major phosphorylation site on hGab-1 by EGFR and serves as a specific binding site for Syp.
  • This interaction highlights a novel regulatory mechanism in EGFR signaling pathways.

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