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Updated: Apr 25, 2026

Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
10:27

Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells

Published on: March 9, 2012

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Src promotes GTPase activity of Ras via tyrosine 32 phosphorylation

Severa Bunda1, Pardeep Heir2, Tharan Srikumar3

  • 1Departments of Laboratory Medicine and Pathobiology and Biochemistry, University of Toronto, Toronto, ON, Canada M5S1A8;

Proceedings of the National Academy of Sciences of the United States of America
|August 27, 2014
PubMed

Insights

The Src kinase phosphorylates Ras GTPase at Y32, modulating its activity. This phosphorylation reduces Ras binding to Raf and increases GTP hydrolysis, regulating the Ras signaling pathway.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Oncogenesis

Background:

  • Mutations in Ras GTPase pathways are common in human cancers and developmental syndromes.
  • The nonreceptor tyrosine kinase Src is known to promote Ras/Raf/MAP kinase (MAPK) signaling, crucial for cell functions.
  • A direct mechanistic link between Ras and Src has been previously unestablished.

Purpose of the Study:

  • To investigate the direct interaction and functional relationship between Ras GTPase and Src.
  • To elucidate the role of Src in modulating Ras activity and its downstream signaling.

Main Methods:

  • In vitro binding and phosphorylation assays using GTP- or GDP-loaded Ras.
  • In vivo studies to assess the impact of Ras phosphorylation on effector binding and GTPase activity.
  • Analysis of Ras-Y32 phosphorylation effects on binding affinities to Raf and GTPase-activating proteins (GAPs).

Main Results:

  • Src directly binds and phosphorylates GTP-loaded Ras at the conserved Y32 residue in the switch I region.
  • Ras-Y32 phosphorylation significantly reduces binding affinity to the downstream effector Raf.
  • Phosphorylation at Y32 enhances Ras binding to GTPase-activating proteins (GAPs), accelerating GTP hydrolysis.

Conclusions:

  • Ras-Y32 phosphorylation by Src acts as a critical regulatory mechanism for Ras GTPase activity.
  • This Src-dependent phosphorylation ensures unidirectionality in the Ras GTPase cycle by modulating effector interactions.
  • The findings establish a direct link between Src and Ras, highlighting a key regulatory node in cancer-related signaling pathways.

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