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Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
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Site-specific monoubiquitination activates Ras by impeding GTPase-activating protein function

Rachael Baker1, Steven M Lewis, Atsuo T Sasaki

  • 1Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.

Nature Structural & Molecular Biology
|November 27, 2012
PubMed

Insights

Monoubiquitination activates Ras proteins, crucial for cell growth, by blocking their inactivation. This discovery reveals a new pathway for persistent Ras signaling, independent of mutations, potentially driving cancer.

Area of Science:

  • Molecular biology
  • Cell signaling
  • Biochemistry

Background:

  • Ras GTPases are key regulators of cell growth and differentiation, often dysregulated in cancer.
  • Oncogenic mutations lead to persistent Ras signaling, promoting tumor development.
  • Emerging evidence suggests Ras monoubiquitination is a mechanism for Ras activation.

Purpose of the Study:

  • To elucidate the functional mechanism of human Ras activation by monoubiquitination.
  • To investigate how monoubiquitination affects Ras interaction with regulatory proteins.
  • To understand the implications of Ras monoubiquitination in signaling and disease.

Main Methods:

  • Chemical ubiquitination of purified human Ras protein.
  • Nuclear Magnetic Resonance (NMR) spectroscopy to analyze structural changes.
  • Computational modeling to predict protein interactions.
  • Biochemical assays to measure GTP binding, hydrolysis, and effector/inhibitor interactions.

Main Results:

  • Monoubiquitination minimally impacts Ras binding to guanine nucleotides, GTP hydrolysis, and exchange factor activation.
  • Monoubiquitination significantly impairs Ras interaction with GTPase-activating proteins (GAPs) in a site-specific manner.
  • This impairment leads to sustained Ras activity, mimicking oncogenic signaling.

Conclusions:

  • Ras monoubiquitination represents a novel mechanism for activating Ras signaling.
  • This activation pathway can persist independently of receptor stimulation or oncogenic mutations.
  • Understanding this mechanism offers new insights into cancer development and potential therapeutic targets.

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