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Structural changes induced in p21Ras upon GAP-334 complexation as probed by ESEEM spectroscopy and molecular-dynamics
1Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138, USA.
Structure (London, England : 1993)
|February 24, 2001
Summary
The protein GAP regulates growth signaling by accelerating GTP hydrolysis. New studies show that GAP binding induces conformational changes in p21Ras, involving glycine residues crucial for this reaction.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- GTP hydrolysis by GTPase-activating protein (GAP) downregulates p21Ras growth signaling.
- p21Ras mutants are implicated in human cancers.
- A GAP arginine finger was proposed as key for GTP hydrolysis, but mutagenesis data suggests other factors are involved.
Purpose of the Study:
- To investigate the structural mechanisms by which GAP accelerates GTP hydrolysis by p21Ras.
- To elucidate the role of specific p21Ras residues in the GAP-mediated GTPase reaction.
Main Methods:
- Electron spin-echo envelope modulation (ESEEM) studies of GAP-334 complexed with GMPPNP bound p21.
- Molecular-dynamics simulations.
Main Results:
- GAP-334 binding to GTP-bound p21 induces a conformational change near the metal ion active site.
- This conformational change significantly reduces the distances between the metal ion and amide groups of p21 glycine residues 60 and 13.
Conclusions:
- The movement of Gly60 and Gly13 upon GAP-334 binding provides a physical basis for their known roles in the GAP-dependent GTPase reaction.
- Gly60 and Gly13 may directly participate in catalysis by stabilizing key reaction components.
- Gly60's amide proton may indirectly contribute to catalysis by stabilizing loop L4 and other catalytic residues.