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Structural basis for specificity switching of the Src SH2 domain.
M S Kimber1, J Nachman, A M Cunningham
1Department of Molecular and Medical Genetics, University of Toronto, Ontario, Canada.
Molecular Cell
|July 27, 2000
Summary
Single amino acid changes in Src SH2 domains rapidly alter their specificity, mimicking other domains like Grb2. This structural shift reveals how new signaling pathways can evolve through subtle protein modifications.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Src SH2 domains recognize phosphopeptides with specific sequences.
- The ThrEF1 residue in Src SH2 is crucial for binding Ile at the pY+3 position in an extended conformation.
Purpose of the Study:
- To elucidate the structural mechanism by which a single amino acid substitution in the Src SH2 domain switches its phosphopeptide binding specificity.
- To investigate how this mutation mimics the binding mode of the Grb2 SH2 domain.
Main Methods:
- Site-directed mutagenesis of the Src SH2 domain (ThrEF1 to Tryptophan).
- X-ray crystallography to determine the structure of the mutant Src SH2 domain bound to phosphopeptides.
- Structural comparison between the native Src SH2, mutant Src SH2, and native Grb2 SH2 domains.
Main Results:
- The Src ThrEF1Trp mutant binds pYVNV phosphopeptides in a beta turn conformation.
- The mutation occludes the original pTyr+3 binding pocket and creates new interactions for Asn at the pY+2 position.
- The binding mode of the mutant Src SH2 domain closely resembles that of the Grb2 SH2 domain.
Conclusions:
- Single amino acid substitutions can rapidly and drastically alter SH2 domain specificity.
- This provides a structural basis for the evolution of novel SH2 domain functions and potentially new signaling pathways.
- The study highlights the plasticity of protein-ligand interactions in signal transduction.