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One-step evolution of a dimer from a monomeric protein
S M Green1, A G Gittis, A K Meeker
1Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Nature Structural Biology
|September 1, 1995
Summary
Altering staphylococcal nuclease by deleting six amino acids transforms it into a stable dimer. This structural change, involving swapped alpha-helices, creates a large protein-protein interface, offering insights into protein evolution.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Science
Background:
- Staphylococcal nuclease typically exists as a monomer.
- Understanding protein dimerization is crucial for various biological processes.
Purpose of the Study:
- To investigate how structural modifications affect protein quaternary structure.
- To explore the mechanism of stable dimer formation in proteins.
Main Methods:
- Site-directed mutagenesis to delete six amino acids in a surface loop.
- X-ray crystallography to determine the 3D structure of the resulting dimer.
- Analysis of protein-protein interfaces and binding affinities (Kd).
Main Results:
- Deletion resulted in a highly stable dimer (Kd < 1 x 10(-8)M).
- X-ray structure revealed a swapped carboxy-terminal alpha-helix forming a major interface (2900 A^2).
- A secondary interface (460 A^2) was also identified.
Conclusions:
- Spontaneous swapping of secondary structural elements can create large, stable protein interfaces.
- This mechanism may be significant in the evolution of oligomeric proteins.
- Structural plasticity enables novel protein-protein interactions.