Mutation of interfaces in domain-swapped human betaB2-crystallin
Myron A Smith1, Orval A Bateman, Rainer Jaenicke
1Department of Crystallography, Institute of Structural and Molecular Biology, Birkbeck College, University of London, London WC1E 7HX, United Kingdom.
Protein Science : a Publication of the Protein Society
|March 1, 2007
Summary
Eye lens betagamma-crystallins use domain swapping for dimerization, with sequence dictating this process. Mutations reveal the importance of specific interfaces for higher assembly and protein stability.
Area of Science:
- Structural biology
- Protein biochemistry
- Ophthalmology
Background:
- Betagamma-crystallins are essential structural proteins in the eye lens.
- They exhibit modular architecture with Greek key motifs forming symmetric domains.
- These proteins assemble into higher-order structures crucial for lens transparency.
Purpose of the Study:
- To investigate the structural basis of domain swapping in betaB2-crystallin.
- To understand the role of sequence, assembly conditions, and interface networks in betagamma-crystallin assembly.
- To explore how these proteins achieve high concentration and stability in the lens.
Main Methods:
- X-ray crystallography of recombinant human betaB2-crystallin and its mutants.
- Analysis of solution characteristics of designed mutants.
- Structural comparison of betaB1- and betaB2-crystallin assemblies.
Main Results:
- Domain swapping in betaB2-crystallin is sequence-dependent, not influenced by assembly conditions.
- Mutations targeting ion pair networks or proline residues did not prevent dimerization or reverse domain swapping.
- A charge-reversal mutation disrupted the conserved domain-pairing interface, altering solution behavior.
- The study elucidated the relationship between linker conformation, ion pair networks, and higher assembly.
Conclusions:
- The sequence of betaB2-crystallin is optimized for domain swapping, contributing to its dimeric form.
- Higher assembly of betagamma-crystallin domains utilizes symmetry to generate diversity while preventing aggregation.
- These properties are vital for proteins functioning at high concentrations over long periods in the eye lens.
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