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Why protein crystals favour some space-groups over others
1Department of Biomathematics, University of California, Los Angeles 90095-1766, USA.
Nature Structural Biology
|December 1, 1995
Summary
Protein crystallization space groups are non-uniformly distributed. An entropic model explains this, showing favored groups allow more molecular freedom, aiding crystallization of water-soluble and membrane proteins.
Area of Science:
- Biophysics
- Crystallography
- Structural Biology
Background:
- The non-uniform distribution of space-group symmetries in protein crystallography is a long-standing puzzle.
- Molecular close-packing explains this phenomenon in small organic compounds but not for proteins.
Purpose of the Study:
- To investigate the underlying principles governing the non-uniform occurrence of space-group symmetries in protein crystals.
- To propose a new model explaining the observed frequencies of space groups in protein crystallization.
Main Methods:
- Analysis of existing crystallographic data on space-group frequencies for 2D and 3D protein crystals.
- Development and application of an entropic model based on molecular degrees of freedom and connectivity requirements.
Main Results:
- The observed frequencies of space groups in protein crystals are not adequately explained by molecular close-packing.
- An entropic model successfully predicts the non-uniform distribution of space-group symmetries.
- Favored space groups are those that impose fewer restrictions on molecular arrangements, allowing greater rigid-body freedom.
Conclusions:
- The entropic model, emphasizing molecular freedom and connectivity, provides a robust explanation for space-group distribution in protein crystallization.
- The nucleation event plays a critical role in determining crystal symmetry.
- The findings offer insights for optimizing crystallization strategies for both water-soluble and membrane proteins.