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Refinement of triclinic hen egg-white lysozyme at atomic resolution
M A Walsh1, T R Schneider, L C Sieker
1European Molecular Biology Laboratory (EMBL), c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany. walsh@anl.gov
Acta Crystallographica. Section D, Biological Crystallography
|October 8, 1998
Summary
High-resolution X-ray diffraction studies of hen egg-white lysozyme at low and room temperatures reveal distinct conformational changes in amino acid side chains and water molecule arrangements, impacting protein structure dynamics.
Area of Science:
- Structural Biology
- Biophysics
- Crystallography
Background:
- Hen egg-white lysozyme is a well-studied enzyme.
- Understanding protein dynamics at different temperatures is crucial for comprehending biological function.
- High-resolution structural data provides insights into molecular interactions and conformational flexibility.
Purpose of the Study:
- To determine the high-resolution crystal structure of hen egg-white lysozyme at both low (120 K) and room temperatures.
- To compare the structural differences, including amino acid side-chain conformations and solvent molecule organization, between the two temperature conditions.
- To assess the significance of refining water molecule occupancies in protein crystallography.
Main Methods:
- Collected X-ray diffraction data from triclinic crystals of hen egg-white lysozyme at 120 K and room temperature to high resolution (0.925-0.950 Å) using synchrotron radiation.
- Refined the crystal structures using PROLSQ, ARP, and SHELXL programs.
- Analyzed and compared the refined structures, focusing on side-chain conformations, water molecules, and ions.
Main Results:
- The low-temperature structure (120 K) revealed multiple conformations for 24 amino acid side chains, 250 water molecules, six nitrate ions, and three acetate ions.
- The room-temperature structure showed multiple conformations for eight side chains, 139 water molecules, and six nitrate ions, with no acetate ions.
- Refinement of water molecule occupancies was found to be meaningful, as assessed by the free R factor.
Conclusions:
- Temperature significantly influences the conformational states of amino acid side chains and the organization of solvent molecules within the hen egg-white lysozyme crystal structure.
- High-resolution crystallographic data at different temperatures can reveal subtle yet important structural dynamics.
- The study highlights the importance of considering temperature effects and refining solvent occupancies for accurate protein structure determination.