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Structural changes in a cryo-cooled protein crystal owing to radiation damage
1European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble CEDEX, France. wpb@esrf.fr
Summary
X-ray crystallography reveals that even cryo-cooled protein crystals suffer radiation damage, leading to structural changes like disulfide bond breakage. This damage limits the amount of data extractable from protein crystals, impacting structural studies.
Area of Science:
- Structural Biology
- Biophysics
- Crystallography
Background:
- Third-generation X-ray sources and cryo-cooling advance protein crystallography.
- Radiation damage remains a significant limitation, causing intensity loss and increased temperature factors.
Purpose of the Study:
- To investigate the structural consequences of X-ray radiation damage in cryo-cooled protein crystals.
- To analyze radiation-induced changes in myrosinase structure at different X-ray doses.
Main Methods:
- Exposure of myrosinase crystals to varying X-ray doses (approx. 20 x 10^15 photons mm^-2).
- Analysis of structural changes using Fourier difference maps and occupancy refinement.
- Detailed examination of specific residue modifications.
Main Results:
- Observed breakage of disulfide bonds and decarboxylation of aspartate/glutamate residues.
- Identified loss of hydroxyl groups from tyrosine and methylthio groups from methionine.
- Demonstrated variable susceptibility to radiation damage among similar chemical groups within the protein.
Conclusions:
- Radiation damage can compromise protein crystal structure model quality and interfere with data interpretation (e.g., ligand binding, MAD data).
- There is an intrinsic limit to data acquisition from protein crystals due to radiation-induced radiolysis.
- Understanding these damage mechanisms is crucial for optimizing X-ray crystallography experiments.