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Characterization of conditions required for X-Ray diffraction experiments with protein microcrystals
R Glaeser1, M Facciotti, P Walian
1Department of Molecular and Cell Biology, Lawrence Berkeley National Laboratory, University of California-Berkeley 94720, USA. rmglaeser@lbl.gov
Biophysical Journal
|May 29, 2000
Summary
Researchers quantified x-ray damage thresholds for frozen bacteriorhodopsin crystals, determining optimal exposure limits for high-resolution diffraction. This research provides guidelines for protein microcrystal analysis using X-ray diffraction.
Area of Science:
- Structural Biology
- Crystallography
- Biophysics
Background:
- Radiation damage is a critical factor limiting the resolution of X-ray diffraction data from protein microcrystals.
- Understanding X-ray exposure limits is essential for optimizing diffraction experiments on sensitive biological samples like bacteriorhodopsin.
Purpose of the Study:
- To quantify the X-ray exposure at which significant radiation damage occurs in frozen bacteriorhodopsin crystals.
- To establish practical guidelines for high-resolution X-ray diffraction experiments on protein microcrystals.
Main Methods:
- Quantification of X-ray damage thresholds using approximately 11-keV X-rays on frozen bacteriorhodopsin crystals.
- Analysis of sample heating effects at various X-ray flux densities.
- Determination of minimum crystal size requirements for collecting multiple high-resolution diffraction patterns.
Main Results:
- The maximum tolerable X-ray exposure for high-resolution diffraction is approximately 10(10) photons/microm(2).
- Significant sample heating is not expected below X-ray flux densities of 10(9) photons/s-microm(2).
- Crystals of approximately 10(11) unit cells can yield around 100 high-resolution diffraction patterns.
Conclusions:
- Established X-ray exposure limits and crystal size guidelines facilitate high-resolution diffraction from protein microcrystals.
- Reducing background scattering through improved microcollimation and using helium in cryo-streams can enhance data quality from small microcrystals.