A 7 µm mini-beam improves diffraction data from small or imperfect crystals of macromolecules
- Biosciences Division, Argonne National Laboratory, Argonne, IL 60439 (United States)
- Life Sciences Institute, Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109 (United States)
An X-ray mini-beam of 8 × 6 µm cross-section was used to collect diffraction data from protein microcrystals with volumes as small as 150–300 µm{sup 3}. The benefits of the mini-beam for experiments with small crystals and with large inhomogeneous crystals are investigated. A simple apparatus for achieving beam sizes in the range 5-10 µm on a synchrotron beamline was implemented in combination with a small 125 × 25 µm focus. The resulting beam had sufficient flux for crystallographic data collection from samples smaller than 10 × 10 × 10 µm. Sample data were collected representing three different scenarios: (i) a complete 2.0 Å data set from a single strongly diffracting microcrystal, (ii) a complete and redundant 1.94 Å data set obtained by merging data from six microcrystals and (iii) a complete 2.24 Å data set from a needle-shaped crystal with less than 12 × 10 µm cross-section and average diffracting power. The resulting data were of high quality, leading to well refined structures with good electron-density maps. The signal-to-noise ratios for data collected from small crystals with the mini-beam were significantly higher than for equivalent data collected from the same crystal with a 125 × 25 µm beam. Relative to this large beam, use of the mini-beam also resulted in lower refined crystal mosaicities. The mini-beam proved to be advantageous for inhomogeneous large crystals, where better ordered regions could be selected by the smaller beam.
- OSTI ID:
- 22347996
- Journal Information:
- Acta Crystallographica. Section D: Biological Crystallography, Journal Name: Acta Crystallographica. Section D: Biological Crystallography Journal Issue: Pt 4 Vol. 64; ISSN ABCRE6; ISSN 0907-4449
- Country of Publication:
- Denmark
- Language:
- English
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