title: A 7μm mini-beam improves diffraction data from small or imperfect crystals of macromolecules.
abstract: 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 x 25 μm focus. The resulting beam had sufficient flux for crystallographic data collection from samples smaller than 10 x 10 x 10 μm. Sample data were collected representing three different scenarios: (i) a complete 2.0 data set from a single strongly diffracting microcrystal, (ii) a complete and redundant 1.94 A data set obtained by merging data from six microcrystals and (iii) a complete 2.24 A data set from a needle-shaped crystal with less than 12 x 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 x 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.
authors.affiliation: Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA. rsanishvili@anl.gov
authors.forename: Ruslan
authors.initials: R
authors.lastname: Sanishvili
authors.forename: Venugopalan
authors.initials: V
authors.lastname: Nagarajan
authors.forename: Derek
authors.initials: D
authors.lastname: Yoder
authors.forename: Michael
authors.initials: M
authors.lastname: Becker
authors.forename: Shenglan
authors.initials: S
authors.lastname: Xu
authors.forename: Stephen
authors.initials: S
authors.lastname: Corcoran
authors.forename: David L
authors.initials: DL
authors.lastname: Akey
authors.forename: Janet L
authors.initials: JL
authors.lastname: Smith
authors.forename: Robert F
authors.initials: RF
authors.lastname: Fischetti
mesh_terms: D003460:Crystallization; D003625:Data Collection; D003627:Data Interpretation, Statistical; D046911:Macromolecular Substances / Q000737:chemistry*; D008958:Models, Molecular; D014961:X-Ray Diffraction / Q000295:instrumentation*
chemical_list: D046911:Macromolecular Substances