title: Experiments testing the abatement of radiation damage in D-xylose isomerase crystals with cryogenic helium.
abstract: Helium is a more efficient cryogen than nitrogen, and for macromolecular data collection at high-flux beamlines will deliver lower temperatures. An open-flow helium cryostat developed at the University of Toledo (the Pinkerton Device) has been used for macromolecular data collection. This device differs from standard commercial He cryostats by having a much narrower aperture providing a high velocity stream of He around the crystal that maximizes convective and conductive heat exchange between the crystal and the cryogen. This paper details a series of experiments conducted at the IMCA-CAT 17ID beamline using one crystal for each experimental condition to examine whether helium at 16 K provided better radiation-damage abatement compared with nitrogen at 100 K. These studies used matched high-quality crystals (0.94 A diffraction resolution) of D-xylose isomerase derived from the commercial material Gensweet SGI. Comparisons show that helium indeed abates the indicators of radiation damage, in this case resulting in longer crystal diffractive lifetimes. The overall trend suggests that crystals maintain order and that high-resolution data are less affected by increased radiation load when crystals are cooled with He rather than N(2). This is probably the result of a lower effective temperature at the crystal with concomitant reduction in free-radical diffusion. Other features, such as an apparent phase transition in macromolecular crystals at lower temperatures, require investigation to broaden the utility of He use.
authors.affiliation: University of Tennessee Oak Ridge Graduate School of Genome Science and Technology, PO Box 2009, Oak Ridge, TN 37831-8080, USA. blm@ornl.gov
authors.forename: B Leif
authors.initials: BL
authors.lastname: Hanson
authors.forename: Joel M
authors.initials: JM
authors.lastname: Harp
authors.forename: Kristin
authors.initials: K
authors.lastname: Kirschbaum
authors.forename: Constance A
authors.initials: CA
authors.lastname: Schall
authors.forename: Ken
authors.initials: K
authors.lastname: DeWitt
authors.forename: Andrew
authors.initials: A
authors.lastname: Howard
authors.forename: A Alan
authors.initials: AA
authors.lastname: Pinkerton
authors.forename: Gerard J
authors.initials: GJ
authors.lastname: Bunick
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000528:radiation effects*; D000818:Animals; D002415:Cats; D003080:Cold Temperature; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D006371:Helium; D006801:Humans; D008795:Metronidazole / Q000528:radiation effects; D008962:Models, Theoretical; D011832:Radiation Injuries / Q000209:etiology*; D012542:Scattering, Radiation; D014961:X-Ray Diffraction; D014994:Xylose / Q000528:radiation effects*
chemical_list: D008795:Metronidazole; D006371:Helium; D014994:Xylose; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase