Demonstration of the Benefits of Cryogenic Helium for Macromolecular Data Collection (February 2000)

Researchers in the Macromolecular Crystallography Group of the Life Sciences Division, Oak Ridge National Laboratory, have teamed up with scientists in the Department of Chemistry, University of Toledo, and the Industrial Macromolecular Crystallography Association Collaborative Access Team ( IMCA-CAT) beamline, Advanced Photon Source, Argonne National Laboratory to demonstrate the benefits of cryogenic helium for macromolecular data collection. A major issue affecting the use of DOE’s third-generation synchrotron beamlines is the damage to macromolecular crystals caused by extreme high-intensity radiation exposure. Unacceptable radiation damage has been reported on numerous occasions at third-generation beamlines despite the application of standard cryocrystallography practices that use cryogenic nitrogen to eliminate radiation damage. An open flow helium cryostat developed at the University of Toledo was used at the APS IMCA beamline to test helium as a protective cryogen, and to compare data collected at helium temperature to that collected at nitrogen temperature. Data were collected on matched crystals of the nucleosome core particle (NCP), fumarylacetoacetate hydrolase (FAH), and the murine monoclonal antibody BV0401 using an Oxford Cryosystems Cryostream and the Toledo Helium Cryostat.

The initial experience of using an open flow helium cryostat for macromolecular data collection at a synchrotron has been very favorable. Crystal lifetime was enhanced by using helium as a cryogen. At the end of data collection with NCP, crystals cooled by nitrogen were blackened, crystals cooled by helium remained clear. In addition to reduced radiation damage at the third-generation synchrotron beamline, the data collected at cryogenic helium temperature (below 30 K) showed an improvement in resolution and a significant enhancement of the intensity for weak data. For BV0401 the resolution of the data increased from 1.60 Å to 1.48 Å and the statistical quality of the high-resolution data improved approximately three-fold. These results suggest that the use of cryogenic helium in an open flow configuration may solve the major problem of unacceptable radiation damage to macromolecular crystals at third-generation synchrotrons, while also providing increased diffraction resolution, statistically better data, lower temperature factors, and improved electron density maps for elucidating the structures of important biological molecules. (Funding: DOE-OBER, Contact: Gerry Bunick, 576-2685, bunickgj@ornl.gov)