Macromolecular data collection with cryogenic helium

We have previously reported on the use of an open flow helium cryostat in macromolecular crystallographic data collection. This device, developed at the University of Toledo, was used at the APS IMCA beamline to test He as a cryogen and to compare data collected at He temperature to that collected at N-2 temperature. Data were collected on matched crystals of the nucleosome core particle (NCP), fumarylacetoacetate hydrolase (FAH), and the murine monoclonal antibody BV0401 (BV), and other crystals using an Oxford Cryosystems Cryostream and the Toledo Helium Cryostat. In these experiments, crystal lifetime was enhanced by using He as a cryogen. At the end of data collection with NCP, crystals cooled by N-2 were blackened; crystals cooled by He remained clear. A crystal of Mcg light chain dimer (Mcg) had undiminished diffraction in He after 90 min of exposure in the same position. Data improvement is best illustrated in the diffraction data from BY. These data showed an improvement in resolution (1.75-1.48 Angstrom) with a significant enhancement of the intensity for weak data. Data from the NCP showed a similar enhancement in intensity. However, some diffraction data exhibited split reflections at He temperature rendering processing of the data more problematic. One possible explanation for these results is a phase change occurring between 100 K and the 30 K of the helium cold stream. Planned work will characterize this phenomenon and extend the experiments to other crystal systems. (C) 2001 Elsevier Science B.V. All rights reserved.