Macromolecular data collection with cryogenic helium

We have previously reported on the use of an open flow helium cryostat in m acromolecular crystallographic data collection. This device, developed at t he 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 a t N-2 temperature. Data were collected on matched crystals of the nucleosom e core particle (NCP), fumarylacetoacetate hydrolase (FAH), and the murine monoclonal antibody BV0401 (BV), and other crystals using an Oxford Cryosys tems Cryostream and the Toledo Helium Cryostat. In these experiments, cryst al lifetime was enhanced by using He as a cryogen. At the end of data colle ction with NCP, crystals cooled by N-2 were blackened; crystals cooled by H e 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 impr ovement is best illustrated in the diffraction data from BY. These data sho wed an improvement in resolution (1.75-1.48 Angstrom) with a significant en hancement of the intensity for weak data. Data from the NCP showed a simila r enhancement in intensity. However, some diffraction data exhibited split reflections at He temperature rendering processing of the data more problem atic. One possible explanation for these results is a phase change occurrin g between 100 K and the 30 K of the helium cold stream. Planned work will c haracterize this phenomenon and extend the experiments to other crystal sys tems. (C) 2001 Elsevier Science B.V. All rights reserved.