Use of an open-flow helium cryostat for macromolecular cryocrystallography

A helium cryostat developed at the University of Toledo has recently been d escribed by Hardie, Kirschbaum, Martin & Pinkerton [J. Appl. Cryst. (1998), 31, 815-817]. This helium cooling system has now been tested on macromolec ules, using crystals of chicken egg lysozyme and sperm whale myoglobin. Pha se changes in terbium vanadate crystals indicate that temperatures delivere d by the cryostat were less than 33 K. Unit-cell contraction in the protein crystals is consistent with the previously reported He data. Large crystal s approaching suitability for neutron diffraction studies were successfully flash-cooled and a large crystal of lysozyme was rescued for data collecti on after undergoing a cycle of macromolecular crystal annealing (MCA) follo wing poor hash-cooling. Comparison of diffraction data from sperm whale myo globin crystals collected in both He and N-2 showed a 23% lower overall B f actor for the He data. The results of these studies show that this device m ight be an especially useful adjunct both for neutron diffraction studies a nd at high-intensity synchrotron X-ray sources, in addition to its use in t he standard macromolecular crystallography laboratory.