X-RAY STUDIES ON CROSS-LINKED LYSOZYME CRYSTALS IN ACETONITRILE-WATERMIXTURE

Tetragonal crystals of hen egg white lysozyme were cross-linked and su bjected to X-ray diffraction study in acetonitrile-water media with di fferent acetonitrile concentrations. Crystals in neat acetonitrile did not scatter X-ray well. Structures of crystals in neat water, in 90% and 95% acetonitrile, and crystal back-soaked from acetonitrile to wat er, were determined to about 2 Angstrom resolution. For crystals in bo th 90% and 95% acetonitrile, only one protein-bond acetonitrile molecu le is found in the active site cleft, and its location and binding-pro tein mode is similar to the C subunit of polysaccharide. The alteratio n in conformation and hydrogen-bond pattern involving water as solvent causes the reduction of the protein's flexibility in organic media. T he back-soaked crystal regained its ordinary three-dimensional structu re in water. (C) 1998 Elsevier Science B.V. All rights reserved.