X-ray crystal structure of cross-linked subtilisin Carlsberg in water vs. acetonitrile

The crystal structure of subtilisin Carlsberg lightly cross-linked with glutaraldehyde was solved in aqueous solution by X-ray crystallography at 2.3 A resolution. It was found to be virtually identical to the recently determined (Fitzpatrick, P.A., Steinmetz, A.C.U., Ringe, D.A. & Klibanov, A.M. (1993) Proc. Natl. Acad. Sci. USA 90, 8653) structure of the cross-linked enzyme in anhydrous acetonitrile. The latter structure was found to be significantly more rigid than in water, as reflected by their average B factors. The numbers of subtilisin-bound water molecules in the two structures are similar (114 and 99 in water and in acetonitrile, respectively), but the locations of some half of these bound waters are distinct.