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Comparison of X-Ray Crystal Structures of an Acyl-Enzyme Intermediate of Subtilisin Carlsberg Formed in Anhydrous Acetonitrile and in Water
Jennifer L. Schmitke, Lawrence J. Stern and Alexander M. Klibanov
Proceedings of the National Academy of Sciences of the United States of America
Vol. 95, No. 22 (Oct. 27, 1998), pp. 12918-12923
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/46169
Page Count: 6
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The x-ray crystal structures of trans-cinnamoyl-subtilisin, an acyl-enzyme covalent intermediate of the serine protease subtilisin Carlsberg, have been determined to 2.2- angstrom resolution in anhydrous acetonitrile and in water. The cinnamoyl-subtilisin structures are virtually identical in the two solvents. In addition, their enzyme portions are nearly indistinguishable from previously determined structures of the free enzyme in acetonitrile and in water; thus, acylation in either aqueous or nonaqueous solvent causes no appreciable conformational changes. However, the locations of bound solvent molecules in the active site of the acyl- and free enzyme forms in acetonitrile and in water are distinct. Such differences in the active site solvation may contribute to the observed variations in enzymatic activities. On prolonged exposure to organic solvent or removal of interstitial solvent from the crystal lattice, the channels within enzyme crystals are shown to collapse, leading to a drop in the number of active sites accessible to the substrate. The mechanistic and preparative implications of our findings for enzymatic catalysis in organic solvents are discussed.
Proceedings of the National Academy of Sciences of the United States of America © 1998 National Academy of Sciences