Crystal structure of human erythrocyte carbonic anhydrase C: III. Molecular structure of the enzyme and of one enzyme-inhibitor complex at 5.5 Å resolution

Abstract

The structures of human carbonic anhydrase C and of the complex between the enzyme and the inhibitor acetoxymercurisulphanilamide have been determined by X-ray diffraction using four heavy-atom derivatives. The enzyme molecule is an ellipsoid with the approximate dimensions 40 Å × 45 Å × 55 Å. At the active site the molecule has a large cavity, at the bottom of which the zinc atom is bound. One part of the cavity is a narrow slit where the sulphonamide inhibitor attach and bind to the zinc. The distance between the zinc atom and the only SH-group of the enzyme is about 14 Å. The most likely polypeptide chain-folding and the helical content are discussed.