Lindahl M, Svensson L A, Liljas A
Department of Molecular Biophysics, University of Lund, Sweden.
Proteins. 1993 Feb;15(2):177-82. doi: 10.1002/prot.340150207.
Carbonic anhydrase is inhibited by the "metal poison" cyanide. Several spectroscopic investigations of carbonic anhydrase where the natural zinc ion has been replaced by cobalt have further strengthened the view that cyanide and cyanate bind directly to the metal. We have determined the structure of human carbonic anhydrase II inhibited by cyanide and cyanate, respectively, by X-ray crystallography. It is shown that the inhibitors replace a molecule of water, which forms a hydrogen bond to the peptide nitrogen of Thr-199 in the native structure. The coordination of the zinc ion is hereby left unaltered compared to the native crystal structure, so that the zinc coordinates three histidines and one molecule of water or hydroxyl ion in a tetrahedral fashion. The binding site of the two inhibitors is identical to what earlier has been suggested to be the position of the substrate (CO2) when attacked by the zinc bound hydroxyl ion. The peptide chain undergoes no significant alterations upon binding of either inhibitor.
碳酸酐酶被“金属毒物”氰化物所抑制。对天然锌离子被钴取代后的碳酸酐酶进行的多项光谱研究进一步强化了这样一种观点，即氰化物和氰酸盐直接与金属结合。我们通过X射线晶体学分别测定了被氰化物和氰酸盐抑制的人碳酸酐酶II的结构。结果表明，抑制剂取代了一个水分子，该水分子在天然结构中与苏氨酸-199的肽氮形成氢键。与天然晶体结构相比，锌离子的配位在此未发生改变，因此锌以四面体方式配位三个组氨酸和一个水分子或氢氧根离子。这两种抑制剂的结合位点与之前所认为的当被锌结合的氢氧根离子攻击时底物（二氧化碳）的位置相同。在结合任何一种抑制剂后，肽链都没有发生显著变化。
