Crystal Structure of a Zinc-Activated Variant of Human Carbonic Anhydrase I, CA I Michigan 1: Evidence for a Second Zinc Binding Site Involving Arginine Coordination

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• 作者：Marta Ferraroni ; Silvia Tilli ; Fabrizio Briganti ; W. Richard Chegwidden ; Claudiu T. Supuran ; Karin E Wiebauer ; Richard E. Tashian ; and Andrea Scozzafava
• 刊名：Biochemistry
• 出版年：2002
• 出版时间：May 21, 2002
• 年：2002
• 卷：41
• 期：20
• 页码：6237 - 6244
• 全文大小：288K
• 年卷期：v.41,no.20(May 21, 2002)
• ISSN：1520-4995

文摘

The human genetic variant carbonic anhydrase I (CA I) Michigan 1 results from a singlepoint mutation that changes His 67 to Arg in a critical region of the active site. This variant of the zincmetalloenzyme appears to be unique in that it possesses an esterase activity that is specifically enhancedby added free zinc ions. We have determined the three-dimensional structure of human CA I Michigan1 by X-ray crystallography to a resolution of 2.6 Å. In the absence of added zinc ions, the mutated residue,Arg 67, points out of the active site, hydrogen bonding with the carboxylate of Asn 69. This contrastswith the orientation of His 67, in the native isozyme, which points into the active site. The orientationsof His 94, His 96, and His 119, that coordinate the catalytic zinc ion, and of the catalytically critical Thr199-Glu 106 hydrogen bonding system, are largely unchanged in the mutant. The structure of an enzymeadduct with a second zinc bound was determined to a resolution of 2.0 Å. The second zinc ion is coordinatedto His 64, His 200, and Arg 67. This arginine residue reverses its orientation on zinc binding and turnsinto the active site. The residues at these three positions have been implicated in determining the specifickinetic properties of native CA I. This is, to our knowledge, the first example of a zinc ion coordinatingwith an arginine residue in a Zn(II) enzyme.