期刊
BIOCHEMISTRY
卷 49, 期 3, 页码 415-421出版社
AMER CHEMICAL SOC
DOI: 10.1021/bi901995n
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资金
- Office of Biological and Environmental Research of the Department of Energy
- National Institute or General Medical Sciences [IR01GM071939-01]
- LDRD [20080789PRD3]
- National Institutes of Health [GM25154]
- Thomas Maren Foundation
Human carbonic anhydrase II (HCA II) catalyzes the reversible hydration of carbon dioxide to form bicarbonate and a proton. Despite many high-resolution X-ray crystal structures, mutagenesis, and kinetic data, the structural details of the active site, especially the proton transfer pathway,are unclear. A large HCA II crystal was prepared at pH 9.0 and Subjected to vapor H-Dexchange to replace labile hydrogens with deuteriums. Neutron diffraction studies were conducted at the Protein Crystallography Station at Los Alamos National Laboratory. The structure to 2.0 angstrom resolution reveals several interesting active site features: (1) the Zn-bound solvent appearing to be predominantly a D2O molecule, (2) the orientation and hydrogen bonding pattern of solvent molecules in the active site cavity, (3) the side chain of His64 being unprotonated (neutral) and predominantly in an inward conformation pointing toward the zinc, and (4) the phenolic side chain of Tyr7 appearing to be Unprotonated. The implications of these details are discussed, and a proposed mechanism for proton transfer is presented.
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