Neutron Structure of Human Carbonic Anhydrase II: Implications for Proton Transfer
Citations Over TimeTop 10% of 2009 papers
Abstract
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-D exchange 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 A resolution reveals several interesting active site features: (1) the Zn-bound solvent appearing to be predominantly a D(2)O 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.
Related Papers
- The acceleration of pH volume changes in human red cells by bicarbonate and the role of carbonic anhydrase.(1994)
- → Carbonic Anhydrase and the Maintenance of Intraocular Jension(1955)41 cited
- → The detection and localization of carbonic anhydrase in the rabbit cornea(1973)16 cited
- Evidence for voltage regulation of carbonic anhydrase-independent acidification in turtle bladder.(1985)
- → Carbonic Anhydrase Activity Assay v1(2017)