title: Refined structure of human carbonic anhydrase II at 2.0 A resolution.
abstract: The structure of human erythrocytic carbonic anhydrase II has been refined by constrained and restrained structure-factor least-squares refinement at 2.0 A resolution. The conventional crystallographic R value is 17.3%. Of 167 solvent molecules associated with the protein, four are buried and stabilize secondary structure elements. The zinc ion is ligated to three histidyl residues and one water molecule in a nearly tetrahedral geometry. In addition to the zinc-bound water, seven more water molecules are identified in the active site. Assuming that Glu-106 is deprotonated at pH 8.5, some of the hydrogen bond donor-acceptor relations in the active site can be assigned and are described here in detail. The O gamma 1 atom of Thr-199 donates its proton to the O epsilon 1 atom of Glu-106 and can function as a hydrogen bond acceptor only in additional hydrogen bonds.
authors.affiliation: Department of Molecular Biology, Biomedical Center, Uppsala, Sweden.
authors.forename: A E
authors.initials: AE
authors.lastname: Eriksson
authors.forename: T A
authors.initials: TA
authors.lastname: Jones
authors.forename: A
authors.initials: A
authors.lastname: Liljas
mesh_terms: D001665:Binding Sites; D002256:Carbonic Anhydrases; D004912:Erythrocytes / Q000201:enzymology; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011487:Protein Conformation; D012984:Software; D015032:Zinc
chemical_list: D002256:Carbonic Anhydrases; D015032:Zinc