1cak
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STRUCTURAL ANALYSIS OF THE ZINC HYDROXIDE-THR 199-GLU 106 HYDROGEN BONDING NETWORK IN HUMAN CARBONIC ANHYDRASE II
OverviewOverview
The significance of the zinc hydroxide-Thr-199-Glu-106 hydrogen-bond, network in the active site of human carbonic anhydrase II has been, examined by X-ray crystallographic analyses of site-specific mutants., Mutants with Ala-199 and Ala-106 or Gln-106 have low catalytic activities, while a mutant with Asp-106 has almost full CO2 hydration activity. The, structures of these four mutants, as well as that of the bicarbonate, complex of the mutant with Ala-199, have been determined at 1.7 to 2.2 A, resolution. Removal of the gamma atoms of residue 199 leads to a distorted, tetrahedral geometry at the zinc ion, and a catalytically important, zinc-bound water molecule has moved towards Glu-106. In the bicarbonate, complex of the mutant with Ala-199 one oxygen atom from bicarbonate binds, to zinc without displacing this water molecule. Tetrahedral coordination, geometries are retained in the mutants at position 106. The mutants with, Ala-106 and Gln-106 have a zinc-bound sulfate ion, whereas this sulfate, site is only partially occupied in the mutant with Asp-106. The, hydrogen-bond network seems to be "reversed" in the mutants with Ala-106, and Gln-106. The network is preserved as in native enzyme in the mutant, with Asp-106 but the side chain of Asp-106 is more extended than that of, Glu-106 in the native enzyme. These results illustrate the importance of, Glu-106 and Thr-199 for controlling the precise coordination geometry of, the zinc ion and its ligand preferences which results in an optimal, orientation of a zinc-bound hydroxide ion for an attack on the CO2, substrate.
DiseaseDisease
Known disease associated with this structure: Osteopetrosis, autosomal recessive 3, with renal tubular acidosis OMIM:[611492]
About this StructureAbout this Structure
1CAK is a Single protein structure of sequence from Homo sapiens with ZN and SO4 as ligands. Active as Carbonate dehydratase, with EC number 4.2.1.1 Full crystallographic information is available from OCA.
ReferenceReference
Structural analysis of the zinc hydroxide-Thr-199-Glu-106 hydrogen-bond network in human carbonic anhydrase II., Xue Y, Liljas A, Jonsson BH, Lindskog S, Proteins. 1993 Sep;17(1):93-106. PMID:7901850
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