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PDBsum entry 1cam

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Lyase(oxo-acid) PDB id
1cam
Jmol
Contents
Protein chain
258 a.a.
Ligands
BCT
Metals
_ZN
Waters ×214

References listed in PDB file
Key reference
Title Structural analysis of the zinc hydroxide-Thr-199-Glu-106 hydrogen-Bond network in human carbonic anhydrase ii.
Authors Y.Xue, A.Liljas, B.H.Jonsson, S.Lindskog.
Ref. Proteins, 1993, 17, 93.
PubMed id 7901850
Note: In the PDB file this reference is annotated as "TO BE PUBLISHED". The citation details given above were obtained from the PDBe's Unpublished References server.
Abstract
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.
PROCHECK
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