1hcb
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ENZYME-SUBSTRATE INTERACTIONS: STRUCTURE OF HUMAN CARBONIC ANHYDRASE I COMPLEXED WITH BICARBONATE
OverviewOverview
The structure of HCAI-HCO3- complex has been refined with 10-1.6A X-ray, diffraction data to an R-value of 17.7%. The structure reveals monodentate, binding of the HCO3- anion at an apical tetrahedral position to the zinc, ion. The binding mode and interactions of HCO3- in HCAI differ from that, in HCAII. The activity linked H2O/OH- group in the free HCAI is replaced, by the hydroxyl group of the bicarbonate anion. This result rules out the, rearrangement of the bound HCO3- advocated earlier to explain the, microscopic reversibility of the catalysed reaction. From the geometry of, the H-bonds between Glu106-Thr199 pair and Glu117-His119 couple, the, glutamic acids are expected to be ionized and accept H-bonds from their, partners. The product-inhibiton by HCO3- anion is explained on the basis, of proton localization on His119 in the Glu117-His119 couple. These, results are consistent with the hypothesis that Glu117-His119 tunes the, ionicity of the Zn2+ and the binding strength of HCO3- anion. A pi, hydrogen bond is observed between a water and phenyl ring of the Tyr114, residue.
About this StructureAbout this Structure
1HCB is a Single protein structure of sequence from Homo sapiens with ZN and BCT as ligands. Active as Carbonate dehydratase, with EC number 4.2.1.1 Full crystallographic information is available from OCA.
ReferenceReference
Enzyme-substrate interactions. Structure of human carbonic anhydrase I complexed with bicarbonate., Kumar V, Kannan KK, J Mol Biol. 1994 Aug 12;241(2):226-32. PMID:8057362
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