1cvb
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STRUCTURAL AND FUNCTIONAL IMPORTANCE OF A CONSERVED HYDROGEN BOND NETWORK IN HUMAN CARBONIC ANHYDRASE II
OverviewOverview
Amino acid substitutions at Thr199 of human carbonic anhydrase II (CAII), (Thr199-->Ser, Ala, Val, and Pro) were characterized to investigate the, importance of a conserved hydrogen bonding network. The three-dimensional, structures of azide-bound and sulfate-bound T199V CAIIs were determined by, x-ray crystallographic methods at 2.25 and 2.4 A, respectively (final, crystallographic R factors are 0.173 and 0.174, respectively). The CO2, hydrase activities of T199S and T199P variants suggest that the side chain, methyl and backbone amino functionalities stabilize the transition state, by approximately 0.4 and 0.8 kcal/mol, respectively. The side chain, hydroxyl group causes: stabilization of zinc-hydroxide relative to, zinc-water (pKa increases approximately 2 units); stabilization of the, transition state for bicarbonate dehydration relative to the CAII.HCO3-, complex (approximately 5 kcal/mol); and destabilization of the CAII.HCO3-, complex (approximately 0.8 kcal/mol). An inverse correlation between, log(kcatCO2/KM) and the pKa of zinc-water (r = 0.95, slope = -1) indicates, that the hydrogen bonding network stabilizes the chemical transition state, and zinc-hydroxide similarly. These data are consistent with the hydroxyl, group of Thr199 forming a hydrogen bond with the transition state and a, non-hydrogen-bonded van der Waals contact with CAII.HCO3-.
DiseaseDisease
Known disease associated with this structure: Osteopetrosis, autosomal recessive 3, with renal tubular acidosis OMIM:[611492]
About this StructureAbout this Structure
1CVB 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 and functional importance of a conserved hydrogen bond network in human carbonic anhydrase II., Krebs JF, Ippolito JA, Christianson DW, Fierke CA, J Biol Chem. 1993 Dec 25;268(36):27458-66. PMID:8262987
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