1CVB: STRUCTURAL AND FUNCTIONAL IMPORTANCE OF A CONSERVED HYDROGEN BOND NETWORK IN HUMAN CARBONIC ANHYDRASE II

Citation:
Abstract
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-.
PDB ID: 1CVBDownload
MMDB ID: 55860
PDB Deposition Date: 1993/2/4
Updated in MMDB: 2017/12
Experimental Method:
x-ray diffraction
Resolution: 2.4  Å
Source Organism:
Similar Structures:
Biological Unit for 1CVB: monomeric; determined by author
Molecular Components in 1CVB
Label Count Molecule
Protein (1 molecule)
1
Carbonic Anhydrase II(Gene symbol: CA2)
Molecule annotation
Chemicals (2 molecules)
1
1
2
1
* Click molecule labels to explore molecular sequence information.

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