1cah
From Proteopedia
STRUCTURE OF COBALT CARBONIC ANHYDRASE COMPLEXED WITH BICARBONATE
Overview
The three-dimensional structure of a complex between catalytically active cobalt(II) substituted human carbonic anhydrase II and its substrate bicarbonate was determined by X-ray crystallography (1.9 A). One water molecule and two bicarbonate oxygen atoms are found at distances between 2.3 and 2.5 A from the cobalt ion in addition to the three histidyl ligands contributed by the peptide chain. The tetrahedral geometry around the metal ion in the native enzyme with a single water molecule 2.0 A from the metal is therefore lost. The geometry is difficult to classify but might best be described as distorted octahedral. The structure is suggested to represent a water-bicarbonate exchange state relevant also for native carbonic anhydrase, where the two unprotonized oxygen atoms of the substrate are bound in a carboxylate binding site and the hydroxyl group is free to move closer to the metal thereby replacing the metal-bound water molecule. A reaction mechanism based on crystallographically determined enzyme-ligand complexes is represented.
About this Structure
1CAH is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.
Reference
Structure of cobalt carbonic anhydrase complexed with bicarbonate., Hakansson K, Wehnert A, J Mol Biol. 1992 Dec 20;228(4):1212-8. PMID:1474587 Page seeded by OCA on Fri May 2 12:31:28 2008
