1Z97: Human Carbonic Anhydrase Iii: Structural And Kinetic Study Of Catalysis And Proton Transfer

The residue phenylalanine 198 (Phe 198) is a prominent cause of the lower activity of human carbonic anhydrase III (HCA III) compared with HCA II and other isozymes which have leucine at this site. We report the crystal structures of HCA III and the site-directed mutant F198L HCA III, both at 2.1 A resolution, and the enhancement of catalytic activity by exogenous proton donors containing imidazole rings. Both enzymes had a hexahistidine extension at the carboxy-terminal end, used to aid in purification, that was ordered in the crystal structures bound in the active site cavity of an adjacent symmetry-related enzyme. This observation allowed us to comment on a number of possible binding sites for imidazole and derivatives as exogenous proton donors/acceptors in catalysis by HCA III. Kinetic and structural evidence indicates that the phenyl side chain of Phe 198 in HCA III, about 5 A from the zinc, is a steric constriction in the active site, may cause altered interactions at the zinc-bound solvent, and is a binding site for the activation of catalysis by histidylhistidine. This suggests that sites of activation of the proton-transfer pathway in carbonic anhydrase are closer to the zinc than considered in previous studies.
PDB ID: 1Z97Download
MMDB ID: 34710
PDB Deposition Date: 2005/3/31
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 2.1  Å
Source Organism:
Similar Structures:
Biological Unit for 1Z97: monomeric; determined by author
Molecular Components in 1Z97
Label Count Molecule
Protein (1 molecule)
Carbonic Anhydrase III(Gene symbol: CA3)
Molecule annotation
Chemical (1 molecule)
* Click molecule labels to explore molecular sequence information.

Citing MMDB