The crystal structure of carbonic anhydrase from @entity6368 has been solved to a resolution of 1.78 A by molecular replacement using @entity1 @entity7464 as a template. After refinement the R factor was 17.8% (Rfree=23.2%). There are two molecules per asymmetric unit (space group @entity3544 ), but they have essentially identical structures. The fold of the @entity6368 enzyme is very similar to that of @entity1 isozyme II; 192 residues, 74 of which are identical in the two enzymes, have equivalent positions in the three-dimensional structures. This corresponds to 85% of the entire polypeptide chain of the bacterial enzyme. The only two @entity462 residues in the bacterial enzyme, which has a periplasmic location in the cell, are connected by a @entity1520 bond. Most of the secondary structure elements present in @entity1 isozyme II are retained in @entity6368 carbonic anhydrase, but there are also differences, particularly in the few helical regions. Long deletions in the bacterial enzyme relative to @entity1 isozyme II have resulted in a considerable shortening of three surface loops. One of these deletions, corresponding to residues 128 to 139 in the @entity1 enzyme, leads to a widening of the entrance to the hydrophobic part of the active site cavity. Practically all the @entity535 residues in the active site of @entity1 isozyme II are conserved in the @entity6368 enzyme and have similar structural positions. However, the @entity8304 ring of a @entity3793 residue, which has been shown to function as a proton shuttle in the catalytic mechanism of the @entity1 enzyme, interacts with an extraneous entity, which has tentatively been identified as a 2- @entity6514 molecule from the crystallization medium. When this entity is removed by soaking the crystal in a different medium, the side-chain of His66 becomes quite mobile. The structure of a complex with the @entity11682 inhibitor, @entity3791 , has also been determined. Its position in the active site is very similar to that observed in @entity1 @entity7464 .

Crystal structure of carbonic anhydrase from @entity6368 and its complex with the inhibitor XXXX .

@entity1 :: ('9606', 'Species') :: ['human'] @entity6368 :: ('485', 'Species') :: ['Neisseria gonorrhoeae', 'N. gonorrhoeae'] @entity462 :: ('MESH:D003545', 'Chemical') :: ['cysteine'] @entity11682 :: ('CHEBI:35358', 'Chemical') :: ['sulfonamide'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity3793 :: ('CHEBI:27570', 'Chemical') :: ['histidine'] @entity3791 :: ('MESH:D000086', 'Chemical') :: ['acetazolamide'] @entity3544 :: ('644914', 'Gene') :: ['P21'] @entity7464 :: ('760', 'Gene') :: ['carbonic anhydrase II'] @entity8304 :: ('MESH:C029899', 'Chemical') :: ['imidazole'] @entity6514 :: ('MESH:D008623', 'Chemical') :: ['mercaptoethanol'] @entity1520 :: ('CHEBI:48343', 'Chemical') :: ['disulfide']
@entity3791 :: (MESH:D000086,Chemical) :: ['acetazolamide']
