Atomic resolution studies of carbonic anhydrase II

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• Carbonic anhydrase is crucial for respiration and has been extensively studied.
• Numerous X-ray crystallographic structures of carbonic anhydrase and its inhibitor complexes exist.
• Atomic resolution structures provide detailed insights into enzyme function.

Purpose of the Study:

• To determine the structure of a sulfonamide-inhibitor complex of carbonic anhydrase at 0.9 A resolution.
• To compare this structure with other high-resolution carbonic anhydrase structures.
• To analyze structural similarity and variability in carbonic anhydrase crystal structures.

Main Methods:

• X-ray crystallography was used to determine the structure of the carbonic anhydrase-inhibitor complex.
• The structure was refined to 0.9 A resolution using anisotropic atomic displacement parameters.
• Comparison involved 13 other isomorphous carbonic anhydrase structures at atomic resolution.

Main Results:

• The determined structure is similar to other carbonic anhydrase complexes, with the inhibitor acting as a fourth ligand to the active-site zinc.
• Core protein structures superpose well, with minimal variation in zinc-protein and zinc-ligand bond lengths.
• Significant structural variability was observed on the protein surface, attributed to flexibility, disorder, environmental differences, or modeling approaches.

Conclusions:

• Carbonic anhydrase active sites are structurally conserved across different crystal structures.
• Protein surface regions exhibit considerable variability, even at atomic resolution.
• Caution is advised when interpreting protein surface structural details from individual X-ray structures, irrespective of resolution.