view article
Figure 1
A likely catalytic mechanism for human carbonic anhydrase II. In the first step (a) the zinc water (WZn) releases a proton to His64 via W1 and W2. When carbon dioxide binds (b) it releases the two deep-water molecules. W1 disappears and is replaced by WI. His64 adopts the outward orientation to release the abstracted proton to bulk solvent. Then the WZn makes a nucleophilic attack on the carbon of the carbon dioxide to form bicarbonate (c). Three water molecules rapidly replace the bicarbonate and His64 returns to its inward orientation (a). Several additional water molecules are identified and participate in the dynamic water structure of the active site.

IUCrJ
Volume 5| Part 1| January 2018| Pages 4-5
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517018012