Modeling the structure and proton transfer pathways of the mutant His-107-Tyr of human carbonic anhydrase II.

We present molecular modeling of the structure and possible proton transfer pathways from the surface of the protein to the zinc-bound water molecule in the active site of the mutant His-107-Tyr of human carbonic anhydrase II (HCAII). No high-resolution structure or crystal structure is available till now for this particular mutant due to its lack of stability at physiological temperature. Our analysis utilizes as starting point a series of structures derived from high-resolution crystal structure of the wild type protein. While many of the structures investigated do not reveal a complete path between the zinc bound water and His-64, several others do indicate the presence of a transient connection even when His-64 is present in its outward conformation. Mutation at the residue 107 also reveals the formation of a new path into the active site. Competing contributions from His-64 sidechain rotation from its outward conformation are also evaluated in terms of optimal path analysis. No indication of a lower catalytic efficiency of the mutant is evident from our results under the condition of thermal stability of the mutant.