Determination of two structural forms of catalytic bridging ligand in zinc - Phosphotriesterase by molecular dynamics simulation and quantum chemical calculation

Although a three-dimensional X-ray crystal structure of zinc-substituted phosphotriesterase was recently reported, it is uncertain whether a critical bridging ligand in the active site is a water molecule or a hydroxide ion. The identity of this bridging ligand is theoretically determined by performing both molecular dynamics simulations and quantum mechanical calculations. All of the results obtained indicate that this critical ligand in the active site of the reported X-ray crystal structure is a hydroxide anion rather than a water molecule and allow us to propose a dynamic 'ping- pong' model in which both kinds of structures might exist.