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 ph osphotriesterase 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 perform ing both molecular dynamics simulations and quantum mechanical calculations . All of the results obtained indicate that this critical ligand in the act ive site of the reported X-ray crystal structure is a hydroxide anion rathe r than a water molecule and allow us to propose a dynamic "ping-pong" model in which both kinds of structures might exist.