Water migration through enzyme tunnels is sensitive to choice of explicit water model

Understanding the utilization of tunnels and water transport within enzymes is crucial for the catalytic function of enzymes, as water molecules can stabilize bound substrates and help with unbinding processes of products and inhibitors. Since the choice of water models for molecular dynamics simulations was shown to determine the accuracy of various calculated properties of the bulk solvent and solvated proteins, we have investigated if and to what extent the water transport through the enzyme tunnels depends on the selection of the water model. Here, we have focused on simulating enzymes with various well-defined tunnel geometries. In a systematic investigation using haloalkane dehalogenase as a model system, we focused on the well-established TIP3P, OPC, and TIP4P-Ew water models to explore their impact on using tunnels for water molecules transport. The TIP3P water model showed significantly faster migration, resulting in the transport of approximately 2.5 times more water molecules in comparison to OPC and 2.0 times greater than the TIP4P-Ew. The increase in migration of TIP3P water molecules was mainly due to faster transit times, and in the case of narrower tunnels, greater concurrent transport was evident as well. We have observed similar behavior in two different enzymes with buried active sites and different tunnel network topologies, indicating that our findings are likely not restricted to a particular enzyme family. Our study emphasizes the critical importance of water models in comprehending the use of enzyme tunnels for small molecule transport. Given the significant role of water availability in various stages of the catalytic cycle and solvation of substrates, products, and drugs, choosing an appropriate water model might be crucial for accurate simulations of complex enzymatic reactions, rational enzyme design, and predicting drug residence times.