Atomic insights into the mechanism of trace water influence on lipase catalysis in organic media

Lipase catalysis plays an important role in bioengineering and food science and is widely used in the organic solvent environment. The addition of trace water to organic media can significantly change lipase activity, and the reason is essential to understand. In this study, by combining experiments and molecular dynamics simulations, we studied solvent-free acidolysis of the tripalmitin (PPP) with different water contents and revealed the mechanism of the water effect on lipase activity from atomic insight. Enzyme activity experimentally exhibited an increasing but subsequently decreasing trend with the rise of water content. Through molecular dynamics (MD) simulations, we found that the reaction activity was affected by three aspects: lipase flexibility, substrate diffusion and substrate spatial distribution. Lipase flexibility, as the structural basis of catalytic activity, increased with water content. At lower water content, the diffusion ability of the substrate around the lipase was dominant. With water content increasing, water molecules on the protein surface gradually shielded hydrogen bonds (HBs) between the oleic acids (OA) and the lipase, which improved the diffusion ability of the substrate near the enzyme surface and thus beneficial to the reaction occurring. At higher water content, the spatial distribution dominated the reaction, where the thicker water layer on the lipase surface acted as a spatial barrier hindering the access of substrate OA to the enzyme and thus harmful to the reaction. Our work helps to provide guidance on controlling enzyme activities in organic solvent systems.