Breaking hydrogen bond network enhances oxygenic photosynthesis of photosystem II

Protein hydration water plays a crucial role in maintaining protein structures and functions, yet it remains challenging to manipulate. In this study, we use photosystem II (PS II), a protein complex consisting of 25 membrane proteins, as a model to explore the regulation of protein functions by modifying the hydration water structure. Within PS II, two water molecules are transported from the bulk solution through water channels into the oxygen-evolving center (OEC), where they are oxidized into oxygen. However, the role of water—both in hydrating PS II proteins and in transporting water through channels to the OEC—has often been overlooked. By studying the effects of different ions, including structure-making ions (Na⁺) and breaking ions (K⁺), on photosynthesis performance, we revealed distinctive different catalytic effects induced by these ions. Molecular dynamics simulations and Terahertz spectroscopy demonstrated that K⁺ disrupts the hydrogen-bond network of hydration water, thereby facilitating water transportation to the O1 channel near the OEC, which in turn boosts oxygen evolution. In contrast, Na⁺ did not exhibit the same effect. These findings underscore the essential role of K⁺ in plant photosynthesis and reveal previously unrecognized mechanisms by which ions influence protein function through hydration water structure.