Necessity of structural rearrangements for O-O bond formation between O5 and W2 in photosystem II

Numerous aspects of the water oxidation mechanism in photosystem II have not been fully elucidated, especially the O-O bond formation pathway. However, a body of experimental evidences have identified the O5 and W2 ligands of the oxygen-evolving complex as the highly probable substrate candidates. In this work, we studied O-O bond formation between O5 and W2 based on the native Mn4Ca cluster by density functional calculations. Structural rearrangements before the formation of the S-4 state were found as a prerequisite for OAO bond formation between O5 and W2, regardless if the suggested pathways involving the typical Mn1(IV)-O- species or the recently proposed Mn-4(VII)(O)(2) species. Possible alternatives for the S-2 -> S-3 and S-3 -> S-4 transitions accounting for such required rearrangements are discussed. These findings reflect that the structural flexibility of the Mn4Ca cluster is essential to allow structural rearrangements during the catalytic cycle. (C) 2020 The Authors. Published by ELSEVIER B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences.

Automated summary

This work investigates the O-O bond formation process in the water oxidation mechanism in photosystem II, highlighting the importance of structural rearrangements and discussing possible alternative pathways for the S-2 -> S-3 and S-3 -> S-4 transitions.