光合成酸素発生マンガンクラスターの機能発現に見る「歪んだ椅子」型構造の重要性

Abstract

This account describes a current summary of our computational studies intended to elucidate the mechanism underlying water oxidation by the tetranuclear Mn cluster in the oxygen-evolving complex of photosystem II, the most fundamental bioenergetic process required for the maintenance of life. We focus herein on several important findings about the relatively high oxidation (S2 and S3) states of the cluster that involve three or four MnIV and one or no MnIII ions. The presentation is designed to highlight how the cluster stores the oxidizing power, binds substrate water molecules, and activates them. We discuss the fundamental importance of the cooperative effects of multiple Jahn–Teller axes on MnIII ions, which inevitably deform the cluster structure in such a direction as to promote substrate binding during S2 → S3 transition and O–O bond formation in the S3 state. Our interpretation is that the “distorted chair” topology of the cluster is the heart of efficient catalysis for oxygen evolution, and the presentation attempts to reflect this view.