Quantum mechanics/molecular mechanics simulation of the ligand vibrations of the water-oxidizing MnM4CaO5 cluster in photosystem II

Shin Nakamura, Takumi Noguchi

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

During photosynthesis, the light-driven oxidation of water performed by photosystem II (PSII) provides electrons necessary to fix CO2, in turn supporting life on Earth by liberating molecular oxygen. Recent high-resolution X-ray images of PSII show that the wateroxidizing center (WOC) is composed of an Mn4CaO5 cluster with six carboxylate, one imidazole, and four water ligands. FTIR difference spectroscopy has shown significant structural changes of the WOC during the S-state cycle of water oxidation, especially within carboxylate groups. However, the roles that these carboxylate groups play in water oxidation as well as how they should be properly assigned in spectra are unresolved. In this study, we performed a normal mode analysis of the WOC using the quantum mechanics/molecular mechanics (QM/MM) method to simulate FTIR difference spectra on the S1to S2transition in the carboxylate stretching region. By evaluating WOC models with different oxidation and protonation states, we determined that models of high-oxidation states, Mn(III)2Mn(IV)2, satisfactorily reproduced experimental spectra from intact and Ca-depleted PSII compared with low-oxidation models. It is further suggested that the carboxylate groups bridging Ca and Mn ions within this center tune the reactivity of water ligands bound to Ca by shifting charge via their d conjugation.

Original languageEnglish
Pages (from-to)12727-12732
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume113
Issue number45
DOIs
Publication statusPublished - Nov 8 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General

Fingerprint Dive into the research topics of 'Quantum mechanics/molecular mechanics simulation of the ligand vibrations of the water-oxidizing MnM<sub>4</sub>CaO<sub>5</sub> cluster in photosystem II'. Together they form a unique fingerprint.

Cite this