Structural Changes in the Acceptor Site of Photosystem II upon Ca2+/Sr2+ Exchange in the Mn4CaO5 Cluster Site and the Possible Long-Range Interactions.

Koua Koua

doi:10.3390/biom9080371

Abstract

The Mn4CaO5 cluster site in the oxygen-evolving complex (OEC) of photosystem II (PSII) undergoes structural perturbations, such as those induced by Ca2+/Sr2+ exchanges or Ca/Mn removal. These changes have been known to induce long-range positive shifts (between +30 and +150 mV) in the redox potential of the primary quinone electron acceptor plastoquinone A (QA), which is located 40 Å from the OEC. To further investigate these effects, we reanalyzed the crystal structure of Sr-PSII resolved at 2.1 Å and compared it with the native Ca-PSII resolved at 1.9 Å. Here, we focus on the acceptor site and report the possible long-range interactions between the donor, Mn4Ca(Sr)O5 cluster, and acceptor sites.

Highlights

Photosystem II (PSII) is a large multisubunit membrane protein complex with at least 19 subunits.In physiological conditions, it exists as a dimer with a molecular weight of ca. 0.70 MDa and is embedded in the thylakoid membranes of oxygenic photosynthetic organisms [1]
It is reasonable to attribute the shifts in the redox potential of quinone electron acceptor (QA) to the structural changes that occur upon Mn/Ca depletion or Ca2+ /Sr2+ exchanges [5,10,11,16]
A recent study that applied attenuated total reflection (ATR)-FTIR difference spectroscopy excluded the direct influence of Mn4 CaO5 cluster perturbations on the QA site [5]

Summary

Introduction

Photosystem II (PSII) is a large multisubunit membrane protein complex with at least 19 subunits.In physiological conditions, it exists as a dimer with a molecular weight of ca. 0.70 MDa and is embedded in the thylakoid membranes of oxygenic photosynthetic organisms [1]. QB H2 detaches from the QB site and moves into the plastoquinol pool in the membrane-spanning region [6]

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Results

Conclusion