Long-Range Interaction between the Mn4CaO5 Cluster and the Non-heme Iron Center in Photosystem II as Revealed by FTIR Spectroelectrochemistry

• Published in: Biochemistry (Easton) Vol. 53; no. 30; pp. 4914 - 4923
• Main Authors: Kato, Yuki, Noguchi, Takumi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 05.08.2014
• Subjects: Binding Sites - physiology; Calcium Compounds - chemistry; Calcium Compounds - metabolism; Crystallography, X-Ray; Electrochemical Techniques - methods; Manganese Compounds - chemistry; Manganese Compounds - metabolism; Oxides - chemistry; Oxides - metabolism; Photosystem II Protein Complex - chemistry; Photosystem II Protein Complex - metabolism; Spectroscopy, Fourier Transform Infrared - methods
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi500549b

It is known that inactivation of the Mn4CaO5 cluster, the catalytic center of water oxidation in photosystem II (PSII), induces a positive shift of the redox potential (E m) of the primary quinone electron acceptor QA by ∼+150 mV, resulting in suppression of the electron transfer from QA to the secondary quinone acceptor QB. Although the relevance of this E m(QA –/QA) shift to the photoprotection of PSII has been debated, its molecular mechanism is still enigmatic from a structural viewpoint because QA is ∼40 Å from the Mn4CaO5 cluster. In this work, we have investigated the influence of Mn depletion on the E m of the non-heme iron, which is located between QA and QB, and its surrounding structure. Electrochemical measurements in combination with Fourier transform infrared (FTIR) spectroscopy revealed that Mn depletion shifts E m(Fe2+/Fe3+) by +18 mV, which is ∼8 times smaller than the shift of E m(QA –/QA). Comparison of the Fe2+/Fe3+ FTIR difference spectra between intact and Mn-depleted PSII samples showed that Mn depletion altered the pK a’s of a His ligand to the non-heme iron, most probably the D1-His215 interacting QB, and a carboxylate group, possibly D1-Glu244, coupled with the non-heme iron. It was further shown that Mn depletion influences the CN vibration of bromoxynil bound to the QB site, indicative of the modification of the QB binding site. On the basis of these results, we discuss the mechanism of a long-range interaction between the donor and acceptor sides of PSII.