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

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• 作者：Yuki Kato ; Takumi Noguchi
• 刊名：Biochemistry
• 出版年：2014
• 出版时间：August 5, 2014
• 年：2014
• 卷：53
• 期：30
• 页码：4914-4923
• 全文大小：479K
• ISSN：1520-4995

文摘

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 Q_A by +150 mV, resulting in suppression of the electron transfer from Q_A to the secondary quinone acceptor Q_B. Although the relevance of this E_m(Q_A^{鈥?/sup>/Q_A) shift to the photoprotection of PSII has been debated, its molecular mechanism is still enigmatic from a structural viewpoint because Q_A is 40 脜 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 Q_A and Q_B, 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(Q_A鈥?/sup>/Q_A). Comparison of the Fe2+/Fe3+ FTIR difference spectra between intact and Mn-depleted PSII samples showed that Mn depletion altered the pK_a鈥檚 of a His ligand to the non-heme iron, most probably the D1-His215 interacting Q_B, and a carboxylate group, possibly D1-Glu244, coupled with the non-heme iron. It was further shown that Mn depletion influences the C鈮 vibration of bromoxynil bound to the Q_B site, indicative of the modification of the Q_B 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.}