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Conformational Changes and H-Bond Rearrangements During Quinone Release in Photosystem II

Overview
Journal Biochemistry
Specialty Biochemistry
Date 2022 Aug 1
PMID 35914244
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Abstract

In photosystem II (PSII) and photosynthetic reaction centers from purple bacteria (PbRC), the electron released from the electronically excited chlorophyll is transferred to the terminal electron acceptor quinone, Q. Q accepts two electrons and two protons before leaving the protein. We investigated the molecular mechanism of quinone exchange in PSII, conducting molecular dynamics (MD) simulations and quantum mechanical/molecular mechanical (QM/MM) calculations. MD simulations suggest that the release of Q leads to the transformation of the short helix (D1-Phe260 to D1-Ser264), which is adjacent to the stromal helix (D1-Asn247 to D1-Ile259), into a loop and to the formation of a water-intake channel. Water molecules enter the Q binding pocket via the channel and form an H-bond network. QM/MM calculations indicate that the H-bond network serves as a proton-transfer pathway for the reprotonation of D1-His215, the proton donor during QH/QH conversion. Together with the absence of the corresponding short helix but the presence of Glu-L212 in PbRC, it seems likely that the two type-II reaction centers undergo quinone exchange via different mechanisms.

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