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Mechanism of the formation of proton transfer pathways in photosynthetic reaction centers.

ABSTRACT: In photosynthetic reaction centers from purple bacteria (PbRCs) from Rhodobacter sphaeroides, the secondary quinone Q_B accepts two electrons and two protons via electron-coupled proton transfer (PT). Here, we identify PT pathways that proceed toward the Q_B binding site, using a quantum mechanical/molecular mechanical approach. As the first electron is transferred to Q_B, the formation of the Grotthuss-like pre-PT H-bond network is observed along Asp-L213, Ser-L223, and the distal Q_B carbonyl O site. As the second electron is transferred, the formation of a low-barrier H-bond is observed between His-L190 at Fe and the proximal Q_B carbonyl O site, which facilitates the second PT. As Q_BH₂ leaves PbRC, a chain of water molecules connects protonated Glu-L212 and deprotonated His-L190 forms, which serves as a pathway for the His-L190 reprotonation. The findings of the second pathway, which does not involve Glu-L212, and the third pathway, which proceeds from Glu-L212 to His-L190, provide a mechanism for PT commonly used among PbRCs.

SUBMITTER: Sugo Y

PROVIDER: S-EPMC8325351 | biostudies-literature |

REPOSITORIES: biostudies-literature

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