Mechanism of the formation of proton transfer pathways in photosynthetic reaction centers
| Autor: | Yu Sugo, Keisuke Saito, Hiroshi Ishikita |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Photosynthetic reaction centre
proton-coupled electron transfer low-barrier hydrogen bond Photosystem II Photosynthetic Reaction Center Complex Proteins Low-barrier hydrogen bond Protonation Rhodobacter sphaeroides 02 engineering and technology 010402 general chemistry Photochemistry Biochemistry 01 natural sciences Purple bacteria Electron Transport Deprotonation Binding Sites Multidisciplinary biology Chemistry Quinones photosystem II Biological Sciences 021001 nanoscience & nanotechnology biology.organism_classification 0104 chemical sciences artificial photosynthesis Protons Proton-coupled electron transfer conformational gating 0210 nano-technology |
| Zdroj: | Proceedings of the National Academy of Sciences of the United States of America |
| ISSN: | 1091-6490 0027-8424 |
| DOI: | 10.1073/pnas.2103203118 |
| Popis: | Significance The crystal structures of photosynthetic reaction centers from purple bacteria (PbRCs) and photosystem II show large structural similarity. However, the proposed mechanisms of proton transfer toward the terminal electron acceptor quinone (QB) are not consistent. In particular, not His-L190, which is an H-bond partner of QB, but rather Glu-L212, which is ∼6 Å away from QB, was assumed to be the direct proton donor for QB. We demonstrate that the H-bond between His-L190 and QB is a low-barrier H-bond, which facilitates proton transfer from singly protonated His-L190 to QB. Furthermore, Glu-L212 is not a direct H-bond donor for QB. However, it facilitates proton transfer toward deprotonated His-L190 via water molecules after QBH2 forms and leaves the PbRC. In photosynthetic reaction centers from purple bacteria (PbRCs) from Rhodobacter sphaeroides, the secondary quinone QB accepts two electrons and two protons via electron-coupled proton transfer (PT). Here, we identify PT pathways that proceed toward the QB binding site, using a quantum mechanical/molecular mechanical approach. As the first electron is transferred to QB, the formation of the Grotthuss-like pre-PT H-bond network is observed along Asp-L213, Ser-L223, and the distal QB 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 QB carbonyl O site, which facilitates the second PT. As QBH2 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. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|