Sebastian Pintscher, Rafał Pietras, Bohun Mielecki, Mateusz Szwalec, Anna Wójcik-Augustyn, Paulina Indyka, Michał Rawski, Łukasz Koziej, Marcin Jaciuk, Grzegorz Ważny, Sebastian Glatt, Artur Osyczka
{"title":"Molecular basis of plastoquinone reduction in plant cytochrome b6f","authors":"Sebastian Pintscher, Rafał Pietras, Bohun Mielecki, Mateusz Szwalec, Anna Wójcik-Augustyn, Paulina Indyka, Michał Rawski, Łukasz Koziej, Marcin Jaciuk, Grzegorz Ważny, Sebastian Glatt, Artur Osyczka","doi":"10.1038/s41477-024-01804-x","DOIUrl":null,"url":null,"abstract":"<p>A multi-subunit enzyme, cytochrome <i>b</i><sub>6</sub><i>f</i> (cyt<i>b</i><sub>6</sub><i>f</i>), provides the crucial link between photosystems I and II in the photosynthetic membranes of higher plants, transferring electrons between plastoquinone (PQ) and plastocyanin. The atomic structure of cyt<i>b</i><sub>6</sub><i>f</i> is known, but its detailed catalytic mechanism remains elusive. Here we present cryogenic electron microscopy structures of spinach cyt<i>b</i><sub>6</sub><i>f</i> at 1.9 Å and 2.2 Å resolution, revealing an unexpected orientation of the substrate PQ in the haem ligand niche that forms the PQ reduction site (Q<sub>n</sub>). PQ, unlike Q<sub>n</sub> inhibitors, is not in direct contact with the haem. Instead, a water molecule is coordinated by one of the carbonyl groups of PQ and can act as the immediate proton donor for PQ. In addition, we identify water channels that connect Q<sub>n</sub> with the aqueous exterior of the enzyme, suggesting that the binding of PQ in Q<sub>n</sub> displaces water through these channels. The structures confirm large movements of the head domain of the iron–sulfur protein (ISP-HD) towards and away from the plastoquinol oxidation site (Q<sub>p</sub>) and define the unique position of ISP-HD when a Q<sub>p</sub> inhibitor (2,5-dibromo-3-methyl-6-isopropylbenzoquinone) is bound. This work identifies key conformational states of cyt<i>b</i><sub>6</sub><i>f</i>, highlights fundamental differences between substrates and inhibitors and proposes a quinone–water exchange mechanism.</p>","PeriodicalId":18904,"journal":{"name":"Nature Plants","volume":null,"pages":null},"PeriodicalIF":15.8000,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Nature Plants","FirstCategoryId":"99","ListUrlMain":"https://doi.org/10.1038/s41477-024-01804-x","RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"PLANT SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
A multi-subunit enzyme, cytochrome b6f (cytb6f), provides the crucial link between photosystems I and II in the photosynthetic membranes of higher plants, transferring electrons between plastoquinone (PQ) and plastocyanin. The atomic structure of cytb6f is known, but its detailed catalytic mechanism remains elusive. Here we present cryogenic electron microscopy structures of spinach cytb6f at 1.9 Å and 2.2 Å resolution, revealing an unexpected orientation of the substrate PQ in the haem ligand niche that forms the PQ reduction site (Qn). PQ, unlike Qn inhibitors, is not in direct contact with the haem. Instead, a water molecule is coordinated by one of the carbonyl groups of PQ and can act as the immediate proton donor for PQ. In addition, we identify water channels that connect Qn with the aqueous exterior of the enzyme, suggesting that the binding of PQ in Qn displaces water through these channels. The structures confirm large movements of the head domain of the iron–sulfur protein (ISP-HD) towards and away from the plastoquinol oxidation site (Qp) and define the unique position of ISP-HD when a Qp inhibitor (2,5-dibromo-3-methyl-6-isopropylbenzoquinone) is bound. This work identifies key conformational states of cytb6f, highlights fundamental differences between substrates and inhibitors and proposes a quinone–water exchange mechanism.
期刊介绍:
Nature Plants is an online-only, monthly journal publishing the best research on plants — from their evolution, development, metabolism and environmental interactions to their societal significance.