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Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2026,9,8]]},"abstract":"<jats:p>\n                    The function of cytochrome bc\n                    <jats:sub>1<\/jats:sub>\n                    , a widespread energy-conserving enzyme, requires the coordinated activity of two quinone-binding sites (Q\n                    <jats:sub>o<\/jats:sub>\n                    catalyzing oxidation of ubiquinol and Q\n                    <jats:sub>i<\/jats:sub>\n                    catalyzing reduction of ubiquinone). The operation of Q\n                    <jats:sub>o<\/jats:sub>\n                    , but not Q\n                    <jats:sub>i<\/jats:sub>\n                    , involves large-scale movement of the head domain of iron-sulfur protein (ISP-HD). How the respective sites accommodate quinone molecules for efficient catalysis remains elusive. Here, we present high-resolution cryoelectron microscopy structures of bacterial cytochrome bc\n                    <jats:sub>1<\/jats:sub>\n                    with native ubiquinone molecules in various states. They show that the quinone headgroup occupies a catalytically competent position in Q\n                    <jats:sub>o<\/jats:sub>\n                    only when the ISP-HD interacts with cytochrome b. When the ISP-HD does not interact with this subunit, quinone is present in the hydrophobic groove, however its headgroup is prevented from reaching the catalytic cavity by steric hindrance. In this state, the position of quinone headgroup is clearly not fixed. In contrast, all structures show Q\n                    <jats:sub>i<\/jats:sub>\n                    in the same state with a well-resolved and catalytically competent quinone headgroup, but with its tail not fixed. These distinctly different ubiquinone binding modes for Q\n                    <jats:sub>o<\/jats:sub>\n                    and Q\n                    <jats:sub>i<\/jats:sub>\n                    secure the smooth operation of cytochrome bc\n                    <jats:sub>1<\/jats:sub>\n                    .\n                  <\/jats:p>","DOI":"10.1073\/pnas.2618242123","type":"journal-article","created":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T17:58:11Z","timestamp":1788285491000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":1,"title":["Distinct ubiquinone binding at the oxidation and reduction sites of cytochrome bc\n                    <sub>1<\/sub>"],"prefix":"10.1073","volume":"123","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8424-6590","authenticated-orcid":false,"given":"Rafa\u0142","family":"Pietras","sequence":"first","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"Faculty of Biochemistry, Biophysics and Biotechnology, Department of Molecular Biophysics, Jagiellonian University","place":["Krak\u00f3w, Poland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3053-093X","authenticated-orcid":false,"given":"Anna","family":"W\u00f3jcik-Augustyn","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"Faculty of Biochemistry, Biophysics and Biotechnology, Department of Molecular Biophysics, Jagiellonian University","place":["Krak\u00f3w, Poland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bohun","family":"Mielecki","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"Faculty of Biochemistry, Biophysics and Biotechnology, Department of Molecular Biophysics, Jagiellonian University","place":["Krak\u00f3w, Poland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6813-5997","authenticated-orcid":false,"given":"Marcin","family":"Sarewicz","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"Faculty of Biochemistry, Biophysics and Biotechnology, Department of Molecular Biophysics, Jagiellonian University","place":["Krak\u00f3w, Poland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marcin","family":"Jaciuk","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"Ma\u0142opolska Centre of Biotechnology, Jagiellonian University","place":["Krak\u00f3w, Poland"]},{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"National Synchrotron Radiation Centre SOLARIS, Jagiellonian University","place":["Krak\u00f3w, Poland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"\u0141ukasz","family":"Koziej","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03bqmcz70","id-type":"ROR","asserted-by":"publisher"}],"name":"Ma\u0142opolska Centre of Biotechnology, Jagiellonian University","place":["Krak\u00f3w, 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Deposited 19 April 2026."},{"key":"e_1_3_4_66_2","unstructured":"R. Pietras Single-particle cryo-EM dataset of Rhodobacter capsulatus cytochrome bc1 complex with 2-alanine insertion in the neck region of iron-sulphur protein (+2Ala mutant). Electron Microscopy Public Image Archive. https:\/\/www.ebi.ac.uk\/empiar\/EMPIAR-13503. Deposited 22 April 2026."},{"key":"e_1_3_4_67_2","doi-asserted-by":"crossref","unstructured":"R. Pietras Cryo-EM structure of Rhodobacter capsulatus cytochrome bc1 dimer at 2.16 A resolution with water molecules and quinone in the quinone reduction site. Protein Data Bank. https:\/\/doi.org\/10.2210\/pdb29xz\/pdb. Deposited 14 April 2026.","DOI":"10.2210\/pdb29xz\/pdb"},{"key":"e_1_3_4_68_2","doi-asserted-by":"crossref","unstructured":"R. Pietras Cryo-EM structure of Rhodobacter capsulatus cytochrome bc1 dimer with one Rieske protein in the c position and one in the b position and quinone in the quinone oxidation site. 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Pietras R. capsulatus cytochrome bc1 dimer with both Rieske proteins in the b position. Electron Microscopy Data Bank. https:\/\/www.ebi.ac.uk\/emdb\/EMD-57442. Deposited 14 April 2026."},{"key":"e_1_3_4_76_2","unstructured":"R. Pietras R. capsulatus cytochrome bc1 dimer with both Rieske proteins in the c position. Electron Microscopy Data Bank. https:\/\/www.ebi.ac.uk\/emdb\/EMD-57443. Deposited 14 April 2026."},{"key":"e_1_3_4_77_2","unstructured":"R. Pietras R. capsulatus cytochrome bc1 dimer with one Rieske protein in the c position and one in an intermediate position. Electron Microscopy Data Bank. https:\/\/www.ebi.ac.uk\/emdb\/EMD-57444. Deposited 14 April 2026."},{"key":"e_1_3_4_78_2","unstructured":"R. Pietras Rhodobacter capsulatus +2Ala insertion mutant of cytochrome bc1 dimer at 2.41 A. Electron Microscopy Data Bank. https:\/\/www.ebi.ac.uk\/emdb\/EMD-57445. Deposited 14 April 2026."}],"container-title":["Proceedings of the National Academy of Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pnas.org\/doi\/pdf\/10.1073\/pnas.2618242123","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T17:58:19Z","timestamp":1788285499000},"score":1,"resource":{"primary":{"URL":"https:\/\/pnas.org\/doi\/10.1073\/pnas.2618242123"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,1]]},"references-count":78,"journal-issue":{"issue":"36","published-print":{"date-parts":[[2026,9,8]]}},"alternative-id":["10.1073\/pnas.2618242123"],"URL":"https:\/\/doi.org\/10.1073\/pnas.2618242123","relation":{},"ISSN":["0027-8424","1091-6490"],"issn-type":[{"value":"0027-8424","type":"print"},{"value":"1091-6490","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,1]]},"assertion":[{"value":"2026-05-27","order":0,"name":"received","label":"Received","group":{"name":"publication_history","label":"Publication History"}},{"value":"2026-08-02","order":2,"name":"accepted","label":"Accepted","group":{"name":"publication_history","label":"Publication History"}},{"value":"2026-09-01","order":3,"name":"published","label":"Published","group":{"name":"publication_history","label":"Publication History"}}],"article-number":"e2618242123"}}