{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,8,6]],"date-time":"2025-08-06T13:05:09Z","timestamp":1754485509037},"reference-count":34,"publisher":"Proceedings of the National Academy of Sciences","issue":"25","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[1997,12,9]]},"abstract":"<jats:p>\n            Photosystem II is a reaction center protein complex located in photosynthetic membranes of plants, algae, and cyanobacteria. Using light energy, photosystem II catalyzes the oxidation of water and the reduction of plastoquinone, resulting in the release of molecular oxygen. A key component of photosystem II is cytochrome\n            <jats:italic>b<\/jats:italic>\n            <jats:sub>559<\/jats:sub>\n            , a membrane-embedded heme protein with an unknown function. The cytochrome is unusual in that a heme links two separate polypeptide subunits, \u03b1 and \u03b2, either as a heterodimer (\u03b1\u03b2) or as two homodimers (\u03b1\n            <jats:sub>2<\/jats:sub>\n            and \u03b2\n            <jats:sub>2<\/jats:sub>\n            ). To determine the structural organization of cytochrome\n            <jats:italic>b<\/jats:italic>\n            <jats:sub>559<\/jats:sub>\n            in the membrane, we used site-directed mutagenesis to fuse the coding regions of the two respective genes in the cyanobacterium\n            <jats:italic>Synechocystis<\/jats:italic>\n            sp. PCC 6803. In this construction, the C terminus of the \u03b1 subunit (9 kDa) is attached to the N terminus of the \u03b2 subunit (5 kDa) to form a 14-kDa \u03b1\u03b2 fusion protein that is predicted to have two membrane-spanning \u03b1-helices with antiparallel orientations. Cells containing the \u03b1\u03b2 fusion protein grow photoautotrophically and assemble functional photosystem II complexes. Optical spectroscopy shows that the \u03b1\u03b2 fusion protein binds heme and is incorporated into photosystem II. These data support a structural model of cytochrome\n            <jats:italic>b<\/jats:italic>\n            <jats:sub>559<\/jats:sub>\n            in which one heme is coordinated to an \u03b1\n            <jats:sub>2<\/jats:sub>\n            homodimer and a second heme is coordinated to a \u03b2\n            <jats:sub>2<\/jats:sub>\n            homodimer. In this model, each photosystem II complex contains two cytochrome\n            <jats:italic>b<\/jats:italic>\n            <jats:sub>559<\/jats:sub>\n            hemes, with the \u03b1\n            <jats:sub>2<\/jats:sub>\n            heme located near the stromal side of the membrane and the \u03b2\n            <jats:sub>2<\/jats:sub>\n            heme located near the lumenal side.\n          <\/jats:p>","DOI":"10.1073\/pnas.94.25.14173","type":"journal-article","created":{"date-parts":[[2002,7,26]],"date-time":"2002-07-26T14:31:39Z","timestamp":1027693899000},"page":"14173-14178","update-policy":"http:\/\/dx.doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":16,"title":["Structural model of cytochrome\n            <i>b<\/i>\n            <sub>559<\/sub>\n            in photosystem II based on a mutant with genetically\u2009fused\u2009subunits"],"prefix":"10.1073","volume":"94","author":[{"given":"Vincent P.","family":"McNamara","sequence":"first","affiliation":[{"name":"Department of Plant Biology and Photosynthesis Research Unit, U.S. Department of Agriculture\/Agricultural Research Service, University of Illinois, Urbana, IL 61801; and Department of Biology, Box 1137, Washington University, St. Louis, MO 63130"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Fayyaz S.","family":"Sutterwala","sequence":"additional","affiliation":[{"name":"Department of Plant Biology and Photosynthesis Research Unit, U.S. Department of Agriculture\/Agricultural Research Service, University of Illinois, Urbana, IL 61801; and Department of Biology, Box 1137, Washington University, St. Louis, MO 63130"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Himadri B.","family":"Pakrasi","sequence":"additional","affiliation":[{"name":"Department of Plant Biology and Photosynthesis Research Unit, U.S. Department of Agriculture\/Agricultural Research Service, University of Illinois, Urbana, IL 61801; and Department of Biology, Box 1137, Washington University, St. Louis, MO 63130"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"John","family":"Whitmarsh","sequence":"additional","affiliation":[{"name":"Department of Plant Biology and Photosynthesis Research Unit, U.S. Department of Agriculture\/Agricultural Research Service, University of Illinois, Urbana, IL 61801; and Department of Biology, Box 1137, Washington University, St. Louis, MO 63130"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"341","published-online":{"date-parts":[[1997,12,9]]},"reference":[{"key":"e_1_3_2_1_2","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.ge.29.120195.003543"},{"key":"e_1_3_2_2_2","doi-asserted-by":"publisher","DOI":"10.1021\/cr950052k"},{"key":"e_1_3_2_3_2","doi-asserted-by":"publisher","DOI":"10.1016\/0005-2728(92)90133-M"},{"key":"e_1_3_2_4_2","doi-asserted-by":"publisher","DOI":"10.1111\/j.1399-3054.1993.tb01392.x"},{"key":"e_1_3_2_5_2","doi-asserted-by":"publisher","DOI":"10.1007\/BF00831536"},{"key":"e_1_3_2_6_2","first-page":"249","volume-title":"Oxygenic Photosynthesis: The Light Reactions","author":"Whitmarsh J","year":"1996","unstructured":"J Whitmarsh, H B Pakrasi Oxygenic Photosynthesis: The Light Reactions, eds D R Ort, C F Yocum (Kluwer, Dordrecht, the Netherlands), pp. 249\u2013264 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