title: Transmembrane traffic in the cytochrome b6f complex.
abstract: Crystal structures and their implications for function are described for the energy transducing hetero-oligomeric dimeric cytochrome b6f complex of oxygenic photosynthesis from the thermophilic cyanobacterium, Mastigocladus laminosus, and the green alga, Chlamydomonas reinhardtii. The complex has a cytochrome b core and a central quinone exchange cavity, defined by the two monomers that are very similar to those in the respiratory cytochrome bc1 complex. The pathway of quinol/quinone (Q/QH2) transfer emphasizes the labyrinthine internal structure of the complex, including an 11x12 A portal through which Q/QH2, containing a 45-carbon isoprenoid chain, must pass. Three prosthetic groups are present in the b6f complex that are not found in the related bc1 complex: a chlorophyll (Chl) a, a beta-carotene, and a structurally unique covalently bound heme that does not possess amino acid side chains as axial ligands. It is hypothesized that this heme, exposed to the cavity and a neighboring plastoquinone and close to the positive surface potential of the complex, can function in cyclic electron transport via anionic ferredoxin.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-2054, USA. waclab@purdue.edu
authors.forename: William A
authors.initials: WA
authors.lastname: Cramer
authors.forename: Huamin
authors.initials: H
authors.lastname: Zhang
authors.forename: Jiusheng
authors.initials: J
authors.lastname: Yan
authors.forename: Genji
authors.initials: G
authors.lastname: Kurisu
authors.forename: Janet L
authors.initials: JL
authors.lastname: Smith
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D000460:Chlorophyta / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D045346:Cytochrome b6f Complex / Q000378:metabolism*; D019281:Dimerization; D004579:Electron Transport / Q000502:physiology; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006873:Hydroquinones / Q000737:chemistry / Q000378:metabolism; D008055:Lipids / Q000737:chemistry; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation
chemical_list: D020418:Algal Proteins; D001426:Bacterial Proteins; D006873:Hydroquinones; D008055:Lipids; D006418:Heme; D045346:Cytochrome b6f Complex