title: Biological identity and diversity in photosynthesis and respiration: structure of the lumen-side domain of the chloroplast Rieske protein.
abstract: BACKGROUND
  The cytochrome b6f complex functions in oxygenic photosynthesis as an integral membrane protein complex that mediates coupled electron transfer and proton translocation. The Rieske [2Fe-2S] protein subunit of the complex functions at the electropositive (p) membrane interface as the electron acceptor for plastoquinol and donor for the cytochrome f subunit, and may have a dynamic role in catalyzing electron and proton transfer at the membrane interface. There are significant structure/function similarities to the cytochrome bc1 complex of the respiratory chain.
  
  
  RESULTS
  The 1.83 A crystal structure of a 139-residue C-terminal fragment of the Rieske [2Fe-2S] protein, derived from the cytochrome b6f complex of spinach chloroplasts, has been solved by multiwavelength anomalous diffraction. The structure of the fragment comprises two domains: a small 'cluster-binding' subdomain and a large subdomain. The [2Fe-2S] cluster-binding subdomains of the chloroplast and mitochondrial Rieske proteins are virtually identical, whereas the large subdomains are strikingly different despite a common folding topology. A structure-based sequence alignment of the b6f and bc1 groups of Rieske soluble domains is presented.
  
  
  CONCLUSIONS
  The segregation of structural conservation and divergence in the cluster-binding and large subdomains of the Rieske protein correlates with the overall relatedness of the cytochrome b6f and bc1 complexes, in which redox domains in the aqueous p phase are dissimilar and those within the membrane are similar. Distinct sequences and surface charge distributions among Rieske large subdomains may provide a signature for interaction with the p-side oxidant protein and for the pH of the intraorganelle compartment.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Carrell
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: W A
authors.initials: WA
authors.lastname: Cramer
authors.forename: J L
authors.initials: JL
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000502:physiology; D002736:Chloroplasts / Q000737:chemistry* / Q000201:enzymology; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003573:Cytochrome b Group / Q000737:chemistry; D045346:Cytochrome b6f Complex; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011522:Protons; D018724:Spinacia oleracea; D013499:Surface Properties
chemical_list: D000596:Amino Acids; D003573:Cytochrome b Group; D007506:Iron-Sulfur Proteins; D010940:Plant Proteins; D011522:Protons; C037989:Rieske iron-sulfur protein; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III; D010100:Oxygen