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Topological organization of the Rieske iron-sulphur protein and subunit IV in the cytochrome bc1 complex of Rhodobacter sphaeroides. 1995

J Wu, and R A Niederman
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, NJ 08855-1059.

The ubiquinol-cytochrome c2 oxidoreductases (cytochrome bc1 complex) of Rhodobacter sphaeroides contains highly conserved cytochrome b, cytochrome c1 and Rieske FeS subunits, as well as a unique 14 kDa polypeptide, designated as subunit IV, thought to function as a ubiquinol-binding protein [Yu and Yu (1991) Biochemistry 30, 4934-4939]. As the topology of subunit IV is unknown and that of the FeS subunit remains a matter of debate, both the inner (cytoplasmic) and outer (periplasmic) surfaces of the intracytoplasmic membrane (ICM) were digested with proteinase K, and cleavage products were identified by immunoblotting. In uniformly oriented chromatophore vesicles (inner ICM surface exposed), fragments of approx. 4 and 1 kDa were removed from subunit IV and the FeS protein respectively. Neither subunit IV nor the FeS protein was cleaved from the outer ICM surface as exposed in osmotically protected spheroplasts or as presented to proteinase K after microencapsulation of the protease in unilamellar liposomes and fusion of these structures to chromatophore vesicles. Studies with the isolated bc1 complex, however, suggested that the C-terminal domain of the Rieske FeS, thought to reside on the periplasmic side of the ICM, was resistant to proteinase K. Overall, these results suggest a single N-terminal transmembrane helix for the FeS protein, with exposure of the N-terminus to the cytoplasm and an orientation in which a major, N-terminal portion of subunit IV is located in the cytoplasm with the predicted C-terminal transmembrane domain anchoring this polypeptide to the membrane.

UI MeSH Term Description Entries
D007506 Iron-Sulfur Proteins A group of proteins possessing only the iron-sulfur complex as the prosthetic group. These proteins participate in all major pathways of electron transport: photosynthesis, respiration, hydroxylation and bacterial hydrogen and nitrogen fixation. Iron-Sulfur Protein,Iron Sulfur Proteins,Iron Sulfur Protein,Protein, Iron-Sulfur,Proteins, Iron Sulfur,Proteins, Iron-Sulfur,Sulfur Proteins, Iron
D010446 Peptide Fragments Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques. Peptide Fragment,Fragment, Peptide,Fragments, Peptide
D002462 Cell Membrane The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells. Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D002918 Chymotrypsin A serine endopeptidase secreted by the pancreas as its zymogen, CHYMOTRYPSINOGEN and carried in the pancreatic juice to the duodenum where it is activated by TRYPSIN. It selectively cleaves aromatic amino acids on the carboxyl side. Alpha-Chymotrypsin Choay,Alphacutanée,Avazyme
D004591 Electrophoresis, Polyacrylamide Gel Electrophoresis in which a polyacrylamide gel is used as the diffusion medium. Polyacrylamide Gel Electrophoresis,SDS-PAGE,Sodium Dodecyl Sulfate-PAGE,Gel Electrophoresis, Polyacrylamide,SDS PAGE,Sodium Dodecyl Sulfate PAGE,Sodium Dodecyl Sulfate-PAGEs
D012242 Rhodobacter sphaeroides Spherical phototrophic bacteria found in mud and stagnant water exposed to light. Rhodopseudomonas sphaeroides,Rhodobacter spheroides,Rhodopseudomonas spheroides
D012697 Serine Endopeptidases Any member of the group of ENDOPEPTIDASES containing at the active site a serine residue involved in catalysis. Serine Endopeptidase,Endopeptidase, Serine,Endopeptidases, Serine
D013104 Spheroplasts Cells, usually bacteria or yeast, which have partially lost their cell wall, lost their characteristic shape and become round. Spheroplast
D014450 Electron Transport Complex III A multisubunit enzyme complex that contains CYTOCHROME B GROUP; CYTOCHROME C1; and iron-sulfur centers. It catalyzes the oxidation of ubiquinol to UBIQUINONE, and transfers the electrons to CYTOCHROME C. In MITOCHONDRIA the redox reaction is coupled to the transport of PROTONS across the inner mitochondrial membrane. Complex III,Cytochrome bc1 Complex,Ubiquinol-Cytochrome-c Reductase,Coenzyme Q-Cytochrome-c Reductase,Coenzyme QH2-Cytochrome-c Reductase,Core I Protein, UCCreductase,Core I Protein, Ubiquinol-Cytochrome c Reductase,Core II Protein, UCCreductase,Core II Protein, Ubiquinol-Cytochrome c Reductase,Cytochrome b-c2 Oxidoreductase,Cytochrome bc1,Dihydroubiquinone-Cytochrome-c Reductase,QH(2)-Cytochrome-c Reductase,QH(2)-Ferricytochrome-c Oxidoreductase,Ubihydroquinone-Cytochrome-c Reductase,Ubiquinol-Cytochrome c Reductase,Ubiquinone-Cytochrome b-c2 Oxidoreductase,Coenzyme Q Cytochrome c Reductase,Coenzyme QH2 Cytochrome c Reductase,Core I Protein, Ubiquinol Cytochrome c Reductase,Core II Protein, Ubiquinol Cytochrome c Reductase,Cytochrome b c2 Oxidoreductase,Dihydroubiquinone Cytochrome c Reductase,Reductase, Ubiquinol-Cytochrome c,Ubihydroquinone Cytochrome c Reductase,Ubiquinol Cytochrome c Reductase,Ubiquinone Cytochrome b c2 Oxidoreductase
D015151 Immunoblotting Immunologic method used for detecting or quantifying immunoreactive substances. The substance is identified by first immobilizing it by blotting onto a membrane and then tagging it with labeled antibodies. Dot Immunoblotting,Electroimmunoblotting,Immunoelectroblotting,Reverse Immunoblotting,Immunoblotting, Dot,Immunoblotting, Reverse,Dot Immunoblottings,Electroimmunoblottings,Immunoblottings,Immunoblottings, Dot,Immunoblottings, Reverse,Immunoelectroblottings,Reverse Immunoblottings

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