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Interactions between the cytochrome b, cytochrome c1, and Fe-S protein subunits at the ubihydroquinone oxidation site of the bc1 complex of Rhodobacter capsulatus. 1998

A S Saribaş, and M Valkova-Valchanova, and M K Tokito, and Z Zhang, and E A Berry, and F Daldal
Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia 19104, USA.

Ubihydroquinone:cytochrome (cyt) c oxidoreductase (bc1 complex and its plant counterpart b6f complex) is a vital component of energy-transducing systems in most organisms from bacteria to eukaryotes. In the facultative phototrophic (Ps) bacterium Rhodobacter capsulatus, it is constituted by the cyt b, cyt c1, and Rieske Fe-S protein subunits and is essential for Ps growth. Of these subunits, cyt b has two nontransmembrane helices, cd1 and cd2, which are critical for its structure and function. In particular, substitution of threonine (T) at position 163 on cd1 with phenylalanine (F) or proline (P) leads to the absence of the bc1 complex. Here, Ps+ revertants of B:T163F were obtained, and their detailed characterizations indicated that position 163 is important for the assembly of the bc1 complex by mediating subunit interactions at the Qo site. The loss of the hydroxyl group at position 163 of cyt b was compensated for by the gain of either a hydroxyl group at position 182 of cyt b or 46 of the Fe-S protein or a sulfhydryl group at position 46 of cyt c1. Examination of the mitochondrial bc1 complex crystal structure [Zhang, Z., Huang, L., Shulmeister, V. M., Chi, Y.-I., Kim, K. K., Hung, L.-W., Crofts, A. R., Berry, E. A., and Kim, S.-H. (1998) Nature 392, 677-684] revealed that the counterparts of B:G182 (i.e., G167) and F:A46 (i.e. , A70) are located close to B:T163 (i.e., T148), whereas the C:R46 (i.e., R28) is remarkably far from it. The revertants contained substoichiometric amounts of the Fe-S protein subunit and exhibited steady-state and single-turnover, electron transfer activities lower than that of a wild-type bc1 complex. Interestingly, their membrane supernatants contained a smaller form of this subunit with physicochemical properties identical to those of its membrane-bound form. Determination of the amino-terminal amino acid sequence of this soluble Fe-S protein revealed that it was derived from the wild-type protein by proteolytic cleavage at V44. This work revealed for the first time that position 163 of cyt b is important both for proper subunit interactions at the Qo site and for inactivation of the bc1 complex by proteolytic cleavage of its Fe-S protein subunit at a region apparently responsible for its mobility during Qo site catalysis.

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
D008958 Models, Molecular Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures. Molecular Models,Model, Molecular,Molecular Model
D010084 Oxidation-Reduction A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471). Redox,Oxidation Reduction
D010641 Phenotype The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment. Phenotypes
D010649 Phenylalanine An essential aromatic amino acid that is a precursor of MELANIN; DOPAMINE; noradrenalin (NOREPINEPHRINE), and THYROXINE. Endorphenyl,L-Phenylalanine,Phenylalanine, L-Isomer,L-Isomer Phenylalanine,Phenylalanine, L Isomer
D003573 Cytochrome b Group Cytochromes (electron-transporting proteins) with protoheme (HEME B) as the prosthetic group. Cytochromes Type b,Cytochromes, Heme b,Group, Cytochrome b,Heme b Cytochromes,Type b, Cytochromes,b Cytochromes, Heme,b Group, Cytochrome
D003575 Cytochromes c1 The 30-kDa membrane-bound c-type cytochrome protein of mitochondria that functions as an electron donor to CYTOCHROME C GROUP in the mitochondrial and bacterial RESPIRATORY CHAIN. (From Enzyme Nomenclature, 1992, p545) Cytochrome c1,Cytochrome c-1,Cytochrome c 1
D001665 Binding Sites The parts of a macromolecule that directly participate in its specific combination with another molecule. Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D012995 Solubility The ability of a substance to be dissolved, i.e. to form a solution with another substance. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed) Solubilities
D013489 Suppression, Genetic Mutation process that restores the wild-type PHENOTYPE in an organism possessing a mutationally altered GENOTYPE. The second "suppressor" mutation may be on a different gene, on the same gene but located at a distance from the site of the primary mutation, or in extrachromosomal genes (EXTRACHROMOSOMAL INHERITANCE). Suppressor Mutation,Genetic Suppression,Genetic Suppressions,Mutation, Suppressor,Mutations, Suppressor,Suppressions, Genetic,Suppressor Mutations

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