A novel electron transfer mechanism suggested by crystallographic studies of mitochondrial cytochrome bc1 complex

The crystal structure of bovine mitochondrial cytochrome bc1 complex, an integral membrane protein complex of 11 different subunits with a total molecular mass of 242 kDa, demonstrated a tightly associated dimer consisting of three major regions: a matrix region primarily made of subunits core1, core2, 6, and 9; a transmembrane-helix region of 26 helices in the dimer contributed by cytochrome b, cytochrome c1, the Rieske iron-sulfur protein (ISP), subunits 7, 10, and 11; and an intermembrane-space region composed of extramembrane domains of ISP, cytochrome c1, and subunit 8. The structure also revealed the positions of and distances between irons of prosthetic groups, and two symmetry related cavities in the transmembrane-helix region upon dimerization of the bc1 complex. Extensive crystallographic studies on crystals of bc1 complexed with inhibitors of electron transfer identified binding pockets for both Qo and Qi site inhibitors. Discrete binding sites for subtypes of Qo site inhibitors have been mapped onto the Qo binding pocket, and bindings of different subtypes of Qo site inhibitors are capable of inducing dramatic conformational changes in the extramembrane domain of ISP. A novel electron transfer mechanism for the bc1 complex consistent with crystallographic observations is discussed.Key words: bc1 complex, electron transfer, structure, conformational change, inhibitor.

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Deletion of QCR6, the gene encoding subunit six of the mitochondrial cytochrome bc1 complex, blocks maturation of cytochrome c1, and causes temperature-sensitive petite growth in Saccharomyces cerevisiae.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(17)42253-8 ◽

1994 ◽

Vol 269 (2) ◽

pp. 1270-1275

Author(s):

M. Yang ◽

B.L. Trumpower

Keyword(s):

Saccharomyces Cerevisiae ◽

Cytochrome Bc1 ◽

Temperature Sensitive ◽

Mitochondrial Cytochrome ◽

Bc1 Complex ◽

Cytochrome Bc1 Complex ◽

Gene Encoding ◽

Cytochrome C1

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Assignment of the Gene for the Cytochrome c1 Subunit of the Mitochondrial Cytochrome bc1 Complex (CYC1) to Human Chromosome 8q24.3

Genomics ◽

10.1006/geno.1994.1084 ◽

1994 ◽

Vol 19 (2) ◽

pp. 400-401 ◽

Cited By ~ 3

Author(s):

Alessandra M.V. Duncan ◽

Takayuki Ozawa ◽

Hiroshi Suzuki ◽

Rima Rozen

Keyword(s):

Human Chromosome ◽

Cytochrome Bc1 ◽

Mitochondrial Cytochrome ◽

Bc1 Complex ◽

Cytochrome Bc1 Complex ◽

Cytochrome C1

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A structural analysis of the transient interaction between the cytochrome bc1 complex and its substrate cytochrome c

Biochemical Society Transactions ◽

10.1042/bst0360981 ◽

2008 ◽

Vol 36 (5) ◽

pp. 981-985 ◽

Cited By ~ 12

Author(s):

Ajeeta Nyola ◽

Carola Hunte

Keyword(s):

Electron Transfer ◽

Cytochrome C ◽

Cytochrome Bc1 ◽

Cellular Respiration ◽

Bc1 Complex ◽

Cytochrome Bc1 Complex ◽

Binding Interaction ◽

Cytochrome C1 ◽

Charged Residues ◽

Electron Transfer Complex

In cellular respiration, cytochrome c transfers electrons from the cytochrome bc1 complex to cytochrome c oxidase by transiently binding to the membrane proteins. The first X-ray structure of the yeast cytochrome bc1 complex with bound cytochrome c revealed the general architecture of the electron-transfer complex. The interface of the complex is small. The haem moieties are centrally located in a mainly non-polar contact site, which includes a cation–π interaction and is surrounded by complementary charged residues. Only one cytochrome c1-docking site of the dimeric complex is occupied with cytochrome c. The recent 1.9 Å (1 Å=0.1 nm) resolution structure of the complex showed that the interface is highly hydrated. With cytochrome c bound, a higher number of interfacial water molecules are present on the cytochrome c1 interface, whereas its protein surface is not affected. Remarkably, the dimer structure is slightly asymmetric. Univalent cytochrome c binding coincides with conformational changes of the Rieske head domain and subunit QCR6p. Pronounced hydration and a mobility mismatch at the interface with disordered charged residues on the cytochrome c side are favourable for transient binding. Comparison with a new structure of the complex with bound isoform-2 cytochrome c led to the definition of a core interface, which refers to four common interaction pairs including the cation–π interaction. They encircle the haem groups and are surrounded by variable interactions. The core interface may be a feature to gain specificity for formation of the reactive complex. The consistency in the binding interaction despite differences in primary sequence, redox state and crystal contacts, together with crystallization at physiological ionic strength, clearly suggest that the structures show the native bound state of the electron-transfer complex.

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

Biochemical Journal ◽

10.1042/bj3050823 ◽

1995 ◽

Vol 305 (3) ◽

pp. 823-828 ◽

Cited By ~ 3

Author(s):

J Wu ◽

R A Niederman

Keyword(s):

Rhodobacter Sphaeroides ◽

Transmembrane Domain ◽

Transmembrane Helix ◽

Proteinase K ◽

Cytochrome Bc1 ◽

Bc1 Complex ◽

Cytochrome Bc1 Complex ◽

Intracytoplasmic Membrane ◽

Cytochrome C2 ◽

Cytochrome C1

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.

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