The enzymes of the bc1 complex family (ubiquinol:cytochrome c oxidoreductases, and the closely related b6f complex of oxygenic photosynthesis), carry the energy flux of the biosphere, serving as the central enzymes of respiratory and photosynthetic electron transfer chains.
The aim of this project has been to understand how these important enzymes function. X-ray crystallographic structures for several mitochondrial complexes have recently been solved in collaboration with Dr. Ed Berry, and an extensive analysis in the light of previous work has provide new insights on function. Much biophysical work has established the basic mechanism, and the focus in recent years has been on putting this into a structural context. The complexes catalyze the oxidation of ubiquinol and the reduction of cytochrome c through a modified Q-cycle. Three catalytic subunits, a cytochrome b with two hemes, cytochrome c1 and an iron sulfur protein, house the mechanism. These are well conserved across the bacterial/mitochondrial divide. Two separate internal electron transfer chains connect three catalytic sites that catalyze oxidation and reduction of the quinone pool, and reduction of cytochrome c. Electron transfer across the membrane, and coupling of these redox reactions to the release or uptake of protons, allows the complex to generate the transmembrane gradient that drives ATP synthesis. From our analysis of the structure, we have suggested some novel extensions of this basic mechanism, including a dramatic movement of the iron sulfur protein between its two reaction partners, a revised mechanism for the reaction by which quinol is oxidized, and a more detailed understanding of the quinone reduction site. In the renewal period, we will make use of the structure in an extended exploration of the molecular mechanism, using spectroscopic methods, and biophysical, molecular engineering and biochemical protocols developed under the grant. Apart from its intrinsic interest, the bc1 complex is a major site of production of oxygen radicals, which cause cell aging and DNA damage leading to cancer, and also the locus of inherited genetic diseases. Natural inhibitors block turnover by mimicking quinone at the catalytic sites, and commercial interest has centered on the possibility of using these as green pesticides.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM035438-16
Application #
6627143
Study Section
Physical Biochemistry Study Section (PB)
Program Officer
Preusch, Peter C
Project Start
1999-01-01
Project End
2003-12-31
Budget Start
2003-01-01
Budget End
2003-12-31
Support Year
16
Fiscal Year
2003
Total Cost
$262,403
Indirect Cost
Name
University of Illinois Urbana-Champaign
Department
Microbiology/Immun/Virology
Type
Schools of Arts and Sciences
DUNS #
041544081
City
Champaign
State
IL
Country
United States
Zip Code
61820
Wilson, Charles A; Crofts, Antony R (2018) Dissecting the pattern of proton release from partial process involved in ubihydroquinone oxidation in the Q-cycle. Biochim Biophys Acta Bioenerg 1859:531-543
Barragan, Angela M; Crofts, Antony R; Schulten, Klaus et al. (2015) Identification of ubiquinol binding motifs at the Qo-site of the cytochrome bc1 complex. J Phys Chem B 119:433-47
Crofts, Antony R; Hong, Sangjin; Wilson, Charles et al. (2013) The mechanism of ubihydroquinone oxidation at the Qo-site of the cytochrome bc1 complex. Biochim Biophys Acta 1827:1362-77
Victoria, Doreen; Burton, Rodney; Crofts, Antony R (2013) Role of the -PEWY-glutamate in catalysis at the Q(o)-site of the Cyt bc(1) complex. Biochim Biophys Acta 1827:365-86
Hong, Sangjin; Victoria, Doreen; Crofts, Antony R (2012) Inter-monomer electron transfer is too slow to compete with monomeric turnover in bc(1) complex. Biochim Biophys Acta 1817:1053-62
Samoilova, Rimma I; Crofts, Antony R; Dikanov, Sergei A (2011) Reaction of superoxide radical with quinone molecules. J Phys Chem A 115:11589-93
Lhee, Sangmoon; Kolling, Derrick R J; Nair, Satish K et al. (2010) Modifications of protein environment of the [2Fe-2S] cluster of the bc1 complex: effects on the biophysical properties of the rieske iron-sulfur protein and on the kinetics of the complex. J Biol Chem 285:9233-48
Dikanov, Sergei A; Samoilova, Rimma I; Kappl, Reinhard et al. (2009) The reduced [2Fe-2S] clusters in adrenodoxin and Arthrospira platensis ferredoxin share spin density with protein nitrogens, probed using 2D ESEEM. Phys Chem Chem Phys 11:6807-19
Kolling, Derrick R J; Samoilova, Rimma I; Shubin, Alexander A et al. (2009) Proton environment of reduced Rieske iron-sulfur cluster probed by two-dimensional ESEEM spectroscopy. J Phys Chem A 113:653-67
Crofts, Antony R; Holland, J Todd; Victoria, Doreen et al. (2008) The Q-cycle reviewed: How well does a monomeric mechanism of the bc(1) complex account for the function of a dimeric complex? Biochim Biophys Acta 1777:1001-19

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