Complex I

Complex I (NADH:ubiquinone oxidoreductase) - provides about 40% of the proton-motive force required for ATP synthesis - mitochondrial complex I consists of 45subunits: total mass, 980 kDa - bacterial version is 550 kDa including 14 subunits conserved from bacteria to mammals - Thermus thermophilus complex has an established electron transfer pathway from NADH - to FMN to seven iron-sulphur (Fe-S) clusters to the quinone - the membrane domain contains the proton translocating machinery: three subunits homologous to Na/H antiporter. - stoichiometry: 2 electron transfer from NADH to quinone pumps 4 H + from the matrix to the cytosol - (cytosol to periplasmic space) - major source of reactive oxygen species in mitochondria

3. N. crassa (Guénebaut et al., 1997) 4. E. coli NDH-1 (Guénebaut et al., 1998) 5. Bovine heart (Grigorieff, 1998) 6. Y. lipolytica (Radermacher et al., 2006) 7 and 8. E. coli (Böttcher et al., 2002); 7 is "inactive" form, 8 is "active" form 9. Arabidopsis (Dudkina et al., 2005) 10. Bovine (Clason et al., 2010)

Architecture of the hydrophilic domain of T. thermophilus complex I. (A) Side view, with the membrane arm likely to be beneath and extending to the right, in the direction of helix H1. (B) Arrangement of redox centers. The overall orientation is similar to that in (A), tilted to provide an improved view of the FMN and the clusters. Sazanov, L. A. and Hinchliffe, P. (2006) Science 311: tunneling distance…

Berrisford J M, Sazanov L A J. Biol. Chem. 2009;284:

Efremov, R. G., Baradaran, R. and Sazanov, L. A. Nature, 465,

Left: Atomic model for the hydrophilic domain and the alpha-helical model for the membrane domain. Fe-S clusters are shown as red and yellow spheres. Each subunit is coloured differently. Right: Model of proton translocation by complex I. NADH, via FMN (magenta), donates two electrons to the chain of Fe-S clusters (red and yellow spheres), which are passed on (blue line), via terminal cluster N2, to the quinone (dark blue, moved out of the membrane by about 10 angstroms). Electron transfer is coupled to conformational changes (indicated by arrows) in the hydrophilic domain, observed for Nqo4 four-helix bundle (green cylinders) and Nqo6 helix H1 (red). These changes are transmitted to the amphipathic helix HL (magenta), which tilts three discontinuous helices (red) in antiporter-like subunits, changing the conformation of ionizable residue inside respective proton channels, resulting in translocation of three protons. The fourth proton is translocated at the interface of the two main domains. Efremov, R. G., Baradaran, R. and Sazanov, L. A. Nature, 465,

indirect pumping direct pumping

Berrisford J M, Sazanov L A J. Biol. Chem. 2009;284: ©2009 by American Society for Biochemistry and Molecular Biology direct pumping