title: Three-dimensional structure of respiratory complex I from Escherichia coli in ice in the presence of nucleotides.
abstract: Complex I (NADH:ubiquinone oxidoreductase) is the largest protein complex of bacterial and mitochondrial respiratory chains. The first three-dimensional structure of bacterial complex I in vitrified ice was determined by electron cryo-microscopy and single particle analysis. The structure of the Escherichia coli enzyme incubated with either NAD(+) (as a reference) or NADH was calculated to 35 and 39 A resolution, respectively. The X-ray structure of the peripheral arm of Thermus thermophilus complex I was docked into the reference EM structure. The model obtained indicates that Fe-S cluster N2 is close to the membrane domain interface, allowing for effective electron transfer to membrane-embedded quinone. At the current resolution, the structures in the presence of NAD(+) or NADH are similar. Additionally, side-view class averages were calculated for the negatively stained bovine enzyme. The structures of bovine complex I in the presence of either NAD(+) or NADH also appeared to be similar. These observations indicate that conformational changes upon reduction with NADH, suggested to occur by a range of studies, are smaller than had been thought previously. The model of the entire bacterial complex I could be built from the crystal structures of subcomplexes using the EM envelope described here.
authors.affiliation: Medical Research Council, Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 2XY, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Morgan
authors.forename: Leonid A
authors.initials: LA
authors.lastname: Sazanov
mesh_terms: D020285:Cryoelectron Microscopy; D042967:Electron Transport Complex I / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008958:Models, Molecular; D009243:NAD / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D029968:Escherichia coli Proteins; D009243:NAD; D042967:Electron Transport Complex I