A long road towards the structure of respiratory complex I, a giant molecular proton pump.
Complex I (NADH:ubiquinone oxidoreductase) is central to cellular energy production, being the first and largest enzyme of the respiratory chain in mitochondria. It couples electron transfer from NADH to ubiquinone with proton translocation across the inner mitochondrial membrane and is involved in a wide range of human neurodegenerative disorders. Mammalian complex I is composed of 44 different subunits, whereas the 'minimal' bacterial version contains 14 highly conserved 'core' subunits. The L-shaped assembly consists of hydrophilic and membrane domains. We have determined all known atomic structures of complex I, starting from the hydrophilic domain of Thermus thermophilus enzyme (eight subunits, nine Fe-S clusters), followed by the membrane domains of the Escherichia coli (six subunits, 55 transmembrane helices) and T. thermophilus (seven subunits, 64 transmembrane helices) enzymes, and finally culminating in a recent crystal structure of the entire intact complex I from T. thermophilus (536 kDa, 16 subunits, nine Fe-S clusters, 64 transmembrane helices). The structure suggests an unusual and unique coupling mechanism via long-range conformational changes. Determination of the structure of the entire complex was possible only through this step-by-step approach, building on from smaller subcomplexes towards the entire assembly. Large membrane proteins are notoriously difficult to crystallize, and so various non-standard and sometimes counterintuitive approaches were employed in order to achieve crystal diffraction to high resolution and solve the structures. These steps, as well as the implications from the final structure, are discussed in the present review.
*Medical Research Council Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, U.K.
Leonid A
LA
Sazanov
Rozbeh
R
Baradaran
Rouslan G
RG
Efremov
John M
JM
Berrisford
Gurdeep
G
Minhas
D042967:Electron Transport Complex I / Q000737:chemistry*; D004734:Energy Metabolism; D004926:Escherichia coli / Q000201:enzymology; D006801:Humans; D051336:Mitochondrial Membranes / Q000737:chemistry; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D017494:Proton Pumps / Q000737:chemistry*; D016963:Thermus thermophilus / Q000201:enzymology
D046912:Multiprotein Complexes; D021122:Protein Subunits; D017494:Proton Pumps; D042967:Electron Transport Complex I