title: Functional dissection of the proton pumping modules of mitochondrial complex I.
abstract: Mitochondrial complex I, the largest and most complicated proton pump of the respiratory chain, links the electron transfer from NADH to ubiquinone to the pumping of four protons from the matrix into the intermembrane space. In humans, defects in complex I are involved in a wide range of degenerative disorders. Recent progress in the X-ray structural analysis of prokaryotic and eukaryotic complex I confirmed that the redox reactions are confined entirely to the hydrophilic peripheral arm of the L-shaped molecule and take place at a remarkable distance from the membrane domain. While this clearly implies that the proton pumping within the membrane arm of complex I is driven indirectly via long-range conformational coupling, the molecular mechanism and the number, identity, and localization of the pump-sites remains unclear. Here, we report that upon deletion of the gene for a small accessory subunit of the Yarrowia complex I, a stable subcomplex (nb8mΔ) is formed that lacks the distal part of the membrane domain as revealed by single particle analysis. The analysis of the subunit composition of holo and subcomplex by three complementary proteomic approaches revealed that two (ND4 and ND5) of the three subunits with homology to bacterial Mrp-type Na(+)/H(+) antiporters that have been discussed as prime candidates for harbouring the proton pumps were missing in nb8mΔ. Nevertheless, nb8mΔ still pumps protons at half the stoichiometry of the complete enzyme. Our results provide evidence that the membrane arm of complex I harbours two functionally distinct pump modules that are connected in series by the long helical transmission element recently identified by X-ray structural analysis.
authors: Molecular Bioenergetics Group, Medical School, Cluster of Excellence Frankfurt Macromolecular Complexes, Center for Membrane Proteomics, Johann Wolfgang Goethe-Universität, Frankfurt, Germany.
authors: Stefan
authors: S
authors: Dröse
authors: Stephanie
authors: S
authors: Krack
authors: Lucie
authors: L
authors: Sokolova
authors: Klaus
authors: K
authors: Zwicker
authors: Hans-Dieter
authors: HD
authors: Barth
authors: Nina
authors: N
authors: Morgner
authors: Heinrich
authors: H
authors: Heide
authors: Mirco
authors: M
authors: Steger
authors: Esther
authors: E
authors: Nübel
authors: Volker
authors: V
authors: Zickermann
authors: Stefan
authors: S
authors: Kerscher
authors: Bernhard
authors: B
authors: Brutschy
authors: Michael
authors: M
authors: Radermacher
authors: Ulrich
authors: U
authors: Brandt
mesh_terms: D042967:Electron Transport Complex I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D057075:Enzyme Assays; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D055786:Gene Knockout Techniques; D008854:Microscopy, Electron; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008970:Molecular Weight; D011487:Protein Conformation; D017494:Proton Pumps / Q000737:chemistry / Q000378:metabolism*; D025062:Yarrowia / Q000235:genetics* / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D024101:Mitochondrial Proteins; D017494:Proton Pumps; D042967:Electron Transport Complex I