Atomic structure of the entire mammalian mitochondrial complex I

Abstract

Mitochondrial complex I plays a key role in cellular energy production by transferring electrons from NADH to ubiquinone coupled to proton translocation across the membrane1,2. It is the largest protein assembly of the respiratory chain with total mass of 970 kDa3. Here we present a nearly complete atomic structure of ovine mitochondrial complex I at 3.9 Å resolution, solved by cryo-electron microscopy aided by crosslinking/mass-spectrometry mapping. All 14 conserved core and 31 mitochondria-specific supernumerary subunits are resolved within the L-shaped molecule. The hydrophilic matrix arm harbours FMN and 8 iron-sulphur clusters involved in electron transfer, and the membrane arm contains 78 transmembrane helices, mostly contributed by antiporter-like subunits involved in proton translocation. Supernumerary subunits form an interlinked, stabilizing shell around the conserved core. Tightly bound lipids (including cardiolipins) further stabilize interactions between the hydrophobic subunits. Subunits with possible regulatory roles contain additional cofactors, NADPH and two phosphopantetheine molecules, revealed to be involved in inter-subunit interactions. We observe two different conformations of the complex, which may be related to the conformationally driven coupling mechanism and to the active/deactive transition of the enzyme. Our structure provides insight into complex I mechanism, assembly, maturation and dysfunction, allowing detailed molecular analysis of disease-causing mutations.The electrochemical proton gradient across the inner mitochondrial membrane required by ATP synthase is maintained by the electron transport chain (ETC) proton-pumping complexes I, III and IV1,2. Complex I (CI) is crucial for the entire process and even mildCorrespondence and requests for materials should be addressed to L. S. (sazanov@ist.ac.at). Author Contributions: K.F. purified complex I for grid preparation, prepared cryo-EM grids, acquired and processed EM data, and co-built the models; J.A.L. purified complex I for cross-linking experiments, analysed cross-linking data and co-built the models; G.D. performed cross-linking/mass-spectrometry experiments, K.K. performed model re-building in Rosetta and sequence alignments; G.D. and M.S. analysed cross-linking data; L.A.S. designed and supervised the project, processed and analysed data and wrote the manuscript, with contributions from all authors.The authors declare no competing financial interests.Author Information: The EM maps have been deposited in the EMDataBank under accession codes . The model has been deposited in the PDB under accession code 5LNK. Europe PMC Funders GroupAuthor Manuscript Nature. Author manuscript; available in PMC 2017 April 20. Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts complex I deficiencies can cause severe pathologies4. Mammalian CI is built of 45 (44 unique) subunits. Fourteen "core" subunits, conserved from bacteria, comprise the "minimal" form of the enzyme1,5, an L-shaped structure with seven su...

Structure of human Fe–S assembly subcomplex reveals unexpected cysteine desulfurase architecture and acyl-ACP–ISD11 interactions

“…Experimental evidence supports a role of ACP-associated fatty acids in the processing of mitochondrial RNA and expression of the respiratory complexes (14,70), synthesis of Fe-S cluster cofactors (1), and achieving the mature protein assembly and active conformation for the respiratory complexes (3,23). Thus, it appears from our results and the work of others that the evolutionarily conserved pathways of Fe-S cluster biosynthesis, oxidative phosphorylation, and mtFAS have been connected by LYR proteins and their respective acyl-ACP associations.…”

“…Although the incorporation of ACP is a recently discovered component for the eukaryotic Fe-S cluster assembly machinery, its inclusion follows an emerging paradigm for interactions between mitochondrial ACP and LYR proteins (20). Previous studies demonstrate that ACP, in addition to its central role in mtFAS, forms a complex with LYRM3 and LYRM6 of Respiratory Complex I (17,18,(21)(22)(23). Similar to the SDA ec complex, the LYR motif and invariant Phe residue are required to anchor ACP to LYRM6 and to produce a functional complex (20).…”

“…One of the best known functions of the mtFAS pathway is to generate octanoyl-ACP, which is required for lipoic acid biosynthesis. However, mitochondrial ACP also functions as a required subunit for respiratory complex I and is predominately associated with the long-chain fatty acid 3-hydroxytetradecanoate (16)(17)(18)(19)(20)(21)(22)(23). More recently, ACP has been identified as an essential functional component of the eukaryotic Fe-S cluster biosynthetic complex (1).…”

Modelling the redox imbalance in Dominant Optic Atrophy: the case of respiratory Complex I

“…The values for the distances are taken from crystallographic studies (Fiedorczuk et al, 2016). Finally, we used the value λ = 0.7 eV proposed by Moser et al on an empirical basis (Moser et al, 1992).…”

“…Complex I from Bos Taurus heart mitochondria is the most studied mammalian complex I (Hirst and Roessler, 2016) and comprises 45 proteins among which 14 conserved 'core' units are sufficient to catalyse energy transduction (Fiedorczuk et al, 2016). These 14 subunits are divided into a hydrophilic redox domain and a hydrophobic domain contained in the mitochondrial inner membrane ( fig.2) and involved in protons translocation (Fiedorczuk et al, 2016).…”