Structure, biogenesis, and function of mitochondrial complex I

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NADH:ubiquinone oxidoreductase (respiratory complex I) is a very large membrane protein complex with a central function in aerobic energy metabolism. The enzyme is known to release deleterious oxygen radicals under specific conditions causing e.g. tissue damage after myocardial infarction. Dysfunction of mitochondrial complex I is implicated in a number of neuromuscular diseases and neurodegenerative conditions. We have recently solved the X-ray structure of mitochondrial complex I from the aerobic yeast Yarrowia lipolytica at 3.6 to 3.9 Å resolution. The structure offered new and exciting insights into complex I function explaining energy conversion and long range energy transfer in the large enzyme complex. For a comprehensive understanding of redox-linked proton translocation higher resolution data are needed. We propose different strategies to improve crystallization and to generate alternative crystal forms by using antibody fragments or T4 lysozyme fusions of accessory subunits. The most problematic part of the current X-ray structure is located in the upper half of the hydrophilic matrix arm of complex I. We have developed a scheme for controlled separation and purification of the soluble peripheral arm and propose to crystallize it as a discrete entity.We hypothesized that concerted structural changes at the ubiquinone reduction site trigger proton translocation. We propose to crystallize complex I variants carrying mutations of key residues to obtain insight into the structural basis of redox-linked proton translocation. The accessory NUEM subunit of complex I belongs to the large family of short-chain dehydrogenases and contains an NADPH binding site. We aim to unravel the yet unknown function of NUEM in mitochondrial metabolism and to resolve the possible interaction of NUEM with a complex I bound acyl-carrier protein.Complex I biogenesis is a complex multi-step process. Recently, we have isolated and studied an assembly intermediate that binds assembly factor N7BML (human NDUFAF2) and we hypothesized that N7BML is needed to allow interaction with the iron-sulfur cluster insertion machinery during assembly. We propose to determine the structure of the assembly intermediate by high-resolution electron microscopy.