3D Reconstruction of a Subcomplex of NADH-ubiquinone-oxidoreductase (Complex I) from Yarrowia lipolytica.

Complex I is the first and largest enzyme in the respiratory chain located in the inner mitochondrial membrane and in the membrane of many bacteria [1]. In the process of oxidizing NADH, Complex I translocates 4 protons across the membrane. This is followed by additional proton translocation by complexes III and IV. The resulting membrane potential powers ATP production by the F-ATPase. The minimal bacterial complex I contains 14 different subunits that are conserved throughout species. Eukaryotic complex I contains more than 26 additional (accessory) subunits. Complex I is L-shaped with a membrane arm and a peripheral arm that contains the NADH binding site and reaches into the mitochondrial matrix. The membrane arm contains 7 conserved subunits, ND1ND4,ND4L-ND6. ND2, ND4 and ND5 having sequence homology to certain antiporters [2] and are the putative subunits for active proton translocation [3]. Here we have analyzed the structure of a subcomplex of Y. lipolytica complex I, created by the deletion of the accessory subunit NB8M located in the membrane arm with a molecular mass of 11kDa. This resulted in the assembly of a subcomplex of molecular mass of approximately 680 kDa lacking the central subunits ND4, and ND5 [4].This complex showed reduced (30%) electron transfer activity and the stoichiometry of proton pumping was reduced by half.