title: Subunit NDUFV3 is present in two distinct isoforms in mammalian complex I.
abstract: Complex I (NADH:ubiquinone oxidoreductase) is the first enzyme of the electron transport chain in mammalian mitochondria. Extensive proteomic and structural analyses of complex I from Bos taurus heart mitochondria have shown it comprises 45 subunits encoded on both the nuclear and mitochondrial genomes; 44 of them are different and one is present in two copies. The bovine heart enzyme has provided a model for studying the composition of complex I in other mammalian species, including humans, but the possibility of additional subunits or isoforms in other species or tissues has not been explored. Here, we describe characterization of the complexes I purified from five rat tissues and from a rat hepatoma cell line. We identify a~50kDa isoform of subunit NDUFV3, for which the canonical isoform is only ~10kDa in size. We combine LC-MS and MALDI-TOF mass spectrometry data from two different purification methods (chromatography and immuno-purification) with information from blue native PAGE analyses to show the long isoform is present in the mature complex, but at substoichiometric levels. It is also present in complex I in cultured human cells. We describe evidence that the long isoform is more abundant in both the mitochondria and purified complexes from brain (relative to in heart, liver, kidney and skeletal muscle) and more abundant still in complex I in cultured cells. We propose that the long 50kDa isoform competes with its canonical 10kDa counterpart for a common binding site on the flavoprotein domain of complex I.
authors.affiliation: The Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, U. K.
authors.forename: Hannah R
authors.initials: HR
authors.lastname: Bridges
authors.affiliation: The Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, U. K.
authors.forename: Khairunnisa
authors.initials: K
authors.lastname: Mohammed
authors.affiliation: The Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, U. K.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Harbour
authors.affiliation: The Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, U. K.. Electronic address: jh@mrc-mbu.cam.ac.uk.
authors.forename: Judy
authors.initials: J
authors.lastname: Hirst
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D042967:Electron Transport Complex I / Q000737:chemistry / Q000191:economics / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics*; D008929:Mitochondria, Heart / Q000737:chemistry / Q000235:genetics; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D051381:Rats
chemical_list: D045342:Light-Harvesting Protein Complexes; C000619120:NDUFV3 protein, human; C000621253:NDUFV3 protein, rat; D020033:Protein Isoforms; D042967:Electron Transport Complex I
keywords: Complex I; NADH:ubiquinone oxidoreductase; NDUFV3; isoform; mitochondria; rat