title: Mitochondrial import and processing of wild type and type III mutant isovaleryl-CoA dehydrogenase.
abstract: Isovaleric acidemia is a rare inborn error of metabolism caused by a deficiency of isovaleryl-CoA dehydrogenase (IVD), a nucleus-encoded, homotetrameric, mitochondrial flavoenzyme that catalyzes the conversion of isovaleryl-CoA to 3-methylcrotonyl-CoA. We have previously identified a nucleotide deletion in the gene for IVD in fibroblasts from a patient with isovaleric acidemia leading to a shift in reading frame and premature termination of translation. The mutant IVD precursor is imported and processed to mature size, but no active enzyme is detected in mutant fibroblasts or expressed in Escherichia coli. Examination of the crystal structure of human IVD reveals that the C terminus is involved in tetramer stability. In vitro mitochondrial import experiments show that wild type IVD protein rapidly and stably forms mature homotetramer following import, whereas Type III mutant protein never forms stable oligomers. An additional series of mutant proteins with truncations and/or alterations in the C-terminal sequence implicates the C terminus of IVD in both enzyme activity and tetramer stability. Importantly, a dimeric intermediate in the folding pathway for wild type IVD has been identified in the in vitro mitochondrial import experiments, the first report of such an intermediate in the biogenesis of an acyl-CoA dehydrogenase.
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Volchenboum
authors.forename: J
authors.initials: J
authors.lastname: Vockley
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000592:Amino Acid Metabolism, Inborn Errors / Q000201:enzymology* / Q000235:genetics; D000595:Amino Acid Sequence; D001692:Biological Transport; D004795:Enzyme Stability; D045782:Hemiterpenes; D006801:Humans; D050769:Isovaleryl-CoA Dehydrogenase; D007930:Leucine / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010421:Pentanoic Acids / Q000378:metabolism; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid
chemical_list: D000214:Acyl Coenzyme A; D045782:Hemiterpenes; D010421:Pentanoic Acids; C008216:isovaleric acid; C017447:isovaleryl-coenzyme A; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D050769:Isovaleryl-CoA Dehydrogenase; D007930:Leucine