title: Human acyl-CoA dehydrogenase-9 plays a novel role in the mitochondrial beta-oxidation of unsaturated fatty acids.
abstract: Unsaturated fatty acids play an important role in the prevention of human diseases such as diabetes, obesity, cancer, and neurodegeneration. However, their oxidation in vivo by acyl-CoA dehydrogenases (ACADs) that catalyze the first step of each cycle of mitochondrial fatty acid beta-oxidation is not entirely understood. Recently, a novel ACAD (ACAD-9) of unknown function that is highly homologous to human very-long-chain acyl-CoA dehydrogenase was identified by large-scale random sequencing. To characterize its enzymatic role, we have expressed ACAD-9 in Escherichia coli, purified it, and determined its pattern of substrate utilization. The N terminus of the mature form of the enzyme was identified by in vitro mitochondrial import studies of precursor protein. A 37-amino acid leader peptide was cleaved sequentially by two mitochondrial peptidases to yield a predicted molecular mass of 65 kDa for the mature subunit. Submitochondrial fractionation studies found native ACAD-9 to be associated with the mitochondrial membrane. Gel filtration analysis indicated that, like very-long-chain acyl-CoA dehydrogenase, ACAD-9 is a dimer, in contrast to the other known ACADs, which are tetramers. Purified mature ACAD-9 had maximal activity with long-chain unsaturated acyl-CoAs as substrates (C16:1-, C18:1-, C18:2-, C22:6-CoA). These results suggest a previously unrecognized role for ACAD-9 in the mitochondrial beta-oxidation of long-chain unsaturated fatty acids. Because of the substrate specificity and abundance of ACAD-9 in brain, we speculate that it may play a role in the turnover of lipid membrane unsaturated fatty acids that are essential for membrane integrity and structure.
authors: Department of Medical Genetics, Pediatric and Adolescent Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
authors: Regina
authors: R
authors: Ensenauer
authors: Miao
authors: M
authors: He
authors: Jan-Marie
authors: JM
authors: Willard
authors: Eric S
authors: ES
authors: Goetzman
authors: Thomas J
authors: TJ
authors: Corydon
authors: Brian B
authors: BB
authors: Vandahl
authors: Al-Walid
authors: AW
authors: Mohsen
authors: Grazia
authors: G
authors: Isaya
authors: Jerry
authors: J
authors: Vockley
mesh_terms: D044942:Acyl-CoA Dehydrogenase, Long-Chain / Q000378:metabolism / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008928:Mitochondria / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism; D016296:Mutagenesis; D010100:Oxygen / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017422:Sequence Analysis, DNA; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013379:Substrate Specificity; D014158:Transcription, Genetic
chemical_list: D005227:Fatty Acids; D008055:Lipids; D010455:Peptides; D011994:Recombinant Proteins; D044942:Acyl-CoA Dehydrogenase, Long-Chain; C467805:ACADVL protein, human; D010100:Oxygen