Human Acyl-CoA Dehydrogenase-9 Plays a Novel Role in the Mitochondrial β-Oxidation of Unsaturated Fatty Acids

• Published in: The Journal of biological chemistry 2005-09, Vol.280 (37), p.32309-32316
• Main Authors: Ensenauer, Regina, He, Miao, Willard, Jan-Marie, Goetzman, Eric S., Corydon, Thomas J., Vandahl, Brian B., Mohsen, Al-Walid, Isaya, Grazia, Vockley, Jerry
• Format: Article
• Language: English
• Subjects: Acyl-CoA Dehydrogenase, Long-Chain - metabolism; Acyl-CoA Dehydrogenase, Long-Chain - physiology; Amino Acid Sequence; Animals; Brain - metabolism; Cell Membrane - metabolism; Chromatography, Gel; Chromatography, High Pressure Liquid; Cloning, Molecular; Escherichia coli; Escherichia coli - metabolism; Fatty Acids - metabolism; Humans; Kinetics; Lipid Metabolism; Lipids - chemistry; Mitochondria - metabolism; Models, Molecular; Molecular Sequence Data; Muscles - metabolism; Mutagenesis; Oxygen - metabolism; Peptides - chemistry; Polymerase Chain Reaction; Protein Conformation; Protein Structure, Tertiary; Recombinant Proteins - chemistry; Sequence Analysis, DNA; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Substrate Specificity; Transcription, Genetic
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M504460200

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 β-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 β-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.