title: Cloning, expression, and characterization of the human mitochondrial beta-ketoacyl synthase. Complementation of the yeast CEM1 knock-out strain.
abstract: A human beta-ketoacyl synthase implicated in a mitochondrial pathway for fatty acid synthesis has been identified, cloned, expressed, and characterized. Sequence analysis indicates that the protein is more closely related to freestanding counterparts found in prokaryotes and chloroplasts than it is to the beta-ketoacyl synthase domain of the human cytosolic fatty acid synthase. The full-length nuclear-encoded 459-residue protein includes an N-terminal sequence element of approximately 38 residues that functions as a mitochondrial targeting sequence. The enzyme can elongate acyl-chains containing 2-14 carbon atoms with malonyl moieties attached in thioester linkage to the human mitochondrial acyl carrier protein and is able to restore growth to the respiratory-deficient yeast mutant cem1 that lacks the endogenous mitochondrial beta-ketoacyl synthase and exhibits lowered lipoic acid levels. To date, four components of a putative type II mitochondrial fatty acid synthase pathway have been identified in humans: acyl carrier protein, malonyl transferase, beta-ketoacyl synthase, and enoyl reductase. The substrate specificity and complementation data for the beta-ketoacyl synthase suggest that, as in plants and fungi, in humans this pathway may play an important role in the generation of octanoyl-acyl carrier protein, the lipoic acid precursor, as well as longer chain fatty acids that are required for optimal mitochondrial function.
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, California 94609, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Anil K
authors.initials: AK
authors.lastname: Joshi
authors.forename: Jörg
authors.initials: J
authors.lastname: Hofmann
authors.forename: Eckhart
authors.initials: E
authors.lastname: Schweizer
authors.forename: Stuart
authors.initials: S
authors.lastname: Smith
mesh_terms: D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002569:Cerulenin / Q000737:chemistry; D003001:Cloning, Molecular; D017931:DNA Primers / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004952:Esters / Q000737:chemistry; D005816:Genetic Complementation Test; D006801:Humans; D007700:Kinetics; D013058:Mass Spectrometry; D051379:Mice; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D008063:Thioctic Acid / Q000737:chemistry; D014018:Tissue Distribution
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D004952:Esters; D002569:Cerulenin; D008063:Thioctic Acid; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase