title: Beta-ketoacyl-acyl carrier protein synthase IV: a key enzyme for regulation of medium-chain fatty acid synthesis in Cuphea lanceolata seeds.
abstract: With the aim of elucidating the mechanisms involved in the biosynthesis of medium-chain fatty acids in Cuphea lanceolata Ait., a crop accumulating up to 90% decanoic acid in seed triacylglycerols, cDNA clones of a beta-ketoacyl-acyl carrier protein (ACP) synthase IV (clKAS IV, EC 2.3.1.41) were isolated from C. lanceolata seed embryos. The amino acid sequence deduced from clKAS IV cDNA showed 80% identity to other plant KAS II-type enzymes, 55% identity towards plant KAS I and over 90% towards other Cuphea KAS IV-type sequences. Recombinant clKAS IV was functionally overexpressed in Escherichia coli, and substrate specificity of purified enzyme showed strong preference for elongation of short-chain and medium-chain acyl-ACPs (C4- to C10-ACP) with nearly equal activity. Further elongation steps were catalysed with distinctly less activity. Moreover, short- and medium-chain acyl-ACPs exerted a chain-length-specific and concentration-dependent substrate inhibition of clKAS IV. Based on these findings a regulatory mechanism for medium-chain fatty acid synthesis in C. lanceolata is presented.
authors.affiliation: Institut für Biochemie, Universitat Munster, Wilhelm-Klemm-Str. 2, Germany.
authors.forename: Burkhardt Siegfried
authors.initials: BS
authors.lastname: Schütt
authors.forename: Amine
authors.initials: A
authors.lastname: Abbadi
authors.forename: Brigitte
authors.initials: B
authors.lastname: Loddenkötter
authors.forename: Monika
authors.initials: M
authors.lastname: Brummel
authors.forename: Friedrich
authors.initials: F
authors.lastname: Spener
mesh_terms: D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D031562:Cuphea / Q000201:enzymology* / Q000235:genetics; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005227:Fatty Acids / Q000096:biosynthesis*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D012639:Seeds / Q000201:enzymology* / Q000235:genetics; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity
chemical_list: D018076:DNA, Complementary; D005227:Fatty Acids; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase