Broad-range and binary-range acyl-acyl-carrier-protein thioesterases suggest an alternative mechanism for medium-chain production in seeds

• Published in: Plant physiology (Bethesda) 1997-06, Vol.114 (2), p.669-677
• Main Authors: Voelker, T.A. (Calgene, Inc., Davis, CA.), Jones, A, Cranmer, A.M, Davies, H.M, Knutzon, D.S
• Format: Article
• Language: English
• Subjects: ACIDE GRAS; ACIDOS GRASOS; ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; ADN; Amino Acid Sequence; AMINO ACID SEQUENCES; BINDING PROTEINS; Biochemistry and Enzymology; Biological and medical sciences; BIOSINTESIS; BIOSYNTHESE; BIOSYNTHESIS; CHEMICAL COMPOSITION; CLONACION; CLONAGE; CLONING; COMPLEMENTARY DNA; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; CULTURE MEDIA; DNA; DNA, Complementary - genetics; Enzymes; ENZYMIC ACTIVITY; Escherichia coli - genetics; ESTERASAS; ESTERASE; ESTERASES; FATTY ACIDS; Fatty Acids - biosynthesis; Fundamental and applied biological sciences. Psychology; Gene Library; Genetic Engineering; GENETIC REGULATION; GENETICA; GENETICS; GENETIQUE; GRAINE; Hydrolysis; Lipids; MEDIO DE CULTIVO; MEDIUM CHAIN FATTY ACIDS; Metabolism; MILIEU DE CULTURE; MOLECULAR SEQUENCE DATA; MYRISTICA FRAGRANS; Nonesterified fatty acids; Nutmeg; Plant physiology and development; Plant Proteins - genetics; Plant Proteins - metabolism; PROTEINAS AGLUTINANTES; PROTEINE DE LIAISON; Proteins; Recombinant Proteins - metabolism; RNA; SEEDS; Seeds - enzymology; SEMILLA; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Species Specificity; Spices; Substrate Specificity; SUBSTRATES; Thiolester Hydrolases - genetics; Thiolester Hydrolases - metabolism; Trees - enzymology; Trees - genetics; ULMUS AMERICANA
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.114.2.669

In the current model of medium-chain (C8-14) fatty acid biosynthesis in seeds, specialized FatB acyl-acyl-carrier-protein (ACP) thioesterases are responsible for the production of medium chains. We have isolated and characterized Fat8 cDNAs from the maturing seeds of elm (Ulmus americana) and nutmeg (Myristica fragrans), which accumulate predominantly caprate (10:0)- and myristate (14:0)-containing oils, respectively. In neither species were we able to find cDNAs encoding enzymes specialized for these chain lengths. Nutmeg FatB hydrolyses C14-18 substrates in vitro and expression in Brassica napus seeds leads to an oil enriched in C14-18 saturates. Elm FatB1 displays a binary specificity: one activity is centered on 10:0-ACP, and a second is centered on palmitate (16:0)-ACP After expression in B. napus seeds the oil is enriched in C10-18 saturates, predominantly 16:0, 14:0, and 10:0. The composition of free fatty acids produced by elm FatB1 in Escherichia coli shifts from C14-16 to mostly C8-10 by increasing the rate of chain termination by this enzyme. These results suggest the existence of an alternative mechanism used in the evolution of medium-chain production, a model of which is presented