title: Characterization of a structurally and functionally diverged acyl-acyl carrier protein desaturase from milkweed seed.
abstract: A cDNA for a structurally variant acyl-acyl carrier protein (ACP) desaturase was isolated from milkweed (Asclepias syriaca) seed, a tissue enriched in palmitoleic (16:1delta9)* and cis-vaccenic (18:1delta11) acids. Extracts of Escherichia coli that express the milkweed cDNA catalyzed delta9 desaturation of acyl-ACP substrates, and the recombinant enzyme exhibited seven- to ten-fold greater specificity for palmitoyl (16:0)-ACP and 30-fold greater specificity for myristoyl (14:0)-ACP than did known delta9-stearoyl (18:0)-ACP desaturases. Like other variant acyl-ACP desaturases reported to date, the milkweed enzyme contains fewer amino acids near its N-terminus compared to previously characterized delta9-18:0-ACP desaturases. Based on the activity of an N-terminal deletion mutant of a delta9-18:0-ACP desaturase, this structural feature likely does not account for differences in substrate specificities.
authors.affiliation: Biology Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: E B
authors.initials: EB
authors.lastname: Cahoon
authors.forename: S J
authors.initials: SJ
authors.lastname: Coughlan
authors.forename: J
authors.initials: J
authors.lastname: Shanklin
mesh_terms: D000213:Acyl Carrier Protein / Q000378:metabolism*; D000595:Amino Acid Sequence; D018076:DNA, Complementary / Q000032:analysis; D018744:DNA, Plant / Q000032:analysis; D004926:Escherichia coli / Q000235:genetics; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010944:Plants / Q000201:enzymology*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012639:Seeds / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D000213:Acyl Carrier Protein; D018076:DNA, Complementary; D018744:DNA, Plant; D005229:Fatty Acids, Monounsaturated; D011993:Recombinant Fusion Proteins; C008757:palmitoleic acid; D006899:Mixed Function Oxygenases; C018747:acyl-(acyl-carrier-protein)desaturase; C054211:9-tetradecenoic acid