title: Identification of a cDNA encoding a novel C18-Delta(9) polyunsaturated fatty acid-specific elongating activity from the docosahexaenoic acid (DHA)-producing microalga, Isochrysis galbana.
abstract: Isochrysis galbana, a marine prymnesiophyte microalga, is rich in long chain polyunsaturated fatty acids such as docosahexaenoic acid (C22:6n-3, Delta(4,7,10,13,16,19)). We used a polymerase chain reaction-based strategy to isolate a cDNA, designated IgASE1, encoding a polyunsaturated fatty acid-elongating activity from I. galbana. The coding region of 263 amino acids predicts a protein of 30 kDa that shares only limited homology to animal and fungal proteins with elongating activity. Functional analysis of IgASE1, by expression in Saccharomyces cerevisiae, was used to determine its activity and substrate specificity. Transformed yeast cells specifically elongated the C18-Delta(9) polyunsaturated fatty acids, linoleic acid (C18:2n-6, Delta(9,12)) and alpha-linolenic acid (C18:3n-3, Delta(9,12,15)), to eicosadienoic acid (C20:2n-6, Delta(11,14)) and eicosatrienoic acid (C20:3n-3, Delta(11,14,17)), respectively. To our knowledge this is the first time such an elongating activity has been functionally characterised. The results also suggest that a major route for eicosapentaenoic acid (C20:5n-3, Delta(5,8,11,14,17)) and docosahexaenoic acid syntheses in I. galbana may involve a Delta(8) desaturation pathway.
authors.affiliation: School of Biological Sciences, University of Bristol, UK.
authors.forename: Baoxiu
authors.initials: B
authors.lastname: Qi
authors.forename: Frédéric
authors.initials: F
authors.lastname: Beaudoin
authors.forename: Tom
authors.initials: T
authors.lastname: Fraser
authors.forename: A Keith
authors.initials: AK
authors.lastname: Stobart
authors.forename: Johnathan A
authors.initials: JA
authors.lastname: Napier
authors.forename: Colin M
authors.initials: CM
authors.lastname: Lazarus
mesh_terms: D000123:Acetyltransferases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D002849:Chromatography, Gas; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics* / Q000302:isolation & purification; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D056890:Eukaryota / Q000378:metabolism*; D000081031:Fatty Acid Elongases; D005231:Fatty Acids, Unsaturated / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D018076:DNA, Complementary; D005231:Fatty Acids, Unsaturated; D004281:Docosahexaenoic Acids; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases