title: The alternative pathway C20 Delta8-desaturase from the non-photosynthetic organism Acanthamoeba castellanii is an atypical cytochrome b5-fusion desaturase.
abstract: A cDNA encoding a C20 Delta8-desaturase was isolated from the free-living soil amoeba, Acanthamoeba castellanii and functionally characterised by heterologous expression. The open reading frame of the A. castellanii C20 Delta8-desaturase showed similarity to other microsomal front-end desaturases, but the N-terminal domain contained a variant form of the conserved heme-binding motif in which H-P-G-G is replaced by H-P-A-G. Co-expression of the A. castellani Delta8-desaturase with the Isochrysis galbana Delta9-elongase in transgenic Arabidopsis plants confirmed the activity observed in yeast and its role in the alternative pathway for C20 polyunsaturated fatty acid synthesis. Acyl-CoA profiles of these transgenic plants revealed an unexpected accumulation of C20 fatty acids in the acyl-CoA pool. This is the first report of an alternative pathway C20 Delta8-desaturase from a non-photosynthetic organism, and also the first report of a front-end desaturase lacking the canonical cytochrome b5 domain.
authors.affiliation: Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.
authors.forename: Olga
authors.initials: O
authors.lastname: Sayanova
authors.forename: Richard
authors.initials: R
authors.lastname: Haslam
authors.forename: Baoxiu
authors.initials: B
authors.lastname: Qi
authors.forename: Colin M
authors.initials: CM
authors.lastname: Lazarus
authors.forename: Johnathan A
authors.initials: JA
authors.lastname: Napier
mesh_terms: D048248:Acanthamoeba castellanii / Q000201:enzymology*; D000214:Acyl Coenzyme A / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000201:enzymology; D015786:Cytochromes b5 / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000737:chemistry / Q000378:metabolism*; D015870:Gene Expression; D008969:Molecular Sequence Data; D010788:Photosynthesis; D010802:Phylogeny; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology
chemical_list: D000214:Acyl Coenzyme A; D011993:Recombinant Fusion Proteins; D015786:Cytochromes b5; D044943:Fatty Acid Desaturases; C119257:delta-8 fatty acid desaturase