出版社：American Society for Biochemistry and Molecular Biology
摘要：In algae, the biosynthesis of docosahexaenoic acid (22:6ω3; DHA) proceeds via the elongation of eicosapentaenoic acid (20:5ω3; EPA) to 22:5ω3, which is required as a substrate for the final Δ4 desaturation. To isolate the elongase specific for this step, we searched expressed sequence tag and genomic databases from the algae Ostreococcus tauri and Thalassiosira pseudonana , from the fish Oncorhynchus mykiss , from the frog Xenopus laevis , and from the sea squirt Ciona intestinalis using as a query the elongase sequence PpPSE1 from the moss Physcomitrella patens . The open reading frames of the identified elongase candidates were expressed in yeast for functional characterization. By this, we identified two types of elongases from O. tauri and T. pseudonana : one specific for the elongation of (Δ6-)C18-PUFAs and one specific for (Δ5-)C20-PUFAs, showing highest activity with EPA. The clones isolated from O. mykiss , X. laevis , and C. intestinalis accepted both C18- and C20-PUFAs. By coexpression of the Δ6- and Δ5-elongases from T. pseudonana and O. tauri , respectively, with the Δ5- and Δ4-desaturases from two other algae we successfully implemented DHA synthesis in stearidonic acid-fed yeast. This may be considered an encouraging first step in future efforts to implement this biosynthetic sequence into transgenic oilseed crops.
