Abstract
Omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs) have important therapeutic and nutritional benefits in humans. In the biosynthesis pathways of these LC-PUFAs, omega-3 desaturase plays a critical role. In this study, we report a new omega-3 desaturase (PPD17) from Phytophthora parasitica. This desaturase shares high similarities with the known omega-3 desaturases and was expressed in Saccharomyces cerevisiae for the activity and substrate specificity research. The desaturase has a wide omega-6 fatty acid substrate, containing both 18C and 20C fatty acids, and exhibits a strong activity of delta-17 desaturase but a weak activity of delta-15 desaturase. The new desaturase converted the omega-6 arachidonic acid (AA, C20:4) to EPA (an omega-3 LC-PUFA, C20:5) with a substrate conversion rate of 70%. To obtain a high EPA-producing strain, we transformed PPD17 into Mortierella alpina, an AA-producing filamentous fungus. The EPA content of the total fatty acids in reconstruction strains reached 31.5% and was followed by the fermentation optimization of the EPA yield of up to 1.9 g/L. This research characterized a new omega-3 desaturase and provides a possibility of industrially producing EPA using M. alpina.
Highlights
Omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6), are critical for human health (Xue et al, 2013a)
DuPont assembled 30 copies of 9 different heterologous genes in Yarrowia lipolytica and the recombination strain accumulated 30% (w/w) lipids in biomass and EPA accounted for 56.6% (w/w) of the total fatty acids (TFAs; Xue et al, 2013b)
The sequence named PPD17 from P. parasitica searched from GenBank which is 1,086 bp and encodes a peptide of 361 amino acids was aligned with several known omega-3 desaturases using Clustal W (Figure 1A)
Summary
Omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6), are critical for human health (Xue et al, 2013a). Marine microorganisms and phytoplankton can de novo synthesize EPA and DHA, and these fatty acids are accumulated in marine fishes through the food chain (Xie et al, 2017). DuPont assembled 30 copies of 9 different heterologous genes in Yarrowia lipolytica and the recombination strain accumulated 30% (w/w) lipids in biomass and EPA accounted for 56.6% (w/w) of the total fatty acids (TFAs; Xue et al, 2013b). In contrast to the reconstitution of the EPA biosynthetic pathway in Y. lipolytica through the co-expression of a large number of heterologous genes, single-gene modification for EPA production in the microorganisms containing omega-3 LC-PUFA pathways could be simpler and more stable
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