A fatty acyl desaturase (fads2) with dual Δ6 and Δ5 activities from the freshwater carnivorous striped snakehead Channa striata

There is a lack of understanding on how the environment and trophic niche affect the capability of long-chain polyunsaturated fatty acids (LC-PUFA) in freshwater carnivorous teleost. In this present study, we isolated and functionally characterised a fatty acyl desaturase (Fads) from the striped snakehead Channa striata. Sequence comparison and phylogenetic analysis suggested a Fads2 protein that is closely related to previously characterised Fads2 proteins from freshwater carnivorous and marine herbivorous fish species. We further demonstrated the capacity of Delta 6 and Delta 5 desaturation activities for this particular desaturase, with highest activities towards the conversion of omega-3 (n-3) polyunsaturated fatty acids (PUFA). Low Delta 4 desaturation activity was also detected, although the significance of this at a physiological level remains to be studied. The expression of this striped snakehead Delta 6/Delta 5 fads2 gene was highest in brain, followed by liver and intestine. In liver, diet fortified with high LC-PUFA concentration impeded the expression of Delta 6/Delta 5 fads2 gene compared to vegetable oil (VO) based diets. The discovery of Delta 6/Delta 5 Fads2 desaturase here complements the previous discovery of a Delta 4 Fads2 desaturase and an Elov15 elongase, lending proof to the existence of all the required enzymatic machinery to biosynthesise LC-PUFA from C18 PUFA in a freshwater carnivorous species. (C) 2016 Elsevier Inc. All rights reserved.