Functional Characterization of the Duck and Turkey Fatty Acyl Elongase Enzymes ELOVL5 and ELOVL2

Abstract

In most Western countries, the consumption of fish is low and insufficient to provide the recommended daily intake of the n–3 (ω-3) long-chain polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA; 20:5n–3) and docosahexaenoic acid (DHA; 22:6n–3). Poultry has the potential to be a sustainable source of EPA and DHA if poultry species are capable of synthesizing these n–3 PUFAs from dietary plant-derived α-linolenic acid (ALA; 18:3n–3). In most animals, the elongation of very long-chain fatty acids (ELOVL) enzyme ELOVL2 is essential for conversion of dietary ALA to DHA because only ELOVL2 and not ELOVL5 can elongate docosapentaenoic acid (DPA; 22:5n–3) to 24:5n–3, the precursor of DHA. The chicken is the only poultry species in which elongase enzymes have been functionally characterized, and chicken ELOVL5 had unique DPA-to-24:5n–3 activity, which may enable chickens to synthesize more DHA than other animals. By using a yeast expression system, we examined the duck and turkey elongases, ELOVL2 and ELOVL5, to understand if all poultry species have similar potential to synthesize EPA and DHA. The duck and turkey ELOVL5 enzymes were active with C18–20 PUFAs only. The duck ELOVL2 had a broad substrate specificity with C18–22 PUFAs, whereas the turkey ELOVL2 was active only with EPA and C22 PUFAs. Both duck and turkey ELOVL2 enzymes catalyzed 2 rounds of EPA elongation, with the products being DPA and its elongation product, 24:5n–3. With exogenous DPA, both duck and turkey ELOVL2 synthesized 24:5n–3, with the duck ELOVL2 being more active than the turkey ELOVL2. The reason for the lack of DPA elongation activity by the duck and turkey ELOVL5 enzymes compared with the chicken ELOVL5 could not be elucidated by protein sequence comparisons. By using the elongase enzyme activities only as a predictor of DHA synthesis, ducks may have a similar ability to chickens to convert increasing dietary ALA to DHA.