Characterization and comparison of fatty acyl Δ6 desaturase cDNAs from freshwater and marine teleost fish species

Abstract

Abstract:Fish are the most important dietary source of the n-3 highly unsaturated fatty acids (HUFA), eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), that have particularly important roles in human nutrition reflecting their roles in critical physiological processes. The objective of the study described here was to clone, functionally characterise and compare expressed fatty acid desaturase genes involved in the production of EPA and DHA in freshwater and marine teleost fish species.Putative fatty acid desaturase cDNAs were isolated and cloned from common carp (Cyprinus carpio) and turbot (Psetta maximus). The enzymic activities of the products of these cDNAs, together with those of cDNAs previously cloned from rainbow trout (Oncorhynchus mykiss) and gilthead seabream (Sparus aurata), were determined by heterologous expression in the yeast containing the haem-binding motif, HPGG. Functional expression showed all four fish cDNAs encode basically unifunctional Δ6 fatty acid desaturase enzymes responsible for the first and ratelimiting step in the biosynthesis of HUFA from 18:3n-3 and 18:2n-6. All the fish desaturases were more active towards the n-3 substrate with 59.5%, 31.5%, 23.1% and 7.0% of 18:3n-3 being converted to 18:4n-3 in the case of turbot, trout, seabream and carp, respectively. The enzymes also showed very low, probably physiologically insignificant, levels of Δ5 desaturase activity, but none of the products showed Δ4 desaturase activity. The cloning and characterisation of desaturases from these fish is an important advance, as they are species in which there is a relative wealth of data on the nutritional regulation of fatty acid desaturation and HUFA synthesis, and between which substantive differences occur.

Physiological roles of fatty acyl desaturases and elongases in marine fish: Characterisation of cDNAs of fatty acyl Δ6 desaturase and elovl5 elongase of cobia (Rachycentron canadum)

“…The cobia Δ6 desaturase had greater activity with 18:3n-3 than 18:2n-6, which is consistent with all other fish Δ6 desaturases studied to date (Hastings et al, 2001;Zheng et al, 2004Zheng et al, , 2005Tocher et al, 2006). Early biochemical studies indicated that mammalian desaturases show an order of preference with n-3 > n-6 > n-9 (Brenner, 1974).…”

“…Evidence suggests that the dependence of marine fish on dietary HUFA is caused by a deficiency in the activity of one or more of the key enzymes in this pathway (Tocher, 2003). Fatty acyl desaturase cDNAs have been cloned from various fish species (Seiliez et al, 2001;Zheng et al, 2004), including a bifunctional Δ6/Δ5 desaturase from the freshwater zebrafish (Hastings et al, 2001) and separate, distinct Δ6 and Δ5 desaturases from Atlantic salmon (Hastings et al, 2005;Zheng et al, 2005). In contrast, only Δ6 desaturase cDNAs have so far been cloned from marine fish (Seiliez et al, 2003;Zheng et al, 2004;Tocher et al, 2006).…”

“…Fatty acyl desaturase cDNAs have been cloned from various fish species (Seiliez et al, 2001;Zheng et al, 2004), including a bifunctional Δ6/Δ5 desaturase from the freshwater zebrafish (Hastings et al, 2001) and separate, distinct Δ6 and Δ5 desaturases from Atlantic salmon (Hastings et al, 2005;Zheng et al, 2005). In contrast, only Δ6 desaturase cDNAs have so far been cloned from marine fish (Seiliez et al, 2003;Zheng et al, 2004;Tocher et al, 2006). Elongase cDNAs have been cloned from freshwater species, zebrafish, common carp and tilapia, salmonids, Atlantic salmon and rainbow trout, and marine species, Atlantic cod, turbot and gilthead sea bream (Agaba et al, 2004Hastings et al, 2005).…”

Environmental and dietary influences on highly unsaturated fatty acid biosynthesis and expression of fatty acyl desaturase and elongase genes in liver of Atlantic salmon (Salmo salar)

“…Recently, a variety of fatty acid desaturases and elongases, critical enzymes in the pathways for the biosynthesis of the long-chain C 20/22 HUFA from shorter chain C 18 PUFA, have been cloned from a range of freshwater and marine teleosts [8][9][10]. In particular, three cDNAs encoding enzymes in the HUFA biosynthetic pathway have been cloned from Atlantic salmon [11,12].…”

Molecular Cloning and Functional Characterisation of a Polyunsaturated Fatty Acid Elongase in a Marine Bivalve <i>Crassostrea</i><i> </i><i>angulata</i>

“…Significantly higher conversion rate was found with n-6 PUFA substrates than homologous n-3 substrates; however, in vertebrates, most of functionally characterized PUFA biosynthesis genes/enzymes show more activity toward n-3 PUFA substrates [32][33][34][35]. Marine microalgae enrich in n-3 series PUFAs [30], the oyster can obtain n-3 PUFAs by feeding these microalgae, this probably explains why the synthesizing ability of the n-3 series PUFAs became weaker than that of the n-6 series PUFAs.…”