Institute of Aquaculture, Faculty of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK.
Department of Biological Sciences, University of Abuja, P.M.B. 117, Abuja, Nigeria.
Sci Rep. 2017 Jun 20;7(1):3889. doi: 10.1038/s41598-017-04288-2.
Docosahexaenoic acid (DHA) plays important physiological roles in vertebrates. Studies in rats and rainbow trout confirmed that DHA biosynthesis proceeds through the so-called "Sprecher pathway", a biosynthetic process requiring a Δ6 desaturation of 24:5n-3 to 24:6n-3. Alternatively, some teleosts possess fatty acyl desaturases 2 (Fads2) that enable them to biosynthesis DHA through a more direct route termed the "Δ4 pathway". In order to elucidate the prevalence of both pathways among teleosts, we investigated the Δ6 ability towards C substrates of Fads2 from fish with different evolutionary and ecological backgrounds. Subsequently, we retrieved public databases to identify Fads2 containing the YXXN domain responsible for the Δ4 desaturase function, and consequently enabling these species to operate the Δ4 pathway. We demonstrated that, with the exception of Δ4 desaturases, fish Fads2 have the ability to operate as Δ6 desaturases towards C PUFA enabling them to synthesise DHA through the Sprecher pathway. Nevertheless, the Δ4 pathway represents an alternative route in some teleosts and we identified the presence of putative Δ4 Fads2 in a further 11 species and confirmed the function as Δ4 desaturases of Fads2 from medaka and Nile tilapia. Our results demonstrated that two alternative pathways for DHA biosynthesis exist in teleosts.
二十二碳六烯酸 (DHA) 在脊椎动物中发挥着重要的生理作用。在大鼠和虹鳟中的研究证实，DHA 的生物合成是通过所谓的“Sprecher 途径”进行的，这是一个需要将 24:5n-3 进行 Δ6 去饱和化生成 24:6n-3 的生物合成过程。然而，一些硬骨鱼具有脂肪酸去饱和酶 2 (Fads2)，使它们能够通过一种更直接的途径，即“Δ4 途径”，来合成 DHA。为了阐明这两种途径在硬骨鱼中的普遍性，我们研究了具有不同进化和生态背景的鱼类 Fads2 对 C 底物的 Δ6 能力。随后，我们检索了公共数据库，以鉴定含有 YXXN 结构域的 Fads2，该结构域负责 Δ4 去饱和酶的功能，从而使这些物种能够进行 Δ4 途径。我们证明，除了 Δ4 去饱和酶外，鱼类 Fads2 具有作为 Δ6 去饱和酶对 C 类 PUFA 的能力，使它们能够通过 Sprecher 途径合成 DHA。然而，在一些硬骨鱼中，Δ4 途径代表了一种替代途径，我们在另外 11 个物种中发现了潜在的 Δ4 Fads2，并证实了来自 medaka 和尼罗罗非鱼的 Fads2 作为 Δ4 去饱和酶的功能。我们的研究结果表明，两种替代的 DHA 生物合成途径存在于硬骨鱼中。
