Molecular analysis of the mechanisms underlying the biosynthesis of very long chain polyunsaturated fatty acids

极长链多不饱和脂肪酸（VLCPUFA）如花生四烯酸（20：4 n 6，ARA）、二十碳五烯酸（20：5 n-3，EPA）和二十二碳六烯酸（22：6 n 3，DHA）是哺乳动物细胞膜的必需组分和生物活性化合物如哺乳动物类二十烷酸和类二十二烷酸的前体。膳食VLCPUFA不仅可以预防常见的慢性疾病，如心血管疾病，代谢综合征和炎症性疾病，还可以增强眼睛，大脑和神经系统的性能。目前VLCPUFA补充剂的来源是来自鱼类和微生物的油。然而，鱼类数量的减少和鱼油中可能的污染物，沿着从微生物来源提取油的低产量和高成本，使得这些传统来源的经济可持续性受到质疑。在过去的几年里，研究人员已经探索了使用转基因植物作为VLCPUFA的替代来源。已经从微藻和真菌中鉴定出编码参与VLCPUFA生物合成的去饱和酶和延伸酶的基因，并成功地将其导入植物中。然而，表达这些基因的转基因植物产生的VLCPUFA水平远低于天然微生物中发现的水平，这意味着在异源系统中合成和积累更高水平的VLCPUFA需要除去饱和酶和延长酶本身之外的其他因子。本研究的目的是确定和表征这些因素在本地破囊壶菌属，一个单细胞原生生物能够积累大量的VLCPUFA在三酰甘油。具体而言，我们将确定和表征酰基转移酶，这有利于多不饱和酰基通量，和辅因子的缩合酶/延长酶，这有助于延长多不饱和脂肪酸。实现这些目标将大大有助于我们理解VLCPUFA合成、组装和积累的机制，并将为油料作物中VLCPUFA的转基因生产提供策略。

Very long chain polyunsaturated fatty acids (VLCPUFAs) such as arachidonic acid (20:4n 6, ARA), eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n 3, DHA) are essential components of mammalian cell membranes and precursors of biologically active compounds, such as mammalian eicosanoids and docosanoids. Dietary VLCPUFAs not only provide protection against common chronic diseases such as cardiovascular diseases, metabolic syndrome and inflammatory disorders, but can also enhance the performance of the eyes, brain and nervous system. The current sources for VLCPUFA supplements are oils from fish and microbes. However, shrinking fish populations and possible contaminants in fish oil, along with the low yields and high costs of oil extraction from microbial sources are making the economic sustainability of these traditional sources questionable. In the past few years, research workers have explored the use of transgenic plants as an alternative source for VLCPUFAs. Genes encoding desaturases and elongases involved in the biosynthesis of VLCPUFAs have been identified from microalgae and fungi, and successfully introduced into plants. However, transgenic plants expressing these genes produced VLCPUFAs at a level much lower than that found in native microorganisms, implying additional factors besides desaturases and elongases per se are required for the synthesis and accumulation of higher levels of VLCPUFAs in heterologous systems. The goal of this research is to identify and characterize these factors in the native Thraustochytrium sp, a single cellular protist capable of accumulating substantial amounts of VLCPUFAs in triacylglycerols. Specifically, we will identify and characterize acyltransferases, which facilitate polyunsaturated acyl flux, and cofactors of the condensing enzyme/elongase, which assist in the elongation of polyunsaturated fatty acids. Achieving these goals will significantly contribute to our understanding of the mechanisms underlying the synthesis, assembly and accumulation of VLCPUFAs, and will provide strategies for the transgenic production of VLCPUFAs in oilseed crops.