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

超长链多不饱和脂肪酸(VLCPUFAs)，如花生四烯酸(20：4N6，ARA)、二十碳五烯酸(20：5N-3，EPA)和二十二碳六烯酸(22：6N3，DHA)是哺乳动物细胞膜的重要组成部分，也是生物活性化合物的前体，如哺乳动物二十烷类化合物和二十二碳二烯类化合物。膳食中的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、大脑和神经系统的表现。目前VLCPUFA补充剂的来源是鱼油和微生物。然而，鱼类数量的减少和鱼油中可能的污染物，以及从微生物来源提取石油的产量低和成本高，使这些传统来源的经济可持续性受到质疑。在过去的几年里，研究人员探索了使用转基因植物作为VLCPUFAs的替代来源。编码与VLCPUFAs生物合成有关的去饱和酶和伸长酶的基因已经从微藻和真菌中鉴定出来，并成功地导入植物。然而，表达这些基因的转基因植物产生的VLCPUFAs水平远远低于在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VLCPUFAs需要除脱饱和酶和伸长酶本身之外的额外因素。这项研究的目的是在天然的Thraustochytrium sp中鉴定和表征这些因素，Thraustochytrium sp是一种能够在三酰甘油中积累大量VLCPUFA的单一细胞原生生物。具体地说，我们将识别和表征促进多不饱和酰基流动的酰基转移酶，以及有助于多不饱和脂肪酸延伸的缩合酶/伸长酶的辅因子。实现这些目标将有助于我们理解VLCPUFAs合成、组装和积累的机制，并将为在油料作物中转基因生产VLCPUFAs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.