Thraustochytrium is a unicellular marine protist for the commercial production of very long‐chain polyunsaturated fatty acids (VLCPUFAs). Biosynthesis of these VLCPUFAs in the protist is catalysed by a PUFA synthase comprising three subunits, each with multiple catalytic domains. Among these domains, two tandem FabA‐like dehydratase domains (DH1 and DH2) in subunit‐C together are responsible for introducing double bonds in VLCPUFAs. Domain swapping analysis in yeast showed that the defective phenotype of a Scfas1 mutant could be complemented by expressing an engineered ScFAS1 gene in which the DH domain was replaced by a single DH1 or mutated DH2 of the two. Heterologous expression of the PUFA synthase in E. coli showed that the mutation of DH1 of the two or deletion of DH1 or substitution of DH1 with DH2 resulted in the complete loss of activity in the biosynthesis of VLCPUFAs. Mutation of DH2 of the two or deletion of the DH2 domain produced a small amount of DPA, but not docosahexaenoic acid (DHA). These results indicate that each of the two FabA‐like domains of the PUFA synthase possesses distinct function. DH1 domain is essential for the biosynthesis of VLCPUFAs, but DH2 domain is required for the biosynthesis of DHA.

中文翻译：

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在非常长链的多不饱和脂肪酸的生物合成中，两个多不饱和脂肪酸合酶的FabA样脱水酶结构域的不同功能。

破囊壶菌是单细胞海洋生物，非常商业化生产长链多不饱和脂肪酸（VLCPUFAs）。这些VLCPUFA在原生生物中的生物合成由包含三个亚基的PUFA合酶催化，每个亚基均具有多个催化域。在这些域中，亚基C中的两个串联的FabA样脱水酶域（DH1和DH2）共同负责在VLCPUFA中引入双键。酵母中的结构域交换分析表明，Scfas1突变体的缺陷表型可以通过表达工程化的ScFAS1基因（其中DH结构域被单个DH1或两个突变的DH2代替）来补充。所述PUFA的异源表达在合酶ë。大肠杆菌结果表明，DH1的两个突变或DH1的缺失或DH1被DH2取代导致VLCPUFAs生物合成中的活性完全丧失。DH2的两个突变或DH2结构域的缺失产生了少量的DPA，但没有二十二碳六烯酸（DHA）。这些结果表明，PUFA合酶的两个FabA类结构域中的每一个都具有独特的功能。DH1结构域对于VLCPUFAs的生物合成至关重要，但是DH2结构域对于DHA的生物合成而言是必需的。