Control Mechanism for cis Double-Bond Formation by Polyunsaturated Fatty-Acid Synthases
Control Mechanism for cis Double-Bond Formation by Polyunsaturated Fatty-Acid Synthases
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DOI：
10.1002/anie.201812623
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发表时间：
2019-02-18
影响因子：
16.6
通讯作者：
Dairi, Tohru
中科院分区：
文献类型：
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作者：
Hayashi, Shohei;Satoh, Yasuharu;Dairi, Tohru
多不饱和脂肪酸（PUFA）如二十二碳六烯酸（DHA）、二十碳五烯酸（EPA）和花生四烯酸（ARA）是人类必需的脂肪酸。一些微生物通过由具有多个催化结构域的四个亚基组成的PUFA酶来生物合成这些PUFA。这些PUFA酶各自产生特定的PUFA而没有不期望的副产物，即使每个大亚基中的多个催化结构域非常相似。然而，详细的生物合成途径和机制，控制最终产品的档案仍然是模糊的。在这项研究中，在ARA合成酶的C-亚基中的FabA型脱氢酶结构域（DHFabA）和B-亚基中的聚酮脱氢酶型脱氢酶结构域（DHPKS）被揭示为ARA生物合成所必需的体内基因交换试验。此外，用截短的重组酶和C-4-至C-8-酰基ACP底物的体外分析表明，ARA和EPA脱氢酶利用两种类型的DH结构域DHPKS和DHFabA，这取决于碳链长度，以将饱和或顺式双键引入到生长的酰基链。
Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final-product profiles are still obscure. In this study, the FabA-type dehydratase domain (DHFabA) in the C-subunit and the polyketide synthase-type dehydratase domain (DHPKS) in the B-subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C-4- to C-8-acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DHPKS and DHFabA, depending on the carbon-chain length, to introduce either saturation or cis double bonds to growing acyl chains.