Martins-Noguerol R, DeAndrés-Gil C, Garcés R, Salas J J, Martínez-Force E, Moreno-Pérez A J
Group of Genetics and Biochemistry of Seed Lipids, Department of Biochemistry and Molecular Biology of Plants Products, Instituto de la Grasa (CSIC), Ctra. de Utrera km 1, Building 46, 41013 Sevilla, Spain.
Heliyon. 2020 Oct 15;6(10):e05237. doi: 10.1016/j.heliyon.2020.e05237. eCollection 2020 Oct.
is a deciduous tree, popular in temperate regions for its ornamental value, which accumulates unusual cyanolipids in its seeds. The seed oil of this plant is rich in the unusual cis-11-eicosenoic fatty acid (20:1, or gondoic acid), a monounsaturated oil of interest to the oleochemical industry. In higher plants, de novo fatty acid biosynthesis takes place in the plastids, a process that is terminated by hydrolysis of the thioester bond between the acyl moiety and the ACP by acyl-ACP thioesterases. The specificity of acyl-ACP thioesterases is fundamental in controlling the fatty acid composition of seed oil. To determine the mechanisms involved in fatty acid biosynthesis in seeds, we isolated, cloned and sequenced two cDNAs encoding acyl-ACP thioesterases in this plant, FatA and FatB. Both of them were expressed heterologously in and characterized with different acyl-ACP substrates. The FatB2 displayed unusual substrate specificity, so that unlike most FatB2 type enzymes, it displayed preference for oleoyl-ACP instead of palmitoyl-ACP. This specificity was consistent with the changes in and fatty acid composition following heterologous expression of this enzyme. FatB also showed certain genetic divergence relative to other FatB-type thioesterases and when modelled, its structure revealed differences at the active site. Together, these results suggest that this thioesterase could be a new class of FatB not described previously.
是一种落叶乔木，因其观赏价值在温带地区广受欢迎，其种子中积累了不寻常的氰脂。这种植物的种子油富含不寻常的顺式-11-二十碳烯酸（20:1，即贡多酸），这是一种对油脂化学工业有意义的单不饱和油。在高等植物中，从头脂肪酸生物合成发生在质体中，该过程通过酰基-ACP硫酯酶水解酰基部分与ACP之间的硫酯键而终止。酰基-ACP硫酯酶的特异性对于控制种子油的脂肪酸组成至关重要。为了确定种子中脂肪酸生物合成所涉及的机制，我们分离、克隆并测序了该植物中编码酰基-ACP硫酯酶的两个cDNA，即FatA和FatB。它们都在异源系统中表达，并用不同的酰基-ACP底物进行了表征。其中的FatB2表现出不寻常的底物特异性，因此与大多数FatB2型酶不同，它对油酰-ACP而不是棕榈酰-ACP表现出偏好。这种特异性与该酶异源表达后脂肪酸组成的变化一致。FatB相对于其他FatB型硫酯酶也表现出一定的遗传差异，并且在进行建模时，其结构在活性位点处显示出差异。综合这些结果表明，这种硫酯酶可能是一类以前未描述过的新型FatB。
