Two novel thioesterases are key determinants of the bimodal distribution of acyl chain length of Cuphea palustris seed oil
Two novel thioesterases are key determinants of the bimodal distribution of acyl chain length of Cuphea palustris seed oil
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DOI：
10.1104/pp.110.1.203
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发表时间：
1996-01-01
期刊：
影响因子：
7.4
通讯作者：
Fillatti, J
中科院分区：
文献类型：
--
作者：
Dehesh, K;Edwards, P;Fillatti, J
Cuphea palustris的籽油具有不同寻常的脂肪酰基组成，其中主要的脂肪酰基，肉豆蔻酸酯（64%）和辛酸酯（20%），相差超过两个亚甲基。我们从C. palustris中分离出两个硫酯酶（TE） cdna，编码Cp FatB1和Cp FatB2蛋白，它们在大肠杆菌中表达时，分别对8:0/10:0-和14:0/16:0-酰基载体蛋白底物具有TE活性。重组亲和纯化酶的特异性活性表明，Cp FatB2在动力学上优于Cp FatB1。这一结果与种子油中14:0的优势一致，尽管两种转录本在种子中的mRNA丰度明显相等。在palustris中，这两个序列的表达仅限于种子组织。基于这些研究结果，我们认为这两种酶是决定石竹油双峰链长组成的主要因素。通过反相高效液相色谱法对未成熟和成熟种子油进行分析，证实主甘油三酯的含量分别为8:0和14:0。这一结果表明，这两种脂肪酸在油脂沉积的所有发育阶段都是在同一时间和同一细胞中合成的，表明这两种脂肪酸在同一脂肪酸合成系统中共同作用。
The seed oil of Cuphea palustris has an unusual fatty-acyl composition, whereby the principal fatty-acyl groups, myristate (64%) and caprylate (20%), differ by more than two methylenes. We have isolated two thioesterase (TE) cDNAs from C. palustris, encoding proteins designated Cp FatB1 and Cp FatB2, which, when expressed in Escherichia coli, have TE activities specific for 8:0/10:0- and 14:0/16:0-acyl carrier protein substrates, respectively. The specific activities of the recombinant affinity-purified enzymes indicate that Cp FatB2 is kinetically superior to Cp FatB1. This result is consistent with the predominance of 14:0 in the seed oil, despite apparently equal mRNA abundance of the two transcripts in the seed. In C. palustris the expression of both sequences is confined to the seed tissues. Based on these findings we propose that these two enzymes are major factors determining the bimodal chain-length composition of C. palustris oil. Analysis of the immature and mature seed oil by reverse-phase high-performance liquid chromatography confirmed that the principal triglycerides contain both 8:0 and 14:0. This result indicates that both fatty acids are synthesized at the same time and in the same cells at all developmental stages during oil deposition, suggesting that the two ifs act together in the same fatty acid synthesis system.