Carbocyclic fatty acids in plants:: Biochemical and molecular genetic characterization of cyclopropane fatty acid synthesis of Sterculia foetida
Carbocyclic fatty acids in plants:: Biochemical and molecular genetic characterization of cyclopropane fatty acid synthesis of Sterculia foetida
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DOI：
10.1073/pnas.092152999
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发表时间：
2002-05-14
影响因子：
11.1
通讯作者：
Ohlrogge, J
中科院分区：
文献类型：
--
作者：
Bao, XM;Katz, S;Ohlrogge, J
含有三个碳环的脂肪酸存在于细菌和植物中。细菌合成环丙烷脂肪酸（CPA-FAs）仅通过将S-腺苷甲硫氨酸的亚甲基添加到单烯磷脂结合脂肪酸的顺式双键上。在植物中，CPA-FAs通常是次要组分，环丙烯脂肪酸（CPE-FAs）更丰富。胖大海籽油含有65-78%的CPE-FA，主要是胖大海酸。为了解决植物中碳环脂肪酸的合成，从发育中的种子在最大油沉积期间构建cDNA文库。在5,300个表达的序列标签中，约0.4%来自一个基因，该基因与细菌CPA-FA合酶具有相似性。然而，预测的蛋白质是两倍大的细菌同源物，并代表一个融合的FAD-含有氧化酶在N端和甲基转移酶在C端。在烟草悬浮细胞中对分离的全长cDNA进行了功能分析，其表达导致总脂肪酸中高达6.2%的二氢脂肪酸的积累。此外，在转基因烟草细胞中，二氢睾酮被[甲基-C-14]蛋氨酸和[C-14]油酸特异性标记。体外测定S. foetida种子提取物，5-腺苷甲硫氨酸作为亚甲基供体用于从油酸酯合成二氢甾醇酯。在这两个系统中，二氢睾酮主要积累在磷脂酰胆碱中。总之，从S.高等植物中产生碳环脂肪酸的途径被定义为通过C1单元的转移，最可能是从S-腺苷甲硫氨酸转移到油酸酯。
Fatty acids containing three-member carbocyclic rings are found in bacteria and plants. Bacteria synthesize cyclopropane fatty acids (CPA-FAs) only by the addition of a methylene group from S-adenosylmethionine to the cis-double bond of monoenoic phospholipid-bound fatty acids. In plants CPA-FAs are usually minor components with cyclopropene fatty acids (CPE-FAs) more abundant. Sterculia, foetida seed oil contains 65-78% CPE-FAs, principally sterculic acid. To address carbocyclic fatty acid synthesis in plants, a cDNA library was constructed from developing seeds during the period of maximum oil deposition. About 0.4% of 5,300 expressed sequence tags were derived from one gene, which shared similarities to the bacterial CPA-FA synthase. However, the predicted protein is twice as large as the bacterial homolog and represents a fusion of an FAD-containing oxidase at the N terminus and a methyltransferase at the C terminus. Functional analysis of the isolated full-length cDNA was conducted in tobacco suspension cells where its expression resulted in the accumulation of up to 6.2% dihydrosterculate of total fatty acids. In addition, the dihydrosterculate was specifically labeled by [methyl-C-14]methionine and by [C-14]oleic acid in the transgenic tobacco cells. In in vitro assay of S. foetida seed extracts, 5-adenosylmethionine served as a methylene donor for the synthesis of dihydrosterculate from oleate. Dihydrosterculate accumulated largely in phosphatidylcholine in both systems. Together, a CPA-FA synthase was identified from S. foetida, and the pathway in higher plants that produce carbocyclic fatty acids was defined as by transfer of C, units, most likely from S-adenosylmethionine to oleate.