In human milk fat, palmitic acid (16:0) is esterified to the middle (sn-2 or β) position on the glycerol backbone and oleic acid (18:1) predominantly to the outer positions, giving the triacylglycerol (TG) a distinctive stereoisomeric structure that is believed to assist nutrient absorption in the infant gut. However, the fat used in most infant formulas is derived from plants, which preferentially esterify 16:0 to the outer positions. We have previously showed that the metabolism of the model oilseed Arabidopsis thaliana can be engineered to incorporate 16:0 into the middle position of TG. However, the fatty acyl composition of Arabidopsis seed TG does not mimic human milk, which is rich in both 16:0 and 18:1 and is defined by the high abundance of the TG molecular species 1,3-olein-2-palmitin (OPO). Here we have constructed an Arabidopsis fatty acid biosynthesis 1-1 fatty acid desaturase 2 fatty acid elongase 1 mutant with around 20% 16:0 and 70% 18:1 in its seeds and we have engineered it to esterify more than 80% of the 16:0 to the middle position of TG, using heterologous expression of the human lysophosphatidic acid acyltransferase isoform AGPAT1, combined with suppression of LYSOPHOSPHATIDIC ACID ACYLTRANSFERASE 2 and PHOSPHATIDYLCHOLINE:DIACYLGLYCEROL CHOLINEPHOSPHOTRANSFERASE. Our data suggest that oilseeds can be engineered to produce TG that is rich in OPO, which is an important structured fat ingredient used in infant formulas.

中文翻译：

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在拟南芥种子中生产婴儿配方奶粉成分1,3-油精-2-棕榈酸

在人乳脂肪中，棕榈酸（16：0）被酯化到甘油骨架的中间位置（sn-2或β），而油酸（18：1）主要被酯化到外部位置，从而使三酰甘油（TG）独特的立体异构结构被认为有助于婴儿肠道中营养的吸收。但是，大多数婴儿配方食品中使用的脂肪均来自植物，这些植物优先将16：0酯化至外部位置。先前我们已经证明了模型油料种子拟南芥的代谢可以设计成将16：0纳入TG的中间位置。但是，拟南芥种子TG的脂肪酰基组成不能模仿人乳，后者富含16：0和18：1，并且由TG分子种类1,3-油精-2-棕榈酸（ OPO）。在这里我们构建了拟南芥脂肪酸的生物合成1-1脂肪酸去饱和酶2脂肪酸延伸酶1突变体，其种子中约有20％16：0和70％18：1，我们利用人溶血磷脂酸酰基转移酶同工型的异源表达，对其进行了工程改造，使其酯化了TG中80％以上的16：0 AGPAT1，与溶血磷脂酸酰基转移酶2和磷脂酰胆碱：二环甘油胆碱磷酸转移酶的抑制相结合。我们的数据表明，油籽可以被工程化生产富含OPO的TG，这是婴儿配方食品中使用的重要结构化脂肪成分。