Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, University of Goettingen, 37077, Goettingen, Germany.
Department of Plant Biochemistry, Goettingen Center for Molecular Biosciences (GZMB), University of Goettingen, 37077, Goettingen, Germany.
BMC Plant Biol. 2018 Nov 26;18(1):298. doi: 10.1186/s12870-018-1510-3.
Oleaginous microalgae are promising sources of energy-rich triacylglycerols (TAGs) for direct use for food, feed and industrial applications. Lobosphaera incisa is a fresh water unicellular alga, which in response to nutrient stress accumulates a high amount of TAGs with a high proportion of arachidonic acid (ARA). The final committed step of de novo TAG biosynthesis is catalyzed by acyl-CoA:diacylglycerol acyltransferases (DGATs), which add a fatty acid (FA) to the final sn-3 position of diacylglycerol (DAG).
Genome analysis revealed the presence of five putative DGAT isoforms in L. incisa, including one DGAT of type 1, three DGATs of type 2 and a single isoform of a type 3 DGAT. For LiDGAT1, LiDGAT2.1, LiDGAT2.2 and LiDGAT2.3 enzyme activity was confirmed by expressing them in the TAG-deficient yeast strain H1246. Feeding experiments of yeast transformants with fatty acids suggest a broad substrate specificity spectrum for LiDGAT1. A significant TAG production in response to exogenous ARA was found for LiDGAT2.2. Cellular localization of the four type 1 and type 2 DGATs expressed in yeast revealed that they all localize to distinct ER domains. A prominent association of LiDGAT1 with ER domains in close proximity to forming lipid droplets (LDs) was also observed.
The data revealed a distinct molecular, functional and cellular nature of type 1 and type 2 DGATs from L. incisa, with LiDGAT1 being a major contributor to the TAG pool. LiDGATs of type 2 might be in turn involved in the incorporation of unusual fatty acids into TAG and thus regulate the composition of TAG. This report provides a valuable resource for the further research of microalgae DGATs oriented towards production of fresh-water strains with higher oil content of valuable composition, not only for oil industry but also for human and animal nutrition.
产油微藻是一种很有前途的能源来源，可用于直接生产富含三酰基甘油(TAG)的食物、饲料和工业应用。新月菱形藻是一种淡水单细胞藻类，在营养胁迫下会积累大量的三酰基甘油(TAG)，其中花生四烯酸(ARA)的比例很高。从头生物合成 TAG 的最终关键步骤是由酰基辅酶 A：二酰基甘油酰基转移酶(DGAT)催化的，该酶将脂肪酸(FA)添加到二酰基甘油(DAG)的最终 sn-3 位置。
基因组分析显示，新月菱形藻中存在 5 种假定的 DGAT 同工型，包括 1 种 1 型 DGAT、3 种 2 型 DGAT 和 1 种 3 型 DGAT。通过在 TAG 缺陷型酵母菌株 H1246 中表达 LiDGAT1、LiDGAT2.1、LiDGAT2.2 和 LiDGAT2.3，证实了它们的酶活性。用脂肪酸对酵母转化体进行喂养实验表明，LiDGAT1 具有广泛的底物特异性谱。发现 LiDGAT2.2 对外源 ARA 有显著的 TAG 生成反应。在酵母中表达的 4 种 1 型和 2 型 DGAT 的细胞定位表明，它们都定位于不同的内质网(ER)域。还观察到 LiDGAT1 与形成脂滴(LD)的 ER 域密切相关。
数据揭示了新月菱形藻 1 型和 2 型 DGAT 的独特的分子、功能和细胞特性，LiDGAT1 是 TAG 库的主要贡献者。2 型的 LiDGAT 可能反过来参与将不寻常的脂肪酸掺入 TAG 中，从而调节 TAG 的组成。本报告为进一步研究微藻 DGAT 提供了有价值的资源，旨在生产具有更高油含量和更有价值成分的淡水藻株，不仅对石油工业，而且对人类和动物营养也有重要意义。
