第310期 文献解读-蓝藻也能生产油?-三酰甘油和植酸酯在Synechocystis sp. PCC6803中的合成

杂志-PNAS

影响因子：9.504

发表时间：2020.02.03

摘要

蓝藻是一种单细胞原核藻类，与植物相似，可进行含氧光合作用。该细胞含有类囊体膜，由与植物叶绿体相关的脂类组成，以适应光合作用的复合体。在植物、动物和一些细菌中发现的储存脂质，包括三酰甘油或蜡酯，但在蓝藻中仍未探究清楚。我们在这里展示了蓝藻Synechocystis sp. PCC68033可同时累积集三酰甘油和蜡酯(脂肪酸植酸酯)的可能性。植物酯在非生物胁迫条件下积累水平较高。分析表明，与植物酯酶/脂肪酶/硫酯酶(ELT)蛋白序列相似的酰基转移酶slr 2103是蓝藻合成三酰甘油和植酸酯所必需的。重组酶slr 2103对植酸和二酰基甘油具有酰基转移酶活性，从而产生植酸酯和三酰甘油。Acyl-CoA硫酯是首选的酰基供体，而acyl-ACP (酰基载体蛋白)、游离脂肪酸或半乳糖脂结合脂肪酸则是较差的底物。Slr 2103蛋白序列与细菌(ATFA)或植物的酰基转移酶(DGAT1，DGAT2，PDAT)无关，因此建立了一组独立的细菌酰基转移酶，参与三酰甘油和蜡酯的合成通路。蓝藻中三酰甘油的合成基因Slr 2103的鉴定为原核光合细胞在生物技术中的应用开辟了可能性。

 Fig. 1.Phylogenetic relationship of lipid acyltransferases from cyanobacteria, plants, and green and red algae. Protein sequences were aligned with ClustalW, and a phylogenetic tree constructed using the Neighbor Joining method with 1,000 bootstrap repetitions (Mega 10.0.5). For plant ELT sequences, only the C-terminal acyltransferase-like parts were considered. A. baylyi (ADP1) Ab-WS/DGAT, AF529086.1; Anabaena sp. (CA = ATCC 33047) WP_066380359; Arabidopsis thaliana At-PES1 (amino acids 401–704), At-PES2 (401-701), At-DGAT1, At-WSD1; Calothrix brevissima WP_096644248; C. reinhardtii Cre01g017100 (591-911), Cre08g365950 (411-692), Cre12g521650 (631-873); Chondrus crispus XP_005713590 (601-965); Cyanothece sp. (PCC 7425) WP_012629067; Galdieria sulphuraria XP_005702844 (561-921); Synechococcus sp. (NKBG042902) WP_030007836; and Synechocystis sp. (PCC 6803) slr2103, sll1848, slr2060, sll1752.

Fig. 4.The number of lipid droplets in Synechocystis Δslr2103 is decreased. Synechocystis WT and Δslr2103 mutant were grown in BG-11 medium and the cells observed by transmission electron microscopy.

原文标题、作者、摘要

Triacylglycerol and phytyl ester synthesis in Synechocystis sp. PCC6803

Mohammed Aizouqa, Helga Peiskera, Katharina Gutbroda, Michael Melzerb, Georg Hölzla, and Peter Dörmanna,1

Abstract

Cyanobacteria are unicellular prokaryotic algae that perform oxygenic photosynthesis, similar to plants. The cells harbor thylakoid membranes composed of lipids related to those of chloroplasts in plants to accommodate the complexes of photosynthesis. The occurrence of storage lipids, including triacylglycerol or wax esters, which are found in plants, animals, and some bacteria, nevertheless remained unclear in cyanobacteria. We show here that the cyanobacterium Synechocystis sp. PCC6803 accumulates both triacylglycerol and wax esters (fatty acid phytyl esters). Phytyl esters accumulate in higher levels under abiotic stress conditions. The analysis of an insertional mutant revealed that the acyltransferase slr2103, with sequence similarity to plant esterase/lipase/thioesterase (ELT) proteins, is essential for triacylglycerol and phytyl ester synthesis in Synechocystis. The recombinant slr2103 enzyme showed acyltransferase activity with phytol and diacylglycerol, thus producing phytyl esters and triacylglycerol. Acyl-CoA thioesters were the preferred acyl donors, while acyl-ACP (acyl carrier protein), free fatty acids, or galactolipid-bound fatty acids were poor substrates. The slr2103 protein sequence is unrelated to acyltransferases from bacteria (AtfA) or plants (DGAT1, DGAT2, PDAT), and therefore establishes an independent group of bacterial acyltransferases involved in triacylglycerol and wax ester synthesis. The identification of the gene slr2103 responsible for triacylglycerol synthesis in cyanobacteria opens the possibility of using prokaryotic photosynthetic cells in biotechnological applications.

Keywords: cyanobacteria triacylglycerol wax acyltransferase

解读人：曾铁鑫