Comparative genomic analysis revealed a gene for monoglucosyldiacylglycerol synthase, an enzyme for photosynthetic membrane lipid synthesis in cyanobacteria
Comparative genomic analysis revealed a gene for monoglucosyldiacylglycerol synthase, an enzyme for photosynthetic membrane lipid synthesis in cyanobacteria
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DOI：
10.1104/pp.106.082859
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发表时间：
2006-07-01
期刊：
影响因子：
7.4
通讯作者：
Ohta, Hiroyuki
中科院分区：
文献类型：
--
作者：
Awai, Koichiro;Kakimoto, Takatoshi;Ohta, Hiroyuki
蓝细菌具有与植物叶绿体非常相似的类囊体脂质组成，但蓝细菌被提议通过不同的途径合成单半乳糖基二酰基甘油（MGDG），其是光合膜中的主要膜极性脂质。此外，植物MGDG合酶已被克隆，但没有直向同源物已被报道在蓝藻基因组。我们在这里报告的单葡萄糖二酰基甘油（MGlcDG）合酶，催化蓝藻半乳糖脂合成的第一步基因的鉴定。利用比较基因组学分析，基于酶活性在两种蓝藻之间是保守的标准来选择该基因的候选基因（单细胞[集胞藻属PCC 6803]和丝状[鱼腥藻属PCC 7120]），我们假设了该酶的三个特征;也就是说，它具有糖基转移酶基序，福尔斯属于功能未知的基因类别，并且在这两种蓝藻之间具有显著的氨基酸序列相似性。集胞藻的所有基因的基序搜索，BLAST搜索，这两个蓝藻之间的相似性搜索，我们确定了四个候选人的酶，我们预测的所有特征。当在大肠杆菌中表达时，其中一个集胞藻候选蛋白以UDP-葡萄糖依赖的方式显示MGlcDG合酶活性。鱼腥藻中的直系同源物也显示出相同的活性。该酶被预测为需要二价阳离子的活性，这是由生化分析证实。MGlcDG合成酶与植物MGDG合成酶的相似性较低，支持蓝藻和植物利用不同途径合成MGDG的假设。
Cyanobacteria have a thylakoid lipid composition very similar to that of plant chloroplasts, yet cyanobacteria are proposed to synthesize monogalactosyldiacylglycerol (MGDG), a major membrane polar lipid in photosynthetic membranes, by a different pathway. In addition, plant MGDG synthase has been cloned, but no ortholog has been reported in cyanobacterial genomes. We report here identification of the gene for monoglucosyldiacylglycerol (MGlcDG) synthase, which catalyzes the first step of galactolipid synthesis in cyanobacteria. Using comparative genomic analysis, candidates for the gene were selected based on the criteria that the enzyme activity is conserved between two species of cyanobacteria (unicellular [Synechocystis sp. PCC 6803] and filamentous [Anabaena sp. PCC 7120]), and we assumed three characteristics of the enzyme; namely, it harbors a glycosyltransferase motif, falls into a category of genes with unknown function, and shares significant similarity in amino acid sequence between these two cyanobacteria. By a motif search of all genes of Synechocystis, BLAST searches, and similarity searches between these two cyanobacteria, we identified four candidates for the enzyme that have all the characteristics we predicted. When expressed in Escherichia coli, one of the Synechocystis candidate proteins showed MGlcDG synthase activity in a UDP-glucose-dependent manner. The ortholog in Anabaena also showed the same activity. The enzyme was predicted to require a divalent cation for its activity, and this was confirmed by biochemical analysis. The MGlcDG synthase and the plant MGDG synthase shared low similarity, supporting the presumption that cyanobacteria and plants utilize different pathways to synthesize MGDG.