Glycoengineering of cyanobacterial thylakoid membranes for future studies on the role of glycolipids in photosynthesis
Glycoengineering of cyanobacterial thylakoid membranes for future studies on the role of glycolipids in photosynthesis
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DOI：
10.1093/pcp/pci189
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发表时间：
2005-11-01
影响因子：
4.9
通讯作者：
Heinz, E
中科院分区：
文献类型：
--
作者：
Hölzl, G;Zähringer, U;Heinz, E
从蓝藻到被子植物类囊体膜的脂质组成是保守的。主要成分是单半乳糖基和双半乳糖基二酰基甘油。在蓝细菌中，类囊体膜生物合成开始于单葡萄糖基二酰基甘油的形成，该单葡萄糖基二酰基甘油被C4-差向异构化为相应的半乳糖脂，而在质体中，单半乳糖基二酰基甘油在开始时形成。这表明半乳糖脂在类囊体中具有特定的功能。我们想研究半乳糖脂是否可以被糖基二酰基甘油取代，糖基二酰基甘油的头基在其差向异构体和异头异构体的细节以及在二糖基二酰基甘油的末端己糖的连接点上不同。为此目的，在数据库中鉴定推定的糖基转移酶序列以用于在各种宿主生物体中的功能表达。从18个新发现的序列中，有4个编码糖基转移酶，催化糖脂生物合成的最后步骤：两个α-葡糖基转移酶，一个β-半乳糖基转移酶和一个β-葡糖基转移酶。他们的功能注释是基于详细的结构表征的新糖脂中形成的cysterosols以及在体外酶测定。α-葡糖基转移酶在蓝细菌聚球藻中的表达导致了新的α-半乳糖基二酰基甘油的积累，这归因于相应的糖脂的差向异构化。β-葡糖基转移酶的表达导致高比例的新β-葡糖基-（1 -> 6）-β-半乳糖基二酰基甘油几乎完全取代天然二半乳糖基二酰基甘油。这些结果表明，类囊体中糖脂模式的修饰是可能的。
The lipid composition of thylakoid membranes is conserved from cyanobacteria to angiosperms. The predominating components are monogalactosyl- and digalactosyldiacylglycerol. In cyanobacteria, thylakoid membrane biosynthesis starts with the formation of monoglucosyldiacylglycerol which is C4-epimerized to the corresponding galactolipid, whereas in plastids monogalactosyldiacylglycerol is formed at the beginning. This suggests that galactolipids have specific functions in thylakoids. We wanted to investigate whether galactolipids can be replaced by glycosyldiacylglycerols with headgroups differing in their epimeric and anomeric details as well as the attachment point of the terminal hexose in diglycosyldiacylglycerols. For this purpose putative glycosyltransferase sequences were identified in databases to be used for functional expression in various host organisms. From 18 newly identified sequences, four turned out to encode glycosyltransferases catalyzing final steps in glycolipid biosynthesis: two alpha-glucosyltransferases, one beta-galactosyltransferase and one beta-glucosyltransferase. Their functional annotation was based on detailed structural characterization of the new glycolipids formed in the transformant hosts as well as on in vitro enzymatic assays. The expression of alpha-glucosyltransferases in the cyanobacterium Synechococcus resulted in the accumulation of the new alpha-galactosyldiacylglycerol which is ascribed to epimerization of the corresponding glucolipid. The expression of the beta-glucosyltransferase led to a high proportion of new beta-glucosyl-(1 -> 6)-beta-galactosyldiacylglycerol almost entirely replacing the native digalactosyldiacylglycerol. These results demonstrate that modifications of the glycolipid pattern in thylakoids are possible.