Enzymes of plant gallotannin metabolism

没食子丹宁的积累已被证明是一系列双子叶植物和简单绿藻的普遍化学性状。没食子丹宁是一种有效的蛋白质络合多酚，是抵御微生物病原体和食草动物的化学防御的一部分。没食子单宁的生物合成依赖于没食子酸的形成和一系列酰基转移反应，以产生1,2,3,4,6-五- o -没食子单宁葡萄糖。在这个项目中，我们将使用基于同源性的克隆方法分离编码该代谢途径必需酶的cdna -脱氢shikimate脱氢酶，UDP葡萄糖：没食子酸葡萄糖基转移酶和一组位置特异性没食子酸转移酶，这些酶使用ß-缩醛酯1- o -没食子酸葡萄糖作为酰基供体。没食子酰基转移酶形成了一类新的植物酰基转移酶，与ß-葡萄糖苷酶样水解酶相关。通过定点诱变和反应机理的动力学表征，将阐明没食子酰基转移酶活性的分子决定因素。鉴定的序列将被用于将复杂的没食子丹素代谢途径转移到模式生物中，其长期目标是提高植物对病原体的抵抗力，并实现为工业应用量身定制没食子丹素的生产。

The accumulation of gallotannins has been documented as a prevalent chemical trait in a range of dicotyledonous plants and simple green algae. Gallotannins, potent protein-complexing polyphenols, form part of the chemical defense against microbial pathogens and herbivores. The biosynthesis of gallotannins depends on the formation of gallic acid and a series of acyltransfer reactions to yield 1,2,3,4,6-penta-O-galloylglucose. In this project we will use homology-based cloning approaches to isolate cDNAs encoding the essential enzymes of this metabolic pathway - dehydroshikimate dehydrogenase, UDP glucose:gallic acid glucosyltransferase and a group of position-specific galloyl transferases, which employ the ß-acetal ester 1-O-galloylglucose as acyl donor. The galloyltransferases form a novel group of plant acyltransferases related to ß-glucosidase-like hydrolases. By site-directed mutagenesis and kinetic characterization of the reaction mechanism the molecular determinants of galloyltransferase activity will be elucidated. The identified sequences will be exploited to transfer the complex gallotannin metabolic pathway to model organisms with the longterm goals to increase plant pathogen resistance and to implement the production of tailored gallotannins for industrial application.