杀稻瘟菌素类肽核苷关键生物合成步骤和新颖抗性机制的酶学研究

杀稻瘟菌素S(BS)是由链霉菌产生的4'-氨酰基-4'-脱氧己糖胞嘧啶，由于其良好的生物活性和对鱼类无害，成为第一例大规模用于防治水稻稻瘟病的汞取代抗生素。BS和它的抗性基因现在被广泛应用于真核细胞转基因的筛选。BS结构中蕴含了一个独特的酶学反应：己糖C2-C3位两次脱水形成烯键；BS生物合成过程中还包含了一个新颖的抗性机制：BS亮氨酸酰化及其成熟；此外，4'-氨酰基-4'-脱氧己糖胞嘧啶生物合成中的共性问题：胞嘧啶葡萄糖醛酸C4位羟基成酮再转氨过程，都没有实验数据支持。本项目在综合比较分析杀稻瘟菌素，米多霉素，精霉素和古氏菌素四个结构类似物生物合成的研究成果基础上，重新推导了杀稻瘟菌素的生物合成途径，拟通过体外反应和体内敲除来阐明以上科学问题，为提升对这一类抗生素生物合成的了解提供实验证据。

Blasticidin S, a 4'-aminoacyl-4'-deoxyhexose cytosine produced by Streptomyces griseochromogenes, was the first antibiotic used in large scale in replace of mercurial to fight against rice blast due to its good fungicidal activity as well as the harmlessness to fishes. Blasticidin S and its resistance gene bsd have been increasingly used as the selection marker in the transgenic studies.BS features a unique C2=C3 double bond of the pyranoside ring that implies two dehydrations; the leucyl acylation of the beta-amino group of arginine, but finally hydrolysed during the maturation of BS was reported as a novel self-resistance;In addition, the common biosynthetic steps for the 4'-aminoacyl-4'-adeoxyhexose, such as the oxidation of 4-hydroxyl group of the cytosylglucuronic acid(CGA) into 4-keto-CGA and fowllowed by amination of the keto group into 4-amino-CGA, were also proposed but in need of experimental proof to support. Based on the overall comparative analysis of the previous biosysnthetic studies on the blasticidin S,mildomycin,arginomycin and gougerotin, we revised and proposed a complete pathway for BS biosynthesis. This project will study above mentioned questions in vivo and in vitro,and aims to provide the insights into the biosynthesis of this type of nucleoside.