基于新型胸腺嘧啶补偿途径的多氧霉素组分多样化的分子机制研究

Polyoxin,a peptidyl nucleoside antibiotic produced by Streptomyces cacaoi var. asoensis and Streptomyces aureochromogenes, respectively,dispalys significant bioactivity against phytopathogenic fungi, as a result, it was used extensively in agricultures since being succesfully created.The struture of polyoxin consists of three building blocks,including nucleoside skeleton,carbamoylpolyoxamic acid and polyoximic acid, and variation of the C-5 modification group R1 in nucleoside skeleton confers the stuctural and bioactive diversity of polyoxin components.Previous studies revealed that the genes responsible for the hydroxylation and caboxylation of C-5 methyl group are unlinked with the polyoxin gene cluster,and implicated that the diversities for the modified groups of C-5 site are associated with a potential novel thymine salvage pathway, thereby indicating the novelty and charm of the molecular mechanisms for component diversification of polyoxin,however,the related molecular mechanism as well as the the novel thymine salvage pathway remained unknown so far.This study aims to elucidate the mechanisms for component diversifiscation of polyoxin and to dissect the novel thymine salvage pathway at molecular level, thereof realizing the component optimization for polyoxin via synthetic biology strategies.

多氧霉素(Polyoxin)属肽核苷类抗生素，由可可链霉菌阿苏变种和金产色链霉菌产生，由于其具有显著的抗植物病原真菌活性，故自创制成功便在农业上广泛使用。多氧霉素的结构由核苷骨架、氨甲酰多氧草氨酸及聚肟酸三个结构单元组成，其中核苷骨架C-5修饰基团R1的变化赋予了多氧霉素组分与活性的多样性。本课题组前期研究揭示，负责核苷骨架C-5甲基羟化与羧化的基因与多氧霉素生物合成基因簇不连锁，并暗示C-5修饰基团的多样性与一个潜在的新型胸腺嘧啶补偿途径相关，由此显示出多氧霉素组分多样化分子机制的新颖性与趣味性，然而迄今为止，相关分子机制与新型胸腺嘧啶补偿途径的功能一直悬而未决。本研究旨在利用生物信息学、遗传学及生物化学手段，从分子水平上阐明多氧霉素组分多样化的机制，并解析新型胸腺嘧啶补偿途径，进而为利用合成生物学策略对多氧霉素进行组分优化。

多氧霉素为肽核苷抗生素，由金产色链霉菌(S. aureochromogenes)和可可链霉菌阿苏变种(S. cacaoi var. asoensis)产生，由于其对农作物、果蔬及一些经济植物真菌病害有良好的防治作用，加之其对环境友好，所以自创制成功以来，便在农业生产上大规模的推广应用。多氧霉素的化学结构由核苷骨架及两个后修饰的氨基酸组成，核苷骨架的C-5修饰不仅影响了多氧霉素的活性和选择性，而且与细菌中一个潜在的胸腺嘧啶补偿途径相关。本项目组综合分子遗传学、生物化学及结构生物学手段，签定了核苷骨架C-5甲基化基因，揭示了甲基化反应的酶学机理，不仅如此，在本项目资助下，成功解析了多氧霉素构造单元氨甲酰多聚草氨酸和核苷骨架重要中间体的生物合成机理。此外，本项目利用途径工程策略对多氧霉素产生菌进行分子改良获得了多氧霉素B和K组分高产菌株，同时利用组合生物学手段产生了多个具有更高生物活性的多氧霉素衍生物，所有这些为多氧霉素产业化技术水平的提升具积极的推动作用。