Chemoenzymatic synthesis of macrolactones utilizing PolyketideSynthases (PKSs) for the generation of novel macrolide antibiotics

提案摘要 介导构建大量天然产物的大合成酶代表了一些最重要的 复杂的分子机器。在谢尔曼组中，聚酮脱氢酶（PKS）是来自 多学科视角。PKS负责多种次生代谢产物的生物合成， 经济和治疗重要性，包括抗生素、抗癌剂和免疫调节剂。抗生素 根据世界卫生组织（WHO），耐药性是全球健康的最大威胁之一。的 疾病控制和预防中心（CDC）显示，仅在美国，它就导致超过200万人死亡。 感染和23,000人死亡。据估计，这些令人震惊的数字将在每一年继续增加。 2050年，全球估计有1000万人死亡。由于这些原因，我们有动机利用PKS 促进大环内酯类新型抗生素的设计和产生， 新的有效的治疗方法。 PKS的不同子集产生对于大环内酯生产必不可少的大环系统，包括 Pikromycin（Pik）、Erythromycin（DEBS）和Tylosin（Tyl）生产微生物的途径。在这 在这个项目中，我将专注于使用合成方法来促进这些化合物的组装， 它们的类似物使用生物催化和酶工程。不同聚酮扩链剂的合成 中间体与后期生物合成机制（如糖基转移酶，P450 单加氧酶）促进有效地获得新分子的库，这对 单独使用合成方法产生。PKS酶提供了一种选择性催化关键酶的强有力的方法， 通过在聚酮链上进行转化以产生大环内酯，其随后可以转化为新的聚酮化合物。 大环内酯类抗生素。 谢尔曼实验室以前的工作表明，将PKS模块应用于 不同大环内酯的生产取决于Pik硫酯酶（TE）结构域的选择性。这些发现 提出TE在处理非天然底物以产生新的 大环化合物在本研究中，我计划（1）设计合成非天然底物来探索PKS 对底物负载、延伸和环化的选择性和耐受性，以产生奇数- （2）追求TE定向进化方法以提高总周转率，以及 扩大底物范围，生成新的大环内酯类产品;（3）将化学酶法合成应用于 不同的大环内酯类化合物，并确定它们对人类细菌病原体的生物活性谱。这些努力将 对开发新的大环内酯类抗生素以控制和克服人类新出现的耐药性至关重要 细菌病原体，并改善这类重要的抗感染剂的治疗参数。

Proposal Summary The megasynthases that mediate construction of a vast array of natural products represent some of the most complex molecular machines in Nature. In the Sherman group, polyketide synthases (PKSs) are of interest from a multi-disciplinary perspective. PKSs are responsible for the biosynthesis of diverse secondary metabolites of economic and therapeutic importance including antibiotics, anticancer agents and immune-modulators. Antibiotic resistance is one of the biggest threats of global health according to the World Health Organization (WHO). The Centers for Disease Control and Prevention (CDC) showed that in the US alone, it causes more than 2 million infections and 23,000 deaths a year. These alarming numbers are estimated to continue incrementally every year, with 10 million estimated deaths worldwide in 2050. For these reasons, we are motivated to utilize PKSs to facilitate the design and generation of novel antibiotics from the macrolides class to improve the development of new, effective therapeutics. A diverse subset of PKSs generate macrocyclic ring systems that are essential for macrolide production, include pathways from the Pikromycin (Pik), Erythromycin (DEBS) and Tylosin (Tyl) producing microorganisms. In this project, I will be focusing on the use of synthetic approaches to facilitate assembly of these compounds and their analogs using biocatalysis and enzyme engineering. The synthesis of diverse polyketide chain elongation intermediates in conjunction with late-stage biosynthetic machinery (e.g. glycosyltransferases, P450 monooxygenases) facilitates efficient access to a repertoire of novel molecules, which are challenging to generate using synthetic methods alone. PKS enzymes provide a powerful method to selectively catalyze key transformations on polyketide chains to generate macrolactones, which can be subsequently converted to novel macrolide antibiotics. Previous work in the Sherman lab has revealed that the primary hurdle to applying PKS modules for the production of diverse macrolactones hinges on the selectivity of the Pik thioesterase (TE) domain. These findings suggested that the TE functions as a gatekeeper in the processing of unnatural substrates to generate novel macrocycles. In the proposed research, I plan to (1) Design and synthesize unnatural substrates to explore PKS selectivity and tolerance toward substrate loading, elongation, and cyclization for the generation of odd- membered ring macrolactones, (2) Pursue a TE directed evolution approach for improved total turnover, and expansion of substrate scope to generate new macrolactone products, (3) Apply chemoenzymatic synthesis for diverse macrolides and determine their bioactivity profile against human bacterial pathogens. These efforts will be crucial to developing new macrolide antibiotics to control and overcome emerging resistance in human bacterial pathogens and to improve therapeutic parameters in this important class of anti-infective agents.