Biosynthesis of polyketide antibiotic mupirocin by Pseudomonas fluorescens

生物系统为许多不同的目的构建复杂的分子——细胞和超细胞结构的构建模块，驱动活细胞的催化和能量存储系统，允许生物内部和生物之间通信和信息存储的信使分子，以及允许防御或攻击其他生物的分子。人类已经学会了利用这些天然化合物中的许多，尤其是那些作为抗生素的化合物。聚酮化合物是一类非常重要的化合物，因为它们包含许多具有多种结构的分子，这些分子覆盖了一系列有用的活性——不仅仅是抗菌剂，还有抗真菌剂、抗癌剂和抗胆固醇剂，仅举几例。通常，这些化合物的分子“骨架”是通过在装配线上连接简单的构建块来制造的，每个构建块由一个单独的“模块”添加，该模块还将新片段处理为若干（通常是三个）修饰中的一个（称为I型PKS途径）。所得到的分子链可以有不同的长度和修饰组合，然后可以用不同的侧链装饰以产生独特的产品（“剪裁”）。然而，越来越多的非典型途径正在被发现，这些途径似乎使用了尚未定义的额外机制。这些提供了以可控的方式产生新结构的方法。在荧光假单胞菌中发现的一种这样的途径可以合成临床上重要的抗生素莫匹罗星。它对革兰氏阳性细菌最有效，特别是用于对抗MRSA（耐甲氧西林金黄色葡萄球菌），这是最危险的“超级细菌”之一。莫匹罗星的生物合成涉及非典型I型PKS以及大量的“剪裁”酶，其中一些我们已经发现与PKS一起在构建莫匹罗星的骨架中起作用。这与典型的I型PKS模块形成对比，这些模块本身包含构建主干所需的所有信息。该项目整合了微生物分子遗传学、生物化学和化学，研究活细胞和纯化酶的生物合成机制，以了解不同PKS和“定制”成分在构建最终活性产品中的作用。它将探索途径的不同部分所进行的反应及其产生新化合物的灵活性。这些将用于筛选可能用作预防或治疗药物的新生物活性。

Summary Biological systems build complex molecules for many different purposes - building blocks for cells, and supracellular structures, the catalytic and energy storage systems that drive living cells, the messenger molecules that allow communication and information storage within and between organisms and finally the molecules that allow defence or aggression against other organisms. Mankind has learnt to exploit many of these natural compounds, not least those that act as antibiotics. One class of compounds, the polyketides, are of great importance because they include many molecules with a great diversity of structures which cover a whole range of useful activities - not just antibacterials, but also antifungals, anticancer and anticholesterol agents, to name just a few. Typically, the molecular 'backbones' of these compounds are made by joining simple building blocks on an assembly line, each building block being added by a separate 'module' that also processes the new segment to one of a number (normally three) of modifications (known as the Type I PKS pathway). The resulting molecular chain can be of different lengths and combinations of modifications and can then be decorated with different side chains to produce a unique product ('tailoring'). However, an increasing number of atypical pathways are being uncovered that appear to use additional mechanisms not yet defined. These provide ways of producing new structures in a controlled way. One such pathway, found in Pseudomonas fluorescens, synthesises the clinically important antibiotic mupirocin. It is most active against Gram positive bacteria and is particularly used against MRSA (Methicillin Resistant Staphylococcus aureus), one of the most dangerous 'superbugs'. Biosynthesis of mupirocin involves an atypical Type I PKS along with a large number of 'tailoring' enzymes some of which we have discovered act in tandem with the PKS in building the backbone of mupirocin. This is in contrast to typical type I PKS modules which within themselves contain all the information needed to build the backbone. This project integrates microbial molecular genetics, biochemistry and chemistry to study the biosynthetic machinery both in living cells and with purified enzymes to understand the role of the different PKS and 'tailoring' components in building the final active product. It will explore the reactions carried out by different parts of the pathway and their flexibility to produce new compounds. These will be made available for screening for new biological activities that may be of use as prophylactic or therapeutic agents.