Structural and Mechanistic Investigations of Antibiotic Production in Bacteria

抗生素耐药性是一个无可争议的问题，迫切需要发现和开发生产成本有效的新抗生素。2017年2月，世界卫生组织（WHO）发布了首份对人类健康构成严重风险的抗生素耐药优先病原体清单。这份清单包括高度优先的目标，如广为宣传的耐甲氧西林金黄色葡萄球菌（MRSA），并明确认识到需要采取紧急行动和研究新的抗生素。然而，在这个令人担忧的标题下，对新抗生素研发的投资下降导致了新药物发现数量的急剧下降，以及能够提供这些药物的知识和专业知识的减少。天然产品及其衍生物已经并将继续是这些对人类和动物健康至关重要的抗生素的重要来源。聚酮化合物是一类天然产物，包括抗生素等高价值化合物。它们来源广泛，包括细菌和真菌。在过去的50年里，人们对自然界中抗生素合成的非常复杂和多样的方式有了一些了解。虽然细菌和真菌可能被视为简单的有机体，但它们在优雅和效率方面可以说胜过世界上最好的合成化学家，而我们希望利用的正是这种力量。通过充分了解自然界的生物合成机制，我们可以设计出新的生物活性化合物的途径，事实证明，许多抗生素是由微生物内部的巨型蛋白质组装体催化的一系列化学反应产生的，这些巨型蛋白质组装体就像是纳米级的工厂。简单的有机分子在一端被激活和加载，连接在一起，然后在另一端作为完成的（通常是精心制作的）产品释放出来。这些纳米工厂将简单的积木连接到单个模块的装配线上，类似于一组机器人在汽车制造中执行操作。因此，每种抗生素的化学结构是由存在于装配线每个阶段的酶决定的，蓝图是生物合成基因簇。我们了解建造这些工厂的一些规则，可以重新排列模块的顺序来生产新的化合物，但有时这只是打破了装配线，或者生产出意想不到的化合物。这表明我们并不真正了解它们是如何进化到一起的，我们也不知道所需的所有化学步骤。我们的目的是调查两个不同的“工厂”，生产抗MRSA抗生素。第一个生产莫匹罗星，这是商业上使用，但仅限于局部使用和鼻喷雾剂，因为它的不稳定性。第二种是thiomarinol，结构上与莫匹罗星相关，但具有可能导致更广泛应用的特征。在这两个系统中，大量重要的生物合成步骤还没有完全理解。结合化学家，生物化学家，结构生物学家和分子建模师的专业知识，我们将阐明这些步骤，这可能导致更稳定的莫匹罗星版本。我们还将使用这些系统来回答相当普遍的问题，这样我们就可以以合理的方式建立新的化合物的新途径。

There is an indisputable problem of antibiotic resistance and an urgent need for the discovery and development of new antibiotics that are cost effective to produce. In February 2017, the World Health Organisation (WHO) published its first ever list of antibiotic resistant priority pathogens that pose serious risks to human health. This list includes high priority targets such as the well-publicised methicillin resistant Staphylococcus aureus (MRSA) and there is clear recognition that urgent action and research into new antibiotics is required. However against this alarming headline, a drop in investment in research and development into new antibiotics has led to a dramatic fall in the number of new drugs being discovered and a reduction in knowledge and expertise that is capable of delivering them.Natural products and their derivatives have, and will continue to be, an important source of these antibiotics that are critical for human and animal health. Polyketides are a family of natural products which include high value compounds including antibiotics. They are derived from a wide range of sources including bacteria and fungi. Over the last fifty years some understanding of the remarkably complex and diverse ways in which antibiotics are synthesised in Nature has been gained. Whilst bacteria and fungi might be viewed as simple organisms, they arguably outperform the world's best synthetic chemists in terms of their elegance and efficiency and it is this power we wish to harness. By fully understanding nature's biosynthetic machinery we can engineer pathways to deliver new bioactive compounds.It turns out that many antibiotics are made by a series of chemical reactions catalysed by megaprotein assemblies that act as nano-scale factories inside the microbe. Simple organic molecules are activated and loaded at one end, joined together and then released as completed (usually elaborate) products at the other end. The nano-factories join the simple building blocks on an assembly line of individual modules, akin to a group of robots performing operations in vehicle manufacture. The chemical structure of each antibiotic is thus determined by the enzymes present at each stage of the assembly line, the blueprint being the biosynthetic gene cluster. We understand some rules for building these factories and can rearrange the order of modules to produce new compounds, but sometimes this just breaks the assembly line, or produces an unexpected compound. This reveals we don't truly understand how they have evolved to fit together and we do not know all of the chemical steps required. Our aim is to investigate two different "factories" that produce anti-MRSA antibiotics. The first produces mupirocin, which is used commercially but is restricted to topical use and in nasal sprays because of its instability. The second is thiomarinol, structurally related to mupirocin, but has features that might lead to wider applications. A substantial number of important biosynthetic steps are not fully understood in both of these systems. Combining the expertise of chemists, biochemists, structural biologists and molecular modellers we will elucidate these steps which could lead to a more stable version of mupirocin. We will also use these systems to answer quite general questions so we can build new pathways to novel compounds in a rational way.