Interrogating the nisin:lipid II interaction: a chemical biology approach

抗生素耐药性细菌感染正在成为全球公共卫生的日益严重的威胁。最近出版的一份英国政府文件，奥尼尔报告（2016）估计，如果我们不解决这个问题，到2050年，每年可能会有1000万人丧生。问题的部分原因是，几十年来，工业界对新抗菌剂的投资很少，最后一类新抗生素是在30多年前发现的。这引起了人们对天然产物作为强效抗菌药物来源的新兴趣。作为可能的先导物而被深入研究的一类天然产物是羊毛硫抗生素。其中最著名的是乳酸链球菌素，它是由一种细菌菌株产生的，目的是杀死竞争细菌，多年来一直被成功地用作食品防腐剂。然而，其复杂的结构，合成困难和不良的生物学特性意味着它尚未被开发作为一种可能的抗微生物药物来对抗人类的细菌感染。已知乳链菌肽靶向复合脂质，脂质II，其仅在细菌中发现。由于脂质II对于细菌能够合成其细胞壁至关重要，因此细菌难以对靶向脂质II的抗微生物剂产生抗性。重要的是，乳链菌肽和脂质II结合在一起形成有序的孔结构，导致细菌膜破裂和细菌细胞死亡。因此，我们必须了解这种孔是如何形成的，以及乳链菌肽和脂质II组分之间的重要相互作用是什么：然而，目前用于研究膜中孔结构的技术没有足够高的分辨率来观察这些相互作用的细节。合作的研究小组先前已经开发出合成乳链菌肽和脂质II的具有挑战性的结构的强大方法，用于分析脂质膜中的孔如何形成，以及用于筛选针对病原体（如MRSA）的新抗菌剂。在这个提议中，我们将系统地设计和合成尼生素和脂质II的变体，然后针对每个结构变体，我们将尝试组装孔复合物。这一过程类似于在纳米尺度上拼凑一个三维拼图，一个接一个地改变拼图的每一个部分，看看乳链菌肽和脂质II的哪些部分对成功组装至关重要，哪些部分不参与复合物的形成。这些信息将导致乳酸链球菌素：脂质II孔结构的详细模型，并最终使制药公司能够设计简化的羊毛硫抗生素作为下一代抗菌剂的领导者。

Antibiotic resistant bacterial infections are becoming an increasing threat to global public health. A recently published UK Government document, the O'Neill report (2016) estimates that 10 million lives a year could be lost by 2050 if we do not tackle this issue. Part of the problem is that little investment in new antimicrobials has taken place in industry in decades, with the last new class of antibiotics discovered over 30 years ago. This has generated a renewed interest in natural products as a source of potent antimicrobial drugs. One class of natural products that are being intensively studied as possible leads are the lantibiotics. The best known of these, nisin, is produced by one strain of bacteria in order to kill off competing bacteria, and has been successfully used as a food preservative for many years. However, its complex structure, difficulties in synthesis, and poor biological properties mean that is has not yet been exploited as a possible antimicrobial drug to combat bacterial infections in humans. It is known that nisin targets a complex lipid, lipid II, which is only found in bacteria. As lipid II is critical for bacteria to be able to synthesise their cell wall, it is difficult for bacteria to evolve resistance to antimicrobial agents that target lipid II. Importantly, nisin and lipid II fit together to form an ordered pore structure that results in rupture of the bacterial membrane and the death of the bacterial cell. It is therefore very important that we understand how this pore forms and what the important interactions are between the nisin and lipid II components: however, current techniques for studying the structure of pores in membranes do not have high enough resolution to see the details of these interactions.The collaborating research groups have previously developed powerful methods for synthesising the challenging structures of nisin and lipid II, for analyzing how pore form in lipid membranes, and for screening new antibacterials against pathogens such as MRSA. In this proposal, we will systematically design and synthesise variants of nisin and lipid II, and for each structural variation we will then try to assemble the pore complex. The process will be akin to piecing together a 3-D jigsaw at the nanoscale, varying each of the pieces of the jigsaw one by one, to see which parts of the nisin and lipid II are crucial to successful assembly, and which parts are not involved in complex formation. This information will lead to a detailed model for the nisin:lipid II pore structure, and will eventually enable pharmaceutical companies to design simplified lantibiotics as leads for next generation antimicrobials.