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

耐抗生素细菌感染正日益成为对全球公共卫生的威胁。最近发布的英国政府文件奥尼尔报告（2016年）估计，如果我们不解决这一问题，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，工业对新型抗菌剂的投资很少，最后一类新型抗生素是在30多年前发现的。这重新引起了人们对天然产物作为强效抗菌药物来源的兴趣。作为可能的先导物，正在被深入研究的一类天然产物是抗生素。其中最著名的是乳酸链球菌素，它是由一种细菌产生的，目的是杀死竞争的细菌，多年来一直被成功地用作食品防腐剂。然而，其复杂的结构、合成困难和较差的生物学特性意味着它还没有被开发成一种可能的抗细菌药物来对抗人类的细菌感染。众所周知，nisin针对的是一种复杂的脂质，脂质II，这种脂质只存在于细菌中。由于脂质II对于细菌能够合成其细胞壁至关重要，因此细菌很难进化出对靶向脂质II的抗菌剂的耐药性。重要的是，nisin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，我们了解这种孔是如何形成的以及nisin和脂质II组分之间的重要相互作用是非常重要的：然而，目前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。合作研究小组之前已经开发了强大的方法来合成nisin和脂质II的具有挑战性的结构，用于分析脂质膜中的孔是如何形成的，以及用于筛选针对MRSA等病原体的新抗生素。在本提案中，我们将系统地设计和合成nisin和脂质II的变体，并且对于每种结构变体，我们将尝试组装孔隙复合物。这个过程将类似于在纳米尺度上拼凑一个3d拼图，一个接一个地改变拼图的每一块，看看nisin和脂质II的哪些部分对成功组装至关重要，哪些部分不参与复杂的形成。这些信息将导致nisin：脂质II孔隙结构的详细模型，并最终使制药公司能够设计简化的l抗生素作为下一代抗菌素的先导。

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.