The Mycobacterium tuberculosis Cell Envelope: unravelling complex cell wall assembly, degradation and re-cycling pathways

结核病（TB）是由结核杆菌引起的细菌感染。在世界范围内，结核病仍然是导致死亡和发病的主要细菌原因。2016年，世卫组织报告了1040万新发结核病病例，当年有170万人死于结核病。结核病主要是一种贫困疾病，影响到处于生产年龄的年轻人，因此也带来了巨大的经济负担。生活在低收入和中等收入国家（LMIC）的人口突出了这一情况，这些国家的结核病负担最普遍，发病率和死亡率很高，例如印度（每年510，000人），印度尼西亚（每年130，000人），中国（38，000人），尼日利亚（每年240，000人）南非（97，000人）。因此，向市场推出一种新的结核病药物及其对这些中低收入国家的健康和全球经济的影响是一项紧迫的医疗保健挑战，需要在至少10-15年的时间尺度上加以考虑。我们的申请寻求对结核分枝杆菌细胞包膜研究的支持。所有的细菌细胞都被包围在细胞壁或细胞被膜中。这是一层密集的共价连接的分子围绕细胞膜，保护生物体免受其直接环境的影响。M.结核病非常独特，与其他细菌不同的是，它含有大量独特的脂质（脂肪）和糖。这种高含量的脂质和糖使得M。结核菌的细胞壁对大多数抗生素都是不可渗透的。同时，如果细胞壁有缺陷，生物体非常脆弱。因此，一些现有的TB抗生素干扰细胞壁组分的合成，并且出于同样的原因，许多TB药物开发工作集中在细胞壁上。我们的研究将集中在了解更多关于生物周围的M。结核细胞壁首先，在我们以前对脂质合成的研究的基础上，我们将研究降解脂质的酶系统。这一点很重要，因为M结核病获得营养的机会有限，并已制定了回收分子成分用于新用途的战略。其次，我们将研究M。结核病在其细胞膜外组装糖样聚合物，如阿拉伯半乳聚糖和关键毒力因子脂阿拉伯甘露聚糖。我们的第三个目标是了解一系列酶，这些酶似乎在重塑肽聚糖中发挥作用，肽聚糖是一种常见于细菌中的分子“网格”，但在M.结核第四，我们将使用小规模的机械探针来阐明细菌是如何构建的，并帮助解释关键构件之间的相互作用如何影响毒力。在表征这些生物过程中涉及的酶和蛋白质时，我们的目标是找到作为“好”药物靶点的蛋白质，例如，因为它们是这种生物体所特有的，或者因为当它们被药物灭活时细胞无法补偿。为了实现这一目标，我们的研究将依赖于三个基本的研究支柱：1）基本分枝杆菌蛋白质的鉴定以及如何改善蛋白质靶标和抑制剂之间的相互作用; 2）确定这些化合物如何以及为什么杀死杆菌，它们的作用模式;和3）发展我们与LMICs实验室的合作伙伴关系，例如中国北京药物研究所（IMM）和印度科学研究所（IISc），班加罗尔，印度，并通过我们与葛兰素史克发展中国家疾病（GSK DDW），马德里，西班牙的工业联系，开发药物发现项目，把'命中'变成'铅'，并最终成为新的结核病药物。因此，该提案提供了解决自1882年Robert Koch发现以来一直困扰微生物学家的一系列基本问题的机会，可用于治疗代表21世纪世纪社会最紧迫的医疗保健挑战之一的衰弱性疾病。

Tuberculosis (TB) is a bacterial infection caused by the tubercle bacillus. Worldwide TB remains the leading bacterial cause of mortality and morbidity. In 2016, the WHO reported 10.4 million new cases of TB, with 1.7 million people dying from TB that year. Predominantly a disease of poverty, TB affects young adults in their productive years and hence also carries a large economic burden. This picture is highlighted by populations living in low and middle income countries (LMICs), where the burden of TB is most prevalent, with high morbidity and mortality rates, such as in India (510,000 p.a.), Indonesia (130,000 p.a.), China (38,000 p.a.), Nigeria (240,000 p.a.) and South Africa (97,000 p.a.). Therefore, introducing a new TB drug onto the market and its impact upon the health and global economy for these LMICs represents an urgent healthcare challenge, which needs to be viewed on at least a 10-15-year timescale. Our application seeks support for research into the cell envelope of Mycobacterium tuberculosis. All bacterial cells are enclosed in a cell wall or cell envelope. This is a dense layer of covalently-linked molecules around the cellular membrane, protecting the organism from its immediate environment. The cell wall of M. tuberculosis is very distinctive, differing from other bacteria in containing an exceptional amount of unique lipids (fats) and sugars. This high content of lipids and sugars makes the M. tuberculosis cell wall impermeable to most antibiotics. At the same time, the organism is very vulnerable if the cell wall has defects. Therefore, some existing TB antibiotics interfere with the synthesis of cell wall components, and for the same reason many TB drug development efforts focus on the cell wall. Our research will concentrate on learning more about the biology surrounding the M. tuberculosis cell wall. Firstly, building on our previous studies on lipid synthesis, we will examine enzyme systems that degrade lipids. This is important because M. tuberculosis has limited access to nutrients and has developed strategies to recycle molecular components for new uses. Secondly, we will study how M. tuberculosis assembles sugar-like polymers, such as arabinogalactan and the key virulence factor, lipoarabinomannan, outside of its cell membrane. Our third aim is to understand a range of enzymes that appear to play a role in remodelling peptidoglycan, a molecular 'mesh' that is commonly found in bacteria, but has distinct features in M. tuberculosis. Fourthly, we will use small-scale mechanical probes to clarify how the bacteria are constructed and help explain how interactions of the key building blocks influence virulence. In characterising the enzymes and proteins involved in these biological processes, we aim to find proteins that are 'good' drug targets, for instance because they are unique to this organism or because the cell cannot compensate when they are inactivated by a drug. To achieve this goal, our research will rest on three fundamental research pillars: 1) the identification of essential mycobacterial proteins and how the interaction between the protein target and an inhibitor can be improved; 2) determine how and why these compounds kill bacilli, their mode of action; and 3) develop our partnerships with laboratories in LMICs, such as the Institute of Materia Medica (IMM), Beijing, China and the Indian Institute of Science (IISc), Bangalore, India, and through our industrial links with GlaxoSmithKline Diseases of the Developing World (GSK DDW), Madrid, Spain, develop drug discovery projects to turns 'hits' into 'leads' and ultimately into new TB-drugs. Thus, this proposal offers the opportunity to tackle a range of fundamental questions about an organism that has puzzled microbiologists ever since its discovery by Robert Koch in 1882, that can be used to treat a debilitating disease which represents one of the most pressing healthcare challenges for Society in the 21st Century.