Peptidoglycan release and recycling in pathogenic mycobacteria.

联合国和世卫组织都承认结核病(TB)是贫困的主要驱动力，这种疾病的耐药性导致了高死亡率。耐药菌株的治疗选择很差，频繁与艾滋病毒合并感染加剧了结核病感染。这些因素导致去年约180万人死于结核病。尽管全球都在努力，但这个问题只会变得更糟。据报告对一线抗生素利福平耐药的结核病病例比例从2015年的31%上升到2016年的41%。这是一场抗生素耐药性危机，迫切需要新的治疗方案。解决这一危机的最有效方法之一是恢复现有药物。多年来，由于其内源性广谱β-内酰胺酶，β-内酰胺类抗生素一直未用于结核病的治疗。最近的研究，包括一项临床试验，已经改变了这种观点。当与β-内酰胺酶抑制剂联合使用时，β-内酰胺类抗生素的效果与现有疗法一样好。尽管如此，我们对它们的最终目标--结核分枝杆菌中的肽聚糖的新陈代谢，或者结核分枝杆菌如何利用PG调节宿主免疫系统，知之甚少。结核分枝杆菌是结核病的病原体，并产生细菌中最复杂的细胞壁之一。分枝杆菌细胞壁主要由三层组成，包括肽聚糖、阿拉伯半乳聚糖和分枝杆菌酸。复杂的细胞壁对生长和分裂造成限制，必须通过在分裂过程中仔细重塑细胞壁或插入包膜跨越结构来克服这一点。这个过程必然导致小分子代谢物的产生，这是已知的免疫系统识别的。肽聚糖是由长多糖和重复的双糖单元通过短肽交联而成的组合。这种网状结构赋予了有机体形状，并保护它免受无数压力。在我的BBSRC未来领袖奖学金期间，我证明了分枝杆菌在生长过程中会产生两种不同形式的肽聚糖片段，这是一种新颖的肽聚糖循环系统的结果。免疫刺激的双糖-多肽结合物激活宿主的NOD受体，而去除茎多肽的双糖则是细菌本身驱动生长和抗生素耐药性的信号。多肽的代谢可以被认为是一个循环，合成、重塑、降解和回收密切相关。在BBSRC David Phillips奖学金中，我将使用多学科方法从遗传学和生物化学角度剖析这些途径。通过使用无偏见的基因筛查和我们身体感知肽聚糖片段的能力，我将首次揭示致病分枝杆菌中肽聚糖干肽循环的遗传和机制基础。我将继续剖析肽聚糖生物合成、重塑和降解的分子基础，以便我们更好地了解分枝杆菌中这一重要和可药物的途径，长期目标是减少抗菌素耐药性的负担。

The UN and WHO have both recognised tuberculosis (TB) as a major driver of poverty with drug-resistant forms of the disease causing high mortality rates. Drug-resistant strains have poor treatment options, and TB infection is compounded by frequent co-infection with HIV. These factors contributed to TB killing approximately 1.8 million people last year. Despite global efforts, this problem is only getting worse. The percentage of TB cases reported to be resistant to rifampicin, a front-line antibiotic rose from 31% in 2015 to 41% in 2016. This is an antibiotic resistance crisis and new therapeutic options are urgently needed. One of the most efficient ways to address this crisis is to rehabilitate existing medicines. For years beta-lactam antibiotics have not been used in TB treatment due to its endogenous broad-spectrum beta-lactamase. Recent studies, including a clinical trial have changed this view. When combined with a beta-lactamase inhibitor, beta-lactam antibiotics perform as well as existing therapeutics. Despite this, we know relatively little about the metabolism of their either eventual target, peptidoglycan in Mycobacterium tuberculosis, or how M. tuberculosis uses PG to modulate the host immune system. M. tuberculosis is the causative agent of the TB and generates one of the most complex cell walls amongst bacteria. The mycobacterial cell wall is comprised of three main layers including peptidoglycan, arabinogalactan and mycolic acids. A complex cell wall creates constraints on growth and division, which must be overcome through careful remodelling of the cell wall during division or the insertion of envelope spanning structures. This process necessarily leads to the production of small molecule metabolites, which are known to be recognised by the immune system. Peptidoglycan is a combination of long polysaccharides with a repeating disaccharide unit cross-linked through short peptides. This mesh-like structure gives the organism shape and protects it from numerous stresses. During my BBSRC Future Leader Fellowship, I have shown that mycobacteria generate two distinct forms of peptidoglycan fragments during growth as a consequence of a novel peptidoglycan recycling system. Immunostimulatory disaccharide-peptide conjugates activate host NOD receptors, while disaccharides stripped of their stem peptide serve as signals to the bacterium itself driving growth and antibiotic resistance.Peptidoglycan metabolism can be thought of as a cycle, with synthesis, remodelling, degradation and recycling intimately associated. In this BBSRC David Phillips Fellowship I will genetically and biochemically dissect these pathways using a multi-disciplinary approach. By employing unbiased genetic screens and our body's ability to sense peptidoglycan fragments I will uncover for the first time the genetic and mechanistic basis of peptidoglycan stem-peptide recycling in pathogenic mycobacteria. I will go on to dissect the molecular basis of peptidoglycan biosynthesis, remodelling and degradation so that we might better understand this important and druggable pathway in mycobacteria, with the long-term aim of reducing the burden of antimicrobial resistance.