Peptidoglycan release and recycling in pathogenic mycobacteria.

联合国和世卫组织都认识到结核病（TB）是贫困的主要驱动因素，这种疾病的耐药形式导致高死亡率。耐药菌株的治疗选择很差，结核病感染因经常与艾滋病毒合并感染而变得更加复杂。这些因素导致去年约180万人死于结核病。尽管全球作出了努力，但这一问题只会越来越严重。报告的结核病病例对利福平（一种一线抗生素）耐药的比例从2015年的31%上升到2016年的41%。这是一个抗生素耐药性危机，迫切需要新的治疗选择。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β-内酰胺类抗生素具有内源性广谱β-内酰胺酶，因此β-内酰胺类抗生素尚未用于结核病治疗。最近的研究，包括一项临床试验，改变了这一观点。当与β-内酰胺酶抑制剂组合时，β-内酰胺抗生素表现与现有疗法一样好。尽管如此，我们对结核分枝杆菌的最终靶点肽聚糖的代谢以及结核分枝杆菌如何代谢肽聚糖知之甚少。结核病使用PG来调节宿主免疫系统。M.结核病是结核病的病原体，并产生细菌中最复杂的细胞壁之一。分枝杆菌细胞壁由三个主要层组成，包括肽聚糖、阿拉伯半乳聚糖和分枝菌酸。复杂的细胞壁对生长和分裂产生限制，这必须通过在分裂期间仔细重塑细胞壁或插入跨包膜结构来克服。这一过程必然导致小分子代谢物的产生，已知这些代谢物可被免疫系统识别。肽聚糖是长多糖与通过短肽交联的重复二糖单元的组合。这种网状结构赋予生物体形状，并保护其免受多种压力。在我的BBSRC未来领袖奖学金，我已经表明，分枝杆菌在生长过程中产生两种不同形式的肽聚糖片段作为一种新的肽聚糖回收系统的结果。免疫刺激性二糖-肽缀合物激活宿主NOD受体，而剥离其茎肽的二糖作为细菌自身的信号，驱动生长和抗生素抗性。肽聚糖代谢可以被认为是一个循环，与合成，重塑，降解和回收密切相关。在这个BBSRC大卫菲利普斯奖学金，我将遗传和生化解剖这些途径使用多学科的方法。通过采用公正的遗传筛选和我们的身体的感知肽聚糖片段的能力，我将首次揭示致病性分枝杆菌中肽聚糖干肽回收的遗传和机制基础。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且可药用的途径，其长期目标是减少抗生素耐药性的负担。

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.