Covalent host targeting by thioester domains of Gram-positive pathogens

细菌感染是医学和科学面临的最重要挑战之一。对几乎所有已知抗生素产生抗药性的细菌的出现对全球健康构成了威胁。人们普遍认识到对新的抗菌药物的迫切需求，但在过去几十年里引入的药物很少。为了开发与青霉素等已知药物显著不同的治疗方法，我们需要更好地了解细菌引起感染的方式。首先，细菌需要在人体内站稳脚跟。这是通过细菌表面存在的各种分子实现的。这些分子大多是专门的蛋白质，通常形成称为菌毛的毛状结构，与细菌进入人体的部位(例如喉咙、呼吸道、牙床、肠道、皮肤)发现的人类细胞结合。一旦细菌成功地附着在人类细胞上，它们要么存活并繁殖，要么通过进入细胞入侵宿主，从而最终在体内传播。如果有可能阻止细菌与人类细胞结合，就有可能在早期阶段干预感染。我们的研究发现了一种特别耐人寻味的机制，细菌可能会用它来快速且非常紧密地与人类细胞结合。这与已知的细菌结合模式相比，如强力胶和尼龙搭扣。重要的是，这种新的结合机制似乎被一些最重要的人类病原体所共享。这些细菌包括肺炎链球菌(也称为肺炎球菌)，它是英国和世界范围内肺炎的最重要原因。它还导致一种脑膜炎和败血症(血液中毒)，在发展中国家，五岁以下儿童所有可预防的死亡中有四分之一是由这种疾病引起的。肺炎球菌疾病在医院和社区中非常常见，由于细菌对许多抗生素具有抗药性，因此存在问题。其他使用超级胶状结合机制的细菌都是肺炎球菌的近亲。化脓性链球菌引起包括猩红热和链球菌咽喉炎在内的多种疾病，影响全球数亿人。这些细菌还可能导致严重的后续疾病。其中，风湿性心脏病(RHD)是印度和其他发展中国家儿童和青少年的最大杀手之一。化脓性链球菌可以像肺炎球菌一样产生抗药性，这将导致危险疾病的再次出现，如儿童床热病或风湿性心脏病。我们还预测，许多导致牙周病或牙齿脱落的细菌将能够产生超级胶蛋白，使细菌能够非常紧密地粘在牙齿表面和牙床上。我们建议研究“细菌分子超级胶水”的分子细节。我们需要确定细菌制造的关键蛋白质的准确结构，以便了解它们如何攻击人类细胞。为了实现这一目标，我们将结合两种强大的方法--核磁共振光谱和X射线结晶学--来揭示细菌蛋白质的原子细节结构。与此同时，我们将确定人类细胞的哪些成分作为细菌的结合靶标。这将通过使用细菌蛋白质作为分子诱饵，在模型人类细胞(在细胞培养中生长)上或在其中寻找它们的结合伙伴来实现。一旦确定了目标，我们将确定细菌蛋白质如何准确识别人类细胞成分。这些信息将使我们能够设计与细菌蛋白质发生特异性反应的小分子，从而形成新的诊断工具和抗菌物质的基础。我们将把我们的分子研究与使用细菌的实验相结合，以找出细菌上关键的胶水功能的丧失是否会降低它们入侵人体的效率。

Bacterial infections represent one of the most important challenges for medicine and science. The emergence of bacteria resistant to almost all known antibiotics is a threat to global health. The urgent need for new antibacterial drugs is widely recognised but very few have been introduced in the last couple of decades. In order to develop treatments that differ significantly from known drugs like penicillin we need to understand better the ways in which bacteria cause infections. To start with, bacteria need to gain a foothold in the human body. This is achieved through a variety of molecules present on the bacterial surface. These molecules, mostly specialised proteins that often form hairlike structures called pili, bind to human cells found at the site of bacterial entry into the body (e.g. throat, airways, gums, guts, skin). Once bacteria manage to cling to human cells they either survive and multiply or they invade their host by entering cells, thus eventually spreading in the body. If it was possible to prevent the bacteria from binding to human cells, it would be possible to intervene with infections at an early stage.Our research has uncovered a particularly intriguing mechanism that bacteria may use to bind rapidly and very tightly to human cells. This compares to known bacterial binding modes like superglue compares to Velcro. Importantly this new binding mechanism appears to be shared by some of the most important human pathogens. These include the bacterium Streptococcus pneumoniae (also known as pneumococcus), which is the most important cause of pneumonia in the UK and worldwide. It also causes a form of meningitis and septicaemia (blood poisoning), which in developing countries is responsible for one quarter of all preventable deaths in children under five. Pneumococcal diseases are very common in hospital settings and in the community and are problematic because the bacteria are resistant to many antibiotics. Other bacteria using the superglue-like binding mechanism are relatives of pneumococci. Streptococcus pyogenes causes a wide range of conditions including scarlet fever and strep throat, affecting hundreds of millions of people worldwide. These bacteria can also cause severe follow-on diseases. Of these, rheumatic heart disease (RHD) is one of the biggest killers of children and youths in India and other developing nations. Streptococcus pyogenes could develop antibiotic resistance just like the pneumococci did, which would result in the re-emergence of dangerous diseases like childbed fever or RHD. We also predict that many of the bacteria causing gum disease or teeth loss will be able to produce superglue proteins which may enable bacteria to very tightly stick to teeth surfaces and gums.We propose to study the molecular details of the "bacterial molecular superglue". We need to determine the precise architecture of the critical proteins made by the bacteria in order to understand how they attack human cells. To achieve this, we will use a combination of two powerful methods, NMR spectroscopy and X-ray crystallography, to reveal the structures of the bacterial proteins in atomic detail. At the same time we will determine which components of human cells serve as binding targets for the bacteria. This will be accomplished by using the bacterial proteins as molecular bait, fishing for their binding partners on or in model human cells (grown in cell culture). Once the targets have been identified we will establish how exactly the bacterial proteins recognise human cell components. This information will allow us to design small molecules that would specifically react with bacterial proteins, thus forming the basis for new diagnostic tools and antimicrobial substances. We will combine our molecular studies with experiments using bacteria in order to find out if a loss of the critical superglue function on bacteria makes them less efficient invaders of the human body.