Structure and Function of Bacterial Toxins

1.背景：细菌利用毒力因子作为工具来帮助它们在宿主细胞上定居和寻找食物。单腺苷二磷酸核糖转移酶(MART)毒素是由多种细菌病原体产生的一大类毒力因子。许多成员是农业严重疾病的主要病原体，包括家畜的胃肠炎和呼吸道疾病、传粉者疾病以及农作物的枯萎病和赤霉病。Mart毒素是一种酶，它结合和切割NAD+中的关键键，并共价修饰宿主中的关键靶蛋白。Mart毒素对靶蛋白的共价修饰(ADP-核糖化)改变了宿主的大分子功能，并可作为活性的“开”“关”开关。2.假设：Mart毒素家族成员的结构和生化特征，包括它们的生物靶标，将为最终治疗相关细菌病原体引起的感染和疾病提供基础。3.目标：主要目标是：(I)利用生物信息学策略发现Mart毒素家族的新成员，这些新成员将通过生化/生物物理方法在结构和功能上进行表征；(Ii)在酵母模型系统中确定它们的生物靶点，为宿主与病原体的相互作用提供新的见解；以及(Iii)开发针对这些毒素的有效活性部位抑制剂，作为进一步研究的工具和未来药物发现和开发的基础。4.新颖性和意义：抗生素治疗的一种引人注目的、创新的和替代的方法是抗毒力战略，涉及针对致病病原体的毒力相关特征，而不是与生存/健康相关的特征。抗病毒剂是一种化合物，可以在不杀死细菌的情况下解除细菌的武装，从而允许受感染的宿主使用其正常的免疫系统防御来控制或消除感染。发现和设计针对MART毒素的治疗方法的能力取决于我们对这些毒素/酶的结构和反应机制的深入了解。具有匹配底物和抑制剂的一套酶结构正开始从我们的研究努力中取得成果，并将为这一重要类别的酶提供一部催化循环的虚拟电影。这些高分辨率的数据，加上我们团队为改进和开发更有效的这些毒素酶抑制剂所做的集中努力，可能会为未来开发用于预防性治疗和预防影响农业和食品的细菌性疾病的抗毒力化合物提供基础。

1. BACKGROUND: Bacteria use virulence factors as tools to aid in their colonization of host cells and in their quest for food. The mono-ADP-ribosyltransferase (mART) toxins is a large family of virulence factors produced by a wide range of bacterial pathogens. Many members are the principal causative agents in serious diseases in agriculture, including gastroenteritis and respiratory illnesses in livestock, pollinator diseases, and blight and scab diseases in crops. The mART toxins are enzymes that bind and cleave a key bond in NAD+ and covalently modify a critical target protein in the host. The covalent modification of the target protein (ADP-ribosylation) by mART toxins alters the host macromolecule function and can act as an “on” “off” switch for activity. 2. HYPOTHESIS: Structural and biochemical characterization of members of the mART toxin family, including their biological targets, will provide the basis for the eventual treatment of infections and diseases produced by the associated bacterial pathogens. 3. OBJECTIVES: The major objectives are (i) to employ a bioinformatic strategy to discover new members of the mART toxin family that will be characterized both structurally and functionally with a biochemical/biophysical approach; (ii) to identify their biological targets in a yeast model system to provide new insights on host-pathogen interactions; and (iii) to develop potent active-site inhibitors against these toxins as tools for further study and as the basis for future drug discovery and development. 4. NOVELTY AND SIGNIFICANCE: A compelling, innovative and alternative approach to antibiotic therapy is the anti-virulence strategy that involves targeting virulence-associated rather than survival/fitness-relevant traits in the offending pathogen. Anti-virulence agents are compounds that disarm bacteria without killing them, thereby allowing the infected host to use its normal immune system defenses to control or remove the infection. The ability to discover and design therapeutics against mART toxins lies in the depth of our understanding of these toxin/enzymes' structures and reaction mechanism. The suite of enzyme structures with matching substrates and inhibitors are beginning to bear fruit from our research efforts and will provide a virtual movie of the catalytic cycle for this important class of enzymes. These high-resolution data, combined with the focussed efforts of our team to improve and develop more potent inhibitors of these toxin-enzymes, may provide the basis for the future development of anti-virulence compounds for prophylactic treatment and prevention of bacterial diseases affecting agriculture and food.