Developing constrained peptides as UBL-pathway antimalarials

疟疾是一种主要的热带和亚热带疾病，据世界卫生组织（WHO）估计，每年约有43万至45万人死于疟疾。另据估计，90多个国家每年约有2.15亿例疟疾病例。这种疾病是由单细胞真核寄生虫疟原虫引起的，其中恶性疟原虫是感染人类的最致命和最突出的物种。疟原虫有一个二遗传的生命周期，分为哺乳动物和按蚊宿主。有一系列药物可用于治疗疟疾感染者，但疟原虫物种对这些当前治疗的耐药性增加是全球关注的问题。本项目的目的是研究限制性肽是否可以作为一种新的抗疟疾治疗形式。肽的靶点是PfUCHL 3，一种恶性疟原虫必需的和充分表征的去泛素化酶（DUB）。DUB参与从蛋白质中去除泛素，并且可以改变细胞内靶向蛋白质的命运和功能。PfUCHL 3非常适合于体外研究，因为它可以被纯化到高浓度和纯度，此外，PfUCHL 3单独和与泛素探针（Ub-VME）复合的晶体结构已经得到解决。抑制泛素-PfUCHL 3蛋白质-蛋白质相互作用预期是细胞致死的，并且使用约束肽来这样做具有许多优点。它还有助于硬化其结构，使其更具蛋白酶抗性，并有助于增加其结合亲和力和细胞渗透性。本项目中的肽将通过环化、肽钉合或通过使用支架蛋白来限制。该项目的主要目的是产生和生物免疫学上鉴定可以结合并潜在抑制PfUCHL 3的限制性肽库。

Malaria is a major tropical and sub-tropical disease which was estimated by the World Health Organisation (WHO) to be responsible for the deaths of around 430,000 - 450,000 people annually. It is also estimated that there are around 215 million cases of malaria annually spanning over 90 countries. The disease is caused by the unicellular eukaryotic parasite Plasmodium, of which Plasmodium falciparum is the most deadly and prominent of the species to infect humans. Plasmodium has a digenetic life cycle which is split between a mammalian and a anopheles mosquito host. There are a range of medications available to treat malaria infected individuals but increasing drug resistance of Plasmodium species to these current treatments is of global concern. The aim of this project will be to investigate whether constrained peptides can be used as a new form of anti-malarial treatment.The target of the peptides is PfUCHL3, an essential and well characterised deubiquitinating enzyme (DUB) of P. falciparum. DUBs are involved in the removal of ubiquitin from proteins and can alter the targeted proteins fate and function within the cell. PfUCHL3 is well suited to in-vitro studies because it can be purified to high concentrations and purity, furthermore crystal structures of PfUCHL3 alone and in complex with a ubiquitin probe (Ub-VME) have been solved. Inhibiting the ubiquitin-PfUCHL3 protein-protein interaction is expected to be cell lethal and using constrained peptides to do so has many advantages.Constraining a peptide helps lock it into its bioactive, binding-competent conformation. It also helps rigidify its structure, make it more protease resistant and helps increase its binding affinity and cell permeability. Peptides in this project will be constrained by either cyclisation, peptide stapling or by using scaffold proteins. The main aim of this project is to generate and biophysically characterise a library of constrained peptides which can bind to and potentially inhibit PfUCHL3.