How does the trypanosome haptoglobin-hemoglobin receptor interact with nutrients and immunity molecules? Receptor structure to cellular mechanism.

锥虫是单细胞寄生虫，在撒哈拉以南非洲地区引起重大疾病。它们感染人类，引起非洲昏睡病。它们也感染各种家畜，包括牛，导致降低食物生产能力的疾病。锥虫在人类或动物宿主的血液中生活和分裂。为了在这种环境中生存，它们具有高度适应的细胞表面。这使它们能够从血液中摄取营养分子，它们可以在生长和分裂时将其用作能量来源或建筑材料。然而，这也使他们处于危险之中。如果它们被抗体识别，它们可以被人体的免疫防御系统检测和破坏。人体还含有几种称为锥虫分解因子的蛋白质复合物。如果被寄生虫吸收，这些会导致锥虫破裂和死亡。能够感染人类的锥虫种类已经发展出避免锥虫溶解因子摄取或阻断导致溶解的过程的方法。锥虫如何既从血液中摄取营养分子又避免被抗体识别？它们被一种叫做VSG的蛋白质外壳所覆盖。该涂层是动态的，VSG分子与附着的抗体一起被吸收到细胞中。抗体被降解，VSG返回到表面。寄生虫有能力表达大量不同的VSG分子，它们可以切换使用哪种VSG来避免被免疫系统检测到。用于吸收营养分子的受体蛋白必须在VSG层的背景下结合它们的货物，同时避免被免疫系统识别。在这个提议中，我们将使用各种不同的实验工具来研究这些受体之一-结合珠蛋白-血红蛋白受体（HpHbR）。这种受体是寄生虫冲突的核心。它参与将HpHb摄取到锥虫细胞中，寄生虫从锥虫细胞中获得血红素分子，使其能够构建自己的细胞结构。但它也是一个主要的途径为锥虫溶解因子的摄取，导致寄生虫death.We将使用结构生物学方法来了解，在分子细节，受体如何识别其不同的货物，包括Hp血红蛋白和锥虫溶解因子。我们将联合收割机与细胞生物学相结合，使我们能够了解在寄生虫表面的背景下，配体摄取是如何发生的。这将是第一项结合结构和细胞实验以深入了解锥虫受体的研究，揭示锥虫表面如何适应营养吸收，同时避免被身体破坏。它还将显示毒素分子的摄取途径如何发挥作用。这是天然锥虫分解因子目前使用的途径，并且有可能被颠覆，以允许药物和毒素分子特异性地针对这种致命的寄生虫。

Trypanosomes are single celled parasites that cause significant disease in Sub Saharan Africa. They infect humans, causing African sleeping sickness. They also infect a variety of domestic animals, including cattle, leading to disease that reduces food production capability.Trypanosomes live and divide in the blood of their human or animal host. To survive in this environment they have a highly adapted cell surface. This allows them to take up nutrient molecules from the blood, which they can use as sources of energy or building materials as they grow and divide. However, it also puts them in peril. If they are recognised by antibodies, they can be detected and destroyed by the body's immune defences.The human body also contains several protein complexes called trypanolytic factors. If taken up into the parasite, these cause trypanosomes to burst and die. Species of trypanosome that can infect humans have developed ways to avoid trypanolytic factor uptake or to block the process that leads to lysis.How do the trypanosomes both take up nutrient molecules from the blood and to avoid recognition by antibodies? They are covered by a coat of a protein called VSG. This coat is dynamic with VSG molecules being taken up into the cell together with attached antibodies. The antibodies are degraded and the VSG returned to the surface. The parasite has the ability to express a large number of different VSG molecules, and they can switch which VSG they use to avoid detection by the immune system. The receptor proteins that are used to take up nutrient molecules must bind their cargos in the context of this VSG layer and yet avoid recognition by the immune system.In this proposal we will use a variety of different experimental tools to study one of these receptors - the haptoglobin-haemoglobin receptor (HpHbR). This receptor lies at the heart of a conflict for the parasite. It is involved in the uptake of HpHb into the trypanosome cell, from which the parasite obtains haem molecules to allow it to build its own cellular structures. But it is also a major route for the uptake of trypanolytic factors, leading to parasite death.We will use structural biology methods to understand, in molecular detail, how the receptor recognises its different cargos, including HpHb and trypanolytic factors. We will combine this with cell biology, allowing us to understand how ligand uptake occurs in the context of the parasite surface. This will be the first study that combines structural and cellular experiments to gain insight into a trypanosome receptor, revealing how the trypanosome surface is adapted to allow nutrient uptake while avoiding destruction by the body. It will also show how an uptake route for a toxin molecules functions. This is a route currently used by natural trypanolytic factors and has the potential to be subverted to allow drug and toxin molecules to be specifically targeted to this deadly parasite.