Impact of telomere-associated protein complexes on VSG expression site regulation and structure in Trypanosoma brucei

原生病原体布鲁氏锥虫是撒哈拉以南非洲人类昏睡病和家畜纳加纳等致命疾病的病原体。在其生命周期中，锥虫必须在哺乳动物宿主和采采蝇载体之间穿梭。在哺乳动物宿主中，布氏毛滴虫血液形成细胞(BSF)的免疫逃逸依赖于抗原变异，包括单等位基因表达和变异表面糖蛋白(VSG)基因的周期性切换。活性VSG总是从仅有的15个亚端粒表达位点(ES)中的一个转录而来，端粒相关蛋白被证明调节这些位点的表达和重组事件。在从BSF向昆虫驻留原环型(PCF)分化的过程中，活性ES转录沉默。调节抗原变异的确切分子机制仍然不清楚，因为到目前为止只有几个端粒相关蛋白被鉴定和鉴定。我们使用定量相互作用组分来确定布氏毛滴虫端粒蛋白复合体的组成，并鉴定了17个端粒相关蛋白，其中包括已经证实的端粒蛋白。在这项拨款提案中，我们建议两个独立但互补的项目来表征新的端粒相关蛋白，并阐明它们在抗原变异和端粒维持中的假定功能。初步数据已经表明，这两种寄生虫的端粒复合体组成不同。为了验证我们的定量相互作用方法，我们已经证明了一种新的端粒结合蛋白TelAP1与端粒蛋白TRF、RAP1和TIF2形成复合体，并影响发育分化过程中ES沉默的动力学。

The protist pathogen, Trypanosoma brucei, is the causative agent of fatal diseases such as sleeping sickness in humans and nagana in livestock in sub-Saharan Africa. During their life cycle, trypanosomes have to shuttle between a mammalian host and the tsetse fly vector. In the mammalian host, immune evasion of T. brucei bloodstream form cells (BSF) relies on antigenic variation, which includes monoallelic expression and periodic switching of variant surface glycoprotein (VSG) genes. The active VSG is always transcribed from one of only 15 subtelomeric expression sites (ESs) and telomere-associated proteins have been shown to regulate expression and recombination events at these sites. During differentiation from BSF to the insect-resident procyclic form (PCF), the active ES is transcriptionally silenced. The exact molecular mechanisms that regulate antigenic variation are still elusive because only a few telomere-associated proteins have been identified and characterized so far.We used quantitative interactomics to determine the composition of telomere protein complexes in T. brucei and identified 17 telomere-associated proteins including already validated telomeric proteins. In this grant proposal, we suggest two independent but complementary projects to characterise novel telomere-associated proteins and elucidate their putative function in antigenic variation and telomere maintenance. Preliminary data already suggest different telomere complex compositions in the two forms of the parasite. To validate our quantitative interactomics approach, we could already show that one of the novel telomere-binding proteins, TelAP1, forms a complex with telomeric proteins TRF, RAP1 and TIF2 and influences ES silencing kinetics during developmental differentiation.