Global mechanisms for control of the trypanosome proteome: Defining the composition, origins and roles of cullin E3 ligases.

寄生原生动物是疾病的主要病原体，并困扰着全球人口的主要比例。从进化的角度来看，寄生虫是从宿主上高度移除的，这经常反映在支撑它们生物学的独特或不寻常机制的存在上。这一方面为理解发病机制提供了多种机会，识别治疗靶点的可能性以及对许多细胞过程的迷人的进化视角。非洲锥虫的长期生存完全依赖于抗原变异。这一过程非常成功，以至于锥虫可以感染哺乳动物宿主数月，在某些情况下可感染数年或数十年。额外的免疫逃避机制，保护寄生虫免受宿主免疫反应的先天和后天手臂组件的攻击，需要表面或内体定位蛋白。我们最近在理解支持这些免疫逃避过程的细胞生物学方面取得了三个重大进展：1.细胞表面蛋白质组的特征，揭示了与高等真核生物甚至其他锥虫如美洲锥虫的显著差异；2.证明了表面成分至少划分为四个不同的微域-表面、鞭毛袋、鞭毛和内体，其中一些蛋白质表现出这四个微域的组合；3.识别控制表面蛋白表达水平的泛素化机制的组件。这些新的见解为了解非洲锥虫独特的致病表面如何在分子水平上受到调控，以及这种调控如何对基础生物学和发病机制做出贡献开辟了一条途径。与此相结合的是利用蛋白质组学技术和最近开发的洞察力，以更全球化的方式了解锥虫细胞蛋白质组的调节。我们建议详细询问一组锥虫泛素连接酶，称为库林斯，如何在这种背景下发挥作用。泛素是蛋白质周转途径的主要介体，其中cullin基团尤其重要，因为它在表面受体周转和调节细胞周期进程中起着重要作用。鉴于锥体对基因操作的适应性、相对较小的蛋白质组大小以及强调转录后和翻译连接的机制来控制蛋白质表达水平，我们认为锥体提供了一个非常有吸引力的方法来理解这些泛素化复合体，它们的功能分层和特异性，以及它们如何促进锥体生物学和感染性。

Parasitic protozoa are major agents of disease, and afflict a major proportion of the global population. In evolutionary terms parasites are highly removed from their hosts, and this is frequently reflected in the presence of unique or unusual mechanisms that underpin their biology. This aspect presents multiple opportunities for the understanding of pathogenesis, the possibility of identifying therapeutic targets as well as offering a fascinating evolutionary perspective on many cellular processes. African trypanosomes are totally reliant on antigenic variation for their longterm survival. The process is so successful that trypanosomes can infect a mammalian host for many months and in some cases years/decades. Additional immune evasion mechanisms, which defend the parasite against components of both the innate and acquired arms of the host immune response, require surface or endosome-located proteins. We have recently made three significant advances in understanding the cell biology that underpins these immune evasion processes; 1. Characterisation of the cell surface proteome, which revealed both remarkable diversity from higher eukaryotes and even from other trypanosomatids such as American trypanosomes, 2. Demonstration of partitioning of surface components into at least four distinct micro-domains - surface, flagellar pocket, flagellum and endosome, with some proteins exhibiting a combination between all four, and 3. Identifying components of the ubiquitylation machinery that control the expression levels of surface proteins. These new insights open a route to understanding how the unique pathogenic surface of African trypanosomes is regulated at the molecular level, together with dissecting how such regulation contributes towards basic biology and pathogenesis. Coupled with this is the means to exploit proteomics technology and insights developed recently to understand in a more global manner regulation of the trypanosome cellular proteome. We propose to interrogate in detail how a group of trypanosome ubiquitin ligases, called cullins, function in this context. Ubiquitin is a major mediator of protein turnover pathways, with the cullin group especially important due to roles in surface receptor turnover and modulation of cell cycle progression. Given the amenability of the trypanosome for genetic manipulation, the comparatively small size of the proteome and the emphasis on post-transcriptional and translation-linked mechanisms to control protein expression levels, we propose that the trypanosome provides a very attractive approach to understand these ubiquitylating complexes, their functional stratification and specificity, in addition to how they contribute towards trypanosome biology and infectivity.