Structure and Function of the Trypanosome Flagellar Membrane

在原生动物寄生虫克氏锥虫和布鲁氏锥虫的鞭毛中发现了许多密切相关的钙结合蛋白：克氏锥虫的鞭毛钙结合蛋白（FCaBP）为24 kDa，布鲁氏锥虫的钙结合蛋白家族为24 kDa （Tb-24）、25 kDa （Tb-17）和44 kDa （Tb-44）钙蛋白。这些蛋白质通过在其氨基末端添加肉豆蔻酸酯和棕榈酸酯进行修饰，从而介导鞭毛膜的定位。在上一个资助期间，已确定了calflins的各种特性：(i)它们与钙结合并经历钙诱导的构象变化，（ii）它们在鞭毛膜上的定位取决于膜固醇的浓度，（iii）它们似乎通过钙依赖结合和伴侣蛋白的假设调节发挥作用，（iv）它们具有独特的三维结构，与钙调蛋白相似但不同，(v)它们是鞭毛内运输（IFT）装置的组成部分和/或底物。此外，从这项工作中产生的相关发现包括：(1)鞭毛膜在化学上与膜膜不同，在脂筏中显示出高度的液体秩序和富集；(2)鞭毛DnaJ （hsp40）蛋白参与细胞壁的生物发生；(3)鞘脂合成对正常的细胞分裂和细胞器分离至关重要。我们对FCaBP和calflagins的研究已经开始阐明这些蛋白在鞭毛功能和生物发生中的功能，并揭示了鞭毛膜作为双酰化蛋白募集和参与IFT的新平台。来自同事的信息表明，这些基本特性可能是所有纤毛结构（鞭毛和感觉纤毛）所共有的，因此锥虫可能是确定纤毛功能的一个强大的模型系统。我们建议用五年的时间来扩展我们对这些蛋白质和鞭毛膜的研究，有以下具体目标：(1)定义鞭毛蛋白靶向的分子决定因素。(2)研究鞭毛内运输与鞭毛膜运输之间的相互作用。(3)确定鞭毛膜的脂质组成及其对蛋白质靶向的贡献。

DESCRIPTION (provided by applicant): Structure and Function of the Trypanosome Flagellar Membrane A number of closely related calcium-binding proteins are found in the flagella of the protozoan parasites Trypanosoma cruzi and Trypanosoma brucei: a 24 kDa flagellar calcium binding protein (FCaBP) of T. cruzi and a family of 24 kDa (Tb-24), 25 kDa (Tb-17), and 44 kDa (Tb-44) calfagin proteins of Trypanosoma brucei. These proteins are modified by the addition of myristate and palmitate at their amino termini, which mediate localization to the flagellar membrane. Various properties of the calflagins have been determined during the previous funding period: (i) they bind calcium and undergo calcium-induced changes in conformation, (ii) their localization to the flagellar membrane is dependent on the concentration of membrane sterols, (iii) they appear to function through the calcium-dependent binding and presumed regulation of partner proteins, (iv) they have unique three-dimensional structures that are similar to but distinct from calmodulin and (v) they are components of and/or substrates for the intraflagellar transport (IFT) apparatus. Additional, related discoveries arising from from this work include the following: (i) the flagellar membrane is chemically distinct from the pellicular membrane and shows a high degree of liquid order and enrichment in lipid rafts, (ii) a flagellar DnaJ (hsp40) protein is involved in the biogenesis of the cytostome and (iii) sphingolipid synthesis is essential for normal cytokinesis and organelle segregation in T. brucei. Our work on FCaBP and the calflagins has begun to illuminate the functions of these proteins in flagellar function and biogenesis and has revealed the flagellar membrane as a novel platform for the recruitment of dually acylated proteins and participation in IFT. Information from colleagues indicate that these basic properties may be common to all ciliary structures (flagella and sensory cilia) and thus the trypanosome may be a powerful model system for the determination of ciliary function generally. We propose to extend our studies of these proteins specifically and the flagellar membrane generally in a five-year research effort having the following Specific Aims: (1) To define the molecular determinants of flagellar protein targeting. (2) To examine the interaction between intraflagellar transport and flagellar membrane trafficking. (3) To determine the lipid composition of the flagellar membrane and its contribution to protein targeting. PUBLIC HEALTH RELEVANCE: Over 200 million people are at risk of infection Trypanosoma cruzi, the parasitic agent of Chagas disease and Trypanosoma brucei, the agent of African sleeping sickness. The drugs available for treating trypanosome infections are not very effective and suffer from poor efficacy and high toxicity. Our studies are aimed at identifying novel process of trypanosome cell biology that can be exploited for the development of new drugs for Chagas disease and African sleeping sickness. Further, our proposed studies of flagellar- ciliary membrane targeting are relevant to many human diseases, collectively known as the "ciliopathies." The ciliopathies cause kidney disease, diabetes, cancer, developmental disorders, and blindness, and some of these human diseases are likely to be caused by defects in the processes we are studying in this research project.