Protist Oxygen Sensing in Human Disease Protist Oxygen Sensing in Human Disease

感知和响应环境中氧气的变化对于 好氧生物。后生动物通过破坏转录的稳定性来实现这一点 氧气充足时称为缺氧诱导因子(HIF)的因子。这是实现的 由一种氧依赖的4-羟基脯氨酸酶(PHD)羟化 针对泛素依赖的缺氧诱导因子-1α转录因子中的残基 蛋白酶体降解。原生动物有博士学位，但缺乏HIF，因此会做出反应 对氧气的变化有不同的反应，我们使用进化中的遥远原生生物 网盘基菌和弓形虫来解决这个问题。中国的初步研究 Dictyostelius揭示了它的PhD，DdPHYa，修改了Skp1中的一个脯氨酸，这是 是Skp1/Cullin1/F-box蛋白/Rbx1多泛素连接酶的组成部分 很复杂。Skp1脯氨酸羟化不影响其稳定性，但允许它 被一种五糖修饰，该五糖可以改变相关的F- 盒蛋白。基因组分析和生化分析证明这一点 Skp1修饰通路在原生动物寄生虫弓形虫中保守， 但不是后生动物。弓形虫先导的丧失降低了毒力 在有限的氧气和氨基酸条件下，在体内和体外生长减少。 与Dictyostelials不同，弓形虫表达第二个PhD，PHYb，这是 富氧组织定植和弓形虫生长所需的 氧气含量高。与PHYA不同，PHYB通过调节伸长来发挥作用 在蛋白质合成过程中，特别是在氧气水平升高的情况下。因为 关于弓形虫的医学重要性，我们将重点关注弓形虫，并追求三种特定的 目的：i)确定PhyA在低氧和低氨基酸条件下如何调节生长； 二)确定PHYb如何调节伸长；以及三)测试PHYa和PHYb 作为氧气感应变阻器协同工作，以在任何氧气中生长 在接触中的紧张，因为它感染宿主并导致疾病。

Sensing and responding to changes in environmental oxygen is critical for aerobic organisms. Metazoans accomplish this by destabilizing a transcription factor called hypoxia inducible factor (HIF) in oxygen sufficiency. This is achieved by an oxygen-dependent prolyl 4-hydroxylase (PHD) that hydroxylates proline residues in the HIF-1α transcription factor that targets it for ubiquitin-dependent proteasomal degradation. Protozoans have PHDs but lack HIF and thus respond to changes in oxygen differently and we use the evolutionary distant protists Dictyostelium and Toxoplasma to address this question. Initial studies in Dictyostelium revealed that its PHD, DdPHYa, modifies a proline in Skp1, which is a component of the Skp1/Cullin1/F-box protein/Rbx1 polyubiquitin ligase complex. Skp1 prolyl hydroxylation does not affect its stability, but allows it to be modified by a pentasaccharide that acts to alter the repertoire of associated F- Box proteins. Genome analysis and biochemical assays demonstrated that this Skp1 modification pathway is conserved in the protozoan parasite Toxoplasma, but not in metazoans. Loss of Toxoplasma PHYa leads decreases virulence in vivo and decreased growth in vitro under limited O2 and amino acid conditions. Unlike Dictyostelium, Toxoplasma expresses a second PHD, PHYb, which is required for colonization of oxygen rich tissues as well as Toxoplasma growth at high oxygen. In contrast to PHYa, PHYb functions by regulating elongation during protein synthesis and specifically does so at elevated O2 levels. Because of its medical importance, we will focus on Toxoplasma and pursue three specific aims: i) Determine how PHYa mediates growth at low oxygen and amino acids; ii) Define how PHYb regulates elongation; and iii) Test whether PHYa and PHYb work in tandem as an oxygen-sensing rheostat to grow in whatever oxygen tension in encounters as it infects a host and causes disease.