Microneme function in toxoplasma

描述（由申请人提供）：从宿主细胞中排出是细胞内病原体（包括寄生原生动物弓形虫）生命周期中的关键步骤。T.弓形虫可在怀孕期间引起严重疾病或免疫功能障碍，并使原本健康的人的眼部病变衰弱。在细胞内复制后，寄生虫以包括疟原虫在内的其他寄生虫所共有的方式从宿主细胞中破裂。溶胞释放寄生虫感染新的宿主细胞，但随之而来的损害也助长了炎症和发烧，这是弓形虫病和疟疾的标志。我们最近发现T.弓形虫的快速排出和致命的急性疾病都依赖于孔形成蛋白TgPLP 1的及时分泌。我们的发现，TgPLP 1是从顶端微线释放暴露了这些调节分泌细胞器的新作用。TgPLP 1在排出过程中如何裂解宿主膜尚不清楚。由于缺乏这种知识，无法采取战略努力来消除其活动并改变感染过程。我们的长期目标是了解关键微线体蛋白在T。弓形虫感染该资助期的目标是确定TgPLP 1如何在出口过程中选择性地快速裂解宿主细胞膜而不引起寄生虫自我损伤。我们假设TgPLP 1孔的形成是由其靶膜的脂质组成，环境因素和蛋白质的特定结构特征决定的。这一论断是基于初步数据确定宿主脂质受体的目标选择性裂解，pH值和蛋白水解在调节孔形成的潜在作用，和保守的结构特征TgPLP 1预测驱动膜结合和寡聚化。具体目标是：（1）揭示宿主膜而不是寄生虫膜的选择性细胞溶解机制;（2）揭示TgPLP 1如何在外出期间而不是在入侵期间活跃;（3）确定快速孔形成的分子基础。通过对T.在弓形虫的生命周期中，我们期望所提出的工作将创造新的机会来中断感染和潜在地改善疾病。

DESCRIPTION (provided by applicant): Egress from host cells is a crucial step in the life cycle of intracellular pathogens including the parasitic protozoan Toxoplasma gondii. T. gondii can cause severe disease during pregnancy or immune dysfunction, and debilitating ocular pathology in otherwise healthy people. After intracellular replication, the parasite ruptures from host cells in a manner shared by other parasites including Plasmodium. Lytic egress frees the parasite to infect new host cells but the ensuing damage also fuels inflammation and fever, hallmarks of toxoplasmosis and malaria. We recently showed that T. gondii rapid egress and fatal acute disease both depend on the timely secretion of a pore-forming protein, TgPLP1. Our finding that TgPLP1 is released from apical micronemes exposed a novel role for these regulated secretory organelles. How TgPLP1 lyses host membranes during egress is not known. The absence of such knowledge precludes strategic efforts to extinguish its activity and alter the course of infection. Our long-term goal is to understand the roles of key microneme proteins in T. gondii infection. The objective for this funding period is to determine how TgPLP1 selectively and rapidly lyses host cell membranes during egress without causing parasite self-damage. We hypothesize that TgPLP1 pore formation is dictated by the lipid composition of its target membranes, environmental factors, and specific structural features of the protein. This assertion is based on preliminary data identifying host lipid receptors targeted for selective lysis, potential roles for pH and proteolysis in regulating pore formation, and conserved structural features of TgPLP1 predicted to drive membrane binding and oligomerization. The specific aims are: (1) Reveal the mechanism for selective cytolysis of host but not parasite membranes; (2) Uncover how TgPLP1 is active during egress but not during invasion; and (3) Identify the molecular basis for rapid pore formation. By providing a deeper mechanistic understanding of an essential step in the T. gondii life cycle, we expect the proposed work will create novel opportunities to interrupt infection and potentially ameliorate disease.