Hammoudi Pierre-Mehdi, Maco Bohumil, Dogga Sunil Kumar, Frénal Karine, Soldati-Favre Dominique
Department of Microbiology and Molecular Medicine, CMU, Faculty of Medicine, University of Geneva, 1 Rue Michel-Servet, Geneva, 1206, Switzerland.
Mol Microbiol. 2018 Jul;109(2):225-244. doi: 10.1111/mmi.13981.
Invasion and egress are two key steps in the lytic cycle of Apicomplexa that are governed by the sequential discharge of proteins from two apical secretory organelles called micronemes and rhoptries. In Toxoplasma gondii, the biogenesis of these specialized organelles depends on the post Golgi trafficking machinery, forming an endosomal-like compartment (ELC) resembling endomembrane systems found in eukaryotes. In this study, we have characterized four phylogenetically related Transporter Facilitator Proteins (TFPs) conserved among the apicomplexans. TFP1 localises to the micronemes and ELC, TFP2 and TFP3 to the rhoptries and TFP4 to the Golgi. TFP1 crucially contributes to parasite fitness and survival while the other members of this family are dispensable. Conditional depletion of TFP1 impairs microneme biogenesis and leads to a complete block in exocytosis, which hampers gliding motility, attachment, invasion and egress. Morphological investigations revealed that TFP1 participates in the condensation of the microneme content, suggesting the transport of a relevant molecule for maintaining the intraluminal microenvironment necessary for organelle maturation and exocytosis. In absence of TFP2, rhoptries adopt a considerable elongated shape, but the abundance, processing or secretion of the rhoptry content are not affected. These findings establish the relevance of TFPs in organelle maturation of T. gondii.
入侵和逸出是顶复门原虫裂解周期中的两个关键步骤，这两个步骤由来自两种顶端分泌细胞器（微线体和棒状体）的蛋白质顺序释放所控制。在刚地弓形虫中，这些特殊细胞器的生物发生依赖于高尔基体后运输机制，形成一个类似于真核生物内膜系统的类内体区室（ELC）。在本研究中，我们鉴定了顶复门原虫中保守的四种系统发育相关的转运促进蛋白（TFP）。TFP1定位于微线体和ELC，TFP2和TFP3定位于棒状体，TFP4定位于高尔基体。TFP1对寄生虫的适应性和生存至关重要，而该家族的其他成员则是可有可无的。条件性缺失TFP1会损害微线体的生物发生，并导致胞吐作用完全受阻，从而阻碍滑行运动、附着、入侵和逸出。形态学研究表明，TFP1参与微线体内容物的浓缩，提示其运输一种相关分子以维持细胞器成熟和胞吐作用所需的腔内微环境。在缺乏TFP2的情况下，棒状体呈现出相当长的形状，但棒状体内容物的丰度、加工或分泌不受影响。这些发现确立了TFP在刚地弓形虫细胞器成熟中的相关性。
