Protein trafficking mechanisms in the human malarial parasite P. falciparum

恶性疟原虫（热带疟疾的病原）侵入成熟的人红细胞后，将蛋白质输出到其自身质膜的边界之外，进入宿主红细胞。这些寄生虫编码的蛋白质中有许多与受感染宿主细胞的结构和生理变化有关。其中一些蛋白质是疟疾病理中的重要因素。宿主红细胞本身没有必要的分子机制将蛋白质运送到宿主细胞的最终目的地。因此，似乎寄生虫本身输出一个功能分泌系统到代谢“死亡”的宿主细胞中，这是细胞生物学中一个有趣的范例。不寻常的蛋白质靶向基序进一步强调了寄生虫分泌系统的不寻常性质。因此，可以证明，许多输出到宿主红细胞的寄生虫蛋白不具有典型的N¿末端ER靶向序列，这是进入分泌系统的先决条件。然而，这些蛋白质中的许多确实在其n端含有一个凹陷的疏水结构域。这一信号被认为可以实现分泌信号序列的功能，然而，关于这一信号如何介导内质网易位的机制数据仍然很少。在这个资助期间，我们将解决这些疏水结构域如何介导内质网易位的问题。我们设计了实验策略来进行内质网易位测定，以便从机制上剖析寄生虫早期分泌途径的初始步骤。这项研究可能揭示在其他细胞类型的内质网易位过程中发挥作用的新的内质网易位机制。此外，我们的目标是解决蛋白质的折叠状态如何影响他们的运输到宿主红细胞的细胞质。

Having invaded mature human erythrocytes, Plasmodium falciparum the aetiological agent of malaria tropica, exports proteins beyond the boundaries of its own plasma membrane, into the host erythrocyte. Many of these parasite-encoded proteins have been implicated in structural and physiological changes in the infected host cell. Some of these proteins are important factors in the pathology of malaria. The host erythrocyte does not, itself, have the necessary molecular machinery to traffic proteins to their eventual destinations in the host cell. Thus, it appears that the parasite itself exports a functional secretory system into the metabolically ¿dead¿ host cell, an interesting paradigm in cell biology. The unusual nature of the parasites secretory system is further underlined by unusual protein targeting motifs. Thus, it can be shown that many parasite proteins exported into the host erythrocyte do not possess a canonical N¿terminal ER targeting sequence, a pre-requisite for entry into the secretory system. However, many of these proteins do contain a recessed hydrophobic domain towards their N-terminal end. This signal has been suggested to fulfil the function of a secretory signal sequence, however mechanistic data on how this signal mediates ER translocation remain sparse. In this funding period, we shall address the question as to how these hydrophobic domains mediate ER translocation. We have designed experimental strategies to perform an ER translocation assay in order to mechanistically dissect the initial steps in the parasites early secretory pathway. This study may uncover novel ER translocation mechanisms playing a role in ER translocation processes in other cell types. Furthermore, we aim to address how the folding state of proteins affects their trafficking to the cytosol of the host erythrocyte.