Autophagy is a lysosome-dependent degradative process involving over 35 Atg proteins. The autophagy repertoire in malaria parasites is limited and does not appear to be a major degradative process. To better understand the autophagy process, we investigated Plasmodium falciparum Atg18 (PfAtg18), a PROPPIN family protein, whose members like S. cerevisiae Atg18 (ScAtg18) and human WIPI2 are essential for autophagy. Wild type and mutant PfAtg18 were expressed in P. falciparum and assessed for localization, the effect of various inhibitors and antimalarials on PfAtg18 localization, and identification of PfAtg18-interacting proteins. PfAtg18 is expressed in asexual erythrocytic stages and localized to the food vacuole, which was also observed with other Plasmodium Atg18 proteins, indicating that food vacuole localization is a conserved feature. Interaction of PfAtg18 with the food vacuole-associated PI3P is essential for localization, as PfAtg18 mutants of PI3P-binding motifs neither bound PI3P nor localized to the food vacuole. Interestingly, ScAtg18 showed complete cytoplasmic localization despite binding with PI3P, indicating additional requirement for PfAtg18 localization. The food vacuole multi-drug resistance protein 1 (MDR1) was consistently identified in the PfAtg18 immunoprecipitate, and also interacted with PfAtg18. In contrast to PfAtg18, ScAtg18 did not interact with the MDR1, which, in addition to PI3P, could play a critical role in localization of PfAtg18. Chloroquine and amodiaquine greatly affected PfAtg18 localization, suggesting that these quinolines target PfAtg18 or the proteins that might be involved in its localization. Thus, PI3P and MDR1are critical mediators of PfAtg18 localization, and PfAtg18 may modulate MDR1 activity.

中文翻译：

---

恶性疟原虫Atg18通过与多药抗性蛋白1和磷脂酰肌醇3-磷酸的相互作用而定位于食物液泡

自噬是一种依赖溶酶体的降解过程，涉及超过35种Atg蛋白。疟原虫的自噬库是有限的，并且似乎不是主要的降解过程。为了更好地了解自噬过程，我们研究了PROPPIN家族蛋白恶性疟原虫Atg18（PfAtg18），其成员如酿酒酵母Atg18（ScAtg18）和人WIPI2对于自噬至关重要。在恶性疟原虫中表达野生型和突变体PfAtg18，并评估其定位，各种抑制剂和抗疟药对PfAtg18定位的影响以及鉴定与PfAtg18相互作用的蛋白质。PfAtg18在无性红细胞生成阶段表达并定位于食物液泡，其他疟原虫Atg18蛋白也观察到PfAtg18，表明食物液泡的定位是保守的。PfAtg18与与食物液泡相关的PI3P的相互作用对于定位至关重要，因为PI3P结合基序的PfAtg18突变体既不与PI3P结合也不定位于食物液泡。有趣的是，尽管与PI3P结合，ScAtg18仍显示出完整的胞质定位，表明对PfAtg18定位的额外要求。在PfAtg18免疫沉淀物中始终鉴定出食品液泡多药抗性蛋白1（MDR1），并且还与PfAtg18相互作用。与PfAtg18相比，ScAtg18不与MDR1相互作用，MDR1除PI3P外还可以在PfAtg18的定位中发挥关键作用。氯喹和氨二喹极大地影响了PfAtg18的定位，表明这些喹啉靶向PfAtg18或可能参与其定位的蛋白质。从而，