Structural Analysis of PfSec62-Autophagy Interacting Motifs (AIM) and PfAtg8 Interactions for Its Implications in RecovER-phagy in Plasmodium falciparum

A Potent Kalihinol Analogue Disrupts Apicoplast Function and Vesicular Trafficking in P. falciparum Malaria

Here we report the discovery of MED6-189, a new analogue of the kalihinol family of isocyanoterpene (ICT) natural products. MED6-189 is effective against drug-sensitive and -resistant P. falciparum strains blocking both intraerythrocytic asexual replication and sexual differentiation. This compound was also effective against P. knowlesi and P. cynomolgi. In vivo efficacy studies using a humanized mouse model of malaria confirms strong efficacy of the compound in animals with no apparent hemolytic activity or apparent toxicity. Complementary chemical biology, molecular biology, genomics and cell biological analyses revealed that MED6-189 primarily targets the parasite apicoplast and acts by inhibiting lipid biogenesis and cellular trafficking. Genetic analyses in P. falciparum revealed that a mutation in PfSec13, which encodes a component of the parasite secretory machinery, reduced susceptibility to the drug. The high potency of MED6-189 in vitro and in vivo, its broad range of efficacy, excellent therapeutic profile, and unique mode of action make it an excellent addition to the antimalarial drug pipeline.

The role of electrostatic potential in the translocation of triangulene across membranes

Triangulene and its derivatives show broad application prospects in the fields of biological imaging and biosensing. However, its interaction with cell membranes is still poorly studied. In this study, classical molecular dynamics simulations were used to adjust the electrostatic potential of triangulene to observe its interactions with cell membranes. We found that electrostatic potential not only affects the behavior as it enters the cell membrane, but also spatial distribution within the cell membrane. The angle distribution of inside-0 and all-0 triangulene when penetrating the membrane is more extensive than that of ESP triangulene. However, inside-0 triangulene could cross the midline of the cell membrane and prefers to stay in the upper leaflet, while all-0 triangulene and ESP triangulene can reach the lower leaflet. These findings can help us regulate the distribution of nanoparticles in cells, so as to design functional nanoparticles that conform to the requirements.

Autophagy Underlies the Proteostasis Mechanisms of Artemisinin Resistance in P. falciparum Malaria

Emerging resistance to artemisinin (ART) has become a challenge for reducing worldwide malaria mortality and morbidity. The C580Y mutation in Plasmodium falciparum Kelch13 has been identified as the major determinant for ART resistance in the background of other mutations, which include the T38I mutation in autophagy-related protein PfATG18. Increased endoplasmic reticulum phosphatidylinositol-3-phosphate (ER-PI3P) vesiculation, unfolded protein response (UPR), and oxidative stress are the proteostasis mechanisms proposed to cause ART resistance. While UPR and PI3P are known to stimulate autophagy in higher organisms to clear misfolded proteins, participation of the parasite autophagy machinery in these mechanisms of ART resistance has not yet been experimentally demonstrated. Our study establishes that ART-induced ER stress leads to increased expression of P. falciparum autophagy proteins through induction of the UPR. Furthermore, the ART-resistant K13^C580Y isolate shows higher basal expression levels of autophagy proteins than those of its isogenic counterpart, and this magnifies under starvation conditions. The copresence of PfK13 with PfATG18 and PI3P on parasite hemoglobin-trafficking vesicles demonstrate interactions between the autophagy and hemoglobin endocytosis pathways proposed to be involved in ART resistance. Analysis of PfK13 mutations in 2,517 field isolates, revealing an impressive >85% coassociation between PfK13 C580Y and PfATG18 T38I, together with our experimental studies with an ART-resistant P. falciparum strain establishes that parasite autophagy underpins various mechanisms of ART resistance and is a starting point to further explore this pathway for developing antimalarials.