Essential role for PfHSP40 in asexual replication and thermotolerance of malaria parasites.

Plasmodium falciparum, the parasite responsible for nearly all cases of severe malaria, must survive challenging environments to persist in its human host. Symptomatic malaria is characterized by periodic fevers corresponding to the 48-hour asexual reproduction of P. falciparum in red blood cells. As a result, P. falciparum has evolved a diverse collection of heat shock proteins to mitigate the stresses induced by temperature shifts. Among the assortment of heat shock proteins in P. falciparum, there is only one predicted canonical cytosolic J-domain protein, PfHSP40 (PF3D7_1437900). Here, we generate a PfHSP40 tunable knockdown strain of P. falciparum to investigate the biological function of PfHSP40 during the intraerythrocytic lifecycle. We determine that PfHSP40 is required for malaria parasite asexual replication and survival of febrile temperatures. Previous reports have connected proteotoxic and thermal stress responses in malaria parasites. However, we find PfHSP40 has a specific role in heat shock survival and is not essential for mitigating the proteotoxic stresses induced by artemisinin or proteosome inhibition. Following PfHSP40 knockdown, malaria parasites have a cell cycle progression defect and reduced nuclear replication. Untargeted proteomics reveal PfHSP40 depletion leads to a multifaceted downregulation of DNA replication and repair pathways. Additionally, we find PfHSP40 knockdown sensitizes parasites to DNA replication inhibition. Overall, these studies define the specialized role of the J-domain protein PfHSP40 in malaria parasites during the blood stages of infection.