Abstract
Within the liver, Plasmodium sporozoites traverse cells searching for a “suitable” hepatocyte, invading these cells through a process that results in the formation of a parasitophorous vacuole (PV), within which the parasite undergoes intracellular replication as a liver stage. It was previously established that two members of the Plasmodium s48/45 protein family, P36 and P52, are essential for productive invasion of host hepatocytes by sporozoites as their simultaneous deletion results in growth-arrested parasites that lack a PV. Recent studies point toward a pathway of entry possibly involving the interaction of P36 with hepatocyte receptors EphA2, CD81, and SR-B1. However, the relationship between P36 and P52 during sporozoite invasion remains unknown. Here we show that parasites with a single P52 or P36 gene deletion each lack a PV after hepatocyte invasion, thereby pheno-copying the lack of a PV observed for the P52/P36 dual gene deletion parasite line. This indicates that both proteins are equally important in the establishment of a PV and act in the same pathway. We created a Plasmodium yoelii P36mCherry tagged parasite line that allowed us to visualize the subcellular localization of P36 and found that it partially co-localizes with P52 in the sporozoite secretory microneme organelles. Furthermore, through co-immunoprecipitation studies in vivo, we determined that P36 and P52 form a protein complex in sporozoites, indicating a concerted function for both proteins within the PV formation pathway. However, upon sporozoite stimulation, only P36 was released as a secreted protein while P52 was not. Our results support a model in which the putatively glycosylphosphatidylinositol (GPI)-anchored P52 may serve as a scaffold to facilitate the interaction of secreted P36 with the host cell during sporozoite invasion of hepatocytes.
Highlights
Malaria-causing Plasmodium parasites are responsible for taking nearly half a million lives worldwide every year (WHO, 2017)
Plasmodium yoelii parasites were genetically modified by double crossover recombination to create P36 and P52 single gene deletion mutants and a P52 P36 dual gene deletion mutant, all expressing red fluorescent protein (RFP) in their cytoplasm (Figure S1)
While all mice injected with wildtype sporozoites became blood stage patent as expected, none of the 17 mice injected with P52 sporozoites became patent, and only 2 in 17 mice injected with the P36 line became patent, the latter exhibited a patency delay of 1 day
Summary
Malaria-causing Plasmodium parasites are responsible for taking nearly half a million lives worldwide every year (WHO, 2017). Before successfully establishing a liver infection, sporozoites will traverse several cell types, including hepatocytes within transient vacuoles (TV), searching for a suitable host hepatocyte. Upon encountering such a cell, sporozoites switch to “invasion mode” and enter by creating the replication-permissive parasitophorous vacuole (PV) (Mota et al, 2001; Risco-Castillo et al, 2015). The conserved Plasmodium proteins P36 and P52 have been linked to the establishment and/or maintenance of the PV following the observation that intracellular P52 P36 dual gene deletion parasites do not display a PVM as analyzed by electron microscopy a few hours after infection (Labaied et al, 2007; Ploemen et al, 2012). The respective contributions of P52 and P36, their molecular interactions, and the mechanisms by which these proteins are involved in invasion remain unknown
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call