Apical Surface Expression of Aspartic Protease Plasmepsin 4, a Potential Transmission-blocking Target of the Plasmodium Ookinete

Abstract

To invade its definitive host, the mosquito, the malaria parasite must cross the midgut peritrophic matrix that is composed of chitin cross-linked by chitin-binding proteins and then develop into an oocyst on the midgut basal lamina. Previous evidence indicates that Plasmodium ookinete-secreted chitinase is important in midgut invasion. The mechanistic role of other ookinete-secreted enzymes in midgut invasion has not been previously examined. De novo mass spectrometry sequencing of a protein obtained by benzamidine affinity column of Plasmodium gallinaceum ookinete axenic culture supernatant demonstrated the presence of an ookinete-secreted plasmepsin, an aspartic protease previously only known to be present in the digestive vacuole of asexual stage malaria parasites. This plasmepsin, the ortholog of Plasmodium falciparum plasmepsin 4, was designated PgPM4. PgPM4 and PgCHT2 (the P. gallinaceum ortholog of P. falciparum chitinase PfCHT1) are both localized on the ookinete apical surface, and both are present in micronemes. Aspartic protease inhibitors (peptidomimetic and natural product), calpain inhibitors, and anti-PgPM4 monoclonal antibodies significantly reduced parasite infectivity for mosquitoes. These results suggest that plasmepsin 4, previously known only to function in the digestive vacuole of asexual blood stage Plasmodium, plays a role in how the ookinete interacts with the mosquito midgut interactions as it becomes an oocyst. These data are the first to delineate a role for an aspartic protease in mediating Plasmodium invasion of the mosquito and demonstrate the potential for plasmepsin 4 as a malaria transmission-blocking vaccine target.

New Ultrastructural Analysis of the Invasive Apparatus of the Plasmodium Ookinete

“…For example, it has been shown that not only surface proteins, such as P25 and P28 family proteins, but also ookinete-secreted proteins may synergize as transmissionblocking vaccine targets. 10,12 To this end, new methods to study the ultrastructure of Plasmodium ookinetes may provide new insights into how to interfere with the biology of malaria parasites to the goal of malaria control. 13 Here, we show new transmission electron microscope morphologies of developing and mature ookinete stages of P. gallinaceum.…”

Toxoplasma gondii aspartic protease 1 is not essential in tachyzoites

“…PMIV, which was previously only demonstrated to function in the food vacuole of asexual stages, was recently localized to the micronemes and at the apical surface of ookinetes. A second role for PMIV is suspected in mosquito midgut invasion and/or development of oocysts from ookinetes (Li et al, 2010). Most recently, PfPMV has been localized to the endoplasmic reticulum (ER) and was demonstrated to be essential for parasite viability and hence represents a new target for therapeutic intervention against malaria.…”

The Impact of Antiretroviral Therapy on Malaria Parasite Transmission

“…Accordingly, the first-line ART containing the PIs LPV/r had the strongest impact on oocyst intensity in vivo (Figures 3E,G). Although, to the best of our knowledge, the effect of ARVs on ookinetes has not been previously reported, it is known that PMs IV, VII, and X (Li et al, 2010(Li et al, , 2016 are expressed by this parasite stage, thus providing a possible explanation for the effect of PIs on the transformation of ookinetes into oocysts. Moreover, PM VI, whose role is yet undefined, seems crucial for the early oocyst stages of sporogonic development (Li et al, 2016).…”