Actomyosin forces and the energetics of red blood cell invasion by the malaria parasite Plasmodium falciparum

Abstract

All symptoms of malaria disease are associated with the asexual blood stages of development, involving cycles of red blood cell (RBC) invasion and egress by the Plasmodium spp. merozoite. Merozoite invasion is rapid and is actively powered by a parasite actomyosin motor. The current accepted model for actomyosin force generation envisages arrays of parasite myosins, pushing against short actin filaments connected to the external milieu that drive the merozoite forwards into the RBC. In Plasmodium falciparum, the most virulent human malaria species, Myosin A (PfMyoA) is critical for parasite replication. However, the precise function of PfMyoA in invasion, its regulation, the role of other myosins and overall energetics of invasion remain unclear. Here, we developed a conditional mutagenesis strategy combined with live video microscopy to probe PfMyoA function and that of the auxiliary motor PfMyoB in invasion. By imaging conditional mutants with increasing defects in force production, based on disruption to a key PfMyoA phospho-regulation site, the absence of the PfMyoA essential light chain, or complete motor absence, we define three distinct stages of incomplete RBC invasion. These three defects reveal three energetic barriers to successful entry: RBC deformation (pre-entry), mid-invasion initiation, and completion of internalisation, each requiring an active parasite motor. In defining distinct energetic barriers to invasion, these data illuminate the mechanical challenges faced in this remarkable process of protozoan parasitism, highlighting distinct myosin functions and identifying potential targets for preventing malaria pathogenesis.

Live-cell fluorescence imaging of microgametogenesis in the human malaria parasite Plasmodium falciparum

“…Live imaging of microgametogenesis revealed that the erythrocyte membrane likely undergoes echinocytosis in preparation for egress, as evident from the formation of small, spiked projections on the cell surface (Fig 2C). Although echinocytosis is an established feature of asexual blood stage development post-invasion [37], the phenomenon is reported here as a feature of microgametocyte-egress, for the first time. Activated microgametocytes aligned at the periphery of the parasite membrane and eventually ejected from a frequently singular pore that formed in the host erythrocyte (Fig 2C and S3 Video).…”

The multiple functions of actin in apicomplexan parasites

“…Three different components of the glideosome were conditionally knocked out in three independent studiesnamely PfACT1 (Das et al, 2017), PfMyoA (Blake, Haase, & Baum, 2020) and PfGAP45 (Perrin et al, 2018), and in each of these cases, a complete abrogation of invasion was observed. These observations may be explained by the relatively larger size of the nucleus in comparison to the merozoite, differences in shape of the merozoite and tachyzoite, differences in stiffness of the erythrocyte membrane compared to other mammalian cell membranes, or by different requirements of the Plasmodium invasion machinery compared to Toxoplasma.…”

The actomyosin interface contains an evolutionary conserved core and an ancillary interface involved in specificity

“…While the role of PfMyoA in the movement of the parasite had been established 5 , it was only recently shown that PfMyoA is essential for invasion of red blood cells by merozoites, the stage responsible for the symptoms of malaria 3 . PfMyoA thus represents an efficient pharmaceutical target since blocking its activity would impair both the motile and invasive stages of the parasite 6 , 7 .…”