Phosphorylation of myosin A regulates gliding motility and is essential for Plasmodium transmission

Abstract

Malaria-causing parasites rely on an actin-myosin-based motor for the invasion of different host cells and tissue traversal in mosquitoes and vertebrates. The unusual myosin A of Plasmodium spp. has a unique N-terminal extension, which is important for red blood cell invasion by P. falciparum merozoites in vitro and harbors a phosphorylation site at serine 19. Here, using the rodentinfecting P. berghei we show that phosphorylation of serine 19 increases ookinete but not sporozoite motility and is essential for efficient transmission of Plasmodium by mosquitoes as S19A mutants show defects in mosquito salivary gland entry. S19A along with E6R mutations slow ookinetes and salivary gland sporozoites in both 2D and 3D environments. In contrast to data from purified proteins, both E6R and S19D mutations lower force generation by sporozoites. Our data show that the phosphorylation cycle of S19 influences parasite migration and force generation and is critical for optimal migration of parasites during transmission from and to the mosquito.

Divergent Plasmodium actin residues are essential for filament localization, mosquito salivary gland invasion and malaria transmission

“…Intriguingly, changes in actin localization resulted in the same effect: less colonization of salivary glands. These observations add further evidence to the hypothesis that the salivary gland represents the most formidable barrier for the parasite to complete its life cycle [49][50][51][52]. We had previously hypothesized that smooth continuous motility is a requirement for efficient invasion of salivary glands.…”

“…Divergent actin residues in localization, invasion and transmission allow penetration. Indeed, studies with Plasmodium myosin A mutants have found that affecting the power stroke has pronounced effects on invasion at different stages of the life cycle [52,55]. Methods are available to investigate force transmission in sporozoites, such as optical tweezers and traction force microscopy, which have carefully delineated force dynamics in Plasmodium [25,43,56].…”

A small-molecule myosin inhibitor as a targeted multi-stage antimalarial

“…A highly desirable feature of antimalarials is activity against multiple stages of the parasite life cycle. Given the importance of the glideosome in sporozoite motility [14], we tested whether PfMyoA inhibition would affect the ability of the parasites to invade and multiply in liver cells, the first intracellular niche occupied by the parasite in a human host. When P. falciparum parasites were preincubated with KNX-115 before adding them to primary human hepatocytes, inhibition of parasite multiplication in the hepatocyte culture was observed with an EC 50 of 182 nM ± 64 nM (n = 2, see Figure 2B for a representative experiment), essentially the same level of inhibition as was seen in the asexual blood stage assay.…”

“…These studies revealed that motor function can be modulated by phosphorylation to optimize force and velocity parameters for the motile and invasion functions of the parasite during its human and mosquito life cycles [12]. The high-resolution structure of PfMyoA combined with biochemical and parasitological studies [14,15] has led to a detailed understanding of how this molecular motor works [12,[18][19][20].…”

“…While all three of these myosins are potentially excellent targets for drug development, Plasmodium falciparum MyoA (PfMyoA), which belongs to the apicomplexan-specific class XIV family of myosins, was of primary interest for us to pursue as a first target because of its essential role in host cell invasion [12,13]. This single-headed myosin motor powers the motility of the sporozoite, merozoite and ookinete stages of the parasite [12][13][14][15] through its ATP-dependent cyclical interactions with actin in the glideosome, a macromolecular complex necessary for the parasite's motility and host cell invasion [16]. It is also biochemically well-characterized by in vitro studies using recombinantly expressed full-length Pf MyoA [17].…”