Structural basis for chirality and directional motility ofPlasmodiumsporozoites

Abstract

SummaryPlasmodium sporozoites can move at high speed for several tens of minutes, which is essential for the initial stage of a malaria infection. The crescent-shaped sporozoites move on 2D substrates preferably in the same direction on circular paths giving raise to helical paths in 3D matrices. Here we determined the structural basis that underlies this type of movement. Immature, non-motile sporozoites were found to lack the subpellicular network required for obtaining the crescent parasite shape. In vitro, parasites moving in the favoured direction move faster and more persistent than the few parasites that move in the opposite direction. Photobleaching experiments showed that sporozoites flip their ventral side up when switching the direction of migration. Cryo-electron tomography revealed a polarized arrangement of microtubules and polar rings towards the substrate in Plasmodium sporozoites, but not in the related parasite Toxoplasma gondii. As a consequence, secretory vesicles, which release proteins involved in adhesion, migration and invasion at the front end of the parasite, are delivered towards the substrate. The resulting chiral structure of the parasite appears to determine the unique directionality of movement and could explain how the sporozoite achieves rapid and sustained directional motility in the absence of external stimuli.

Plasmodium berghei Sporozoites Acquire Virulence and Immunogenicity during Mosquito Hemocoel Transit

“…This notion is fully supported by a recent study using automated tracking of large sporozoite populations (11). Another recent study using advanced microscopy revealed that during the process of maturation sporozoites acquire their distinct curvature, which is structured by a subpellicular network of polarized microtubules (12). However, no structural information is available yet for sporozoites in transit in the mosquito hemocoel.…”

Microstructured Blood Vessel Surrogates Reveal Structural Tropism of Motile Malaria Parasites

“…To do so we isolated immature sporozoites from the oocysts residing at the gut wall, which can only weakly adhere and basically do not move on substrates and are mostly thinner and longer then salivary gland sporozoites. [19,32] When placed between pillars, the midgut sporozoites did not migrate (Figure 7). Only few showed a type of motility previously described as patch-gliding, where parasites are attached to the substrate with a single adhesion site and move over this adhesion site back and forth.…”

“…[19] This structure can be visualized with cryo-electron tomography in mature sporozoites isolated from the mosquito salivary glands, while it is absent from immature sporozoites isolated from parasitic cysts of the mosquito gut, where sporozoites form. [19,31] Only mature sporozoites are able to attach efficiently to a flat substrate and perform robust motility. [32,33] Our current dataset suggests that sporozoites have a given curvature that is normally distributed over a certain range and…”

“…[10] Furthermore, Plasmodium sporozoites are curved cells with a curvature that is similar to the curvature of the blood capillaries they enter. [19,20] In vivo experiments analyzing the tracks of many parasites further showed that sporozoites migrate with slightly reduced speed around capillaries compared to their migration in the surrounding tissue. [21] Around blood capillaries they also adapt a more uniform curvature that appears different from the surrounding tissue, where they often change their shape.…”

Cryo-electron tomography reveals four-membrane architecture of the Plasmodium apicoplast

“…Cryo-electron tomography is widely regarded to introduce the fewest artefacts during preparation as the specimen is rapidly frozen (within a few milliseconds) thus preserving molecular details and membrane arrangements [19,20]. This technique has been used successfully to investigate membranous and cytoskeletal structures in sporozoites of P. berghei [15,21-23] and Maurer’s clefts of P. falciparum infected red blood cells [24,25]. Cryo-electron tomography does not include staining with heavy metal salts and thus provides lower contrast, though being sufficient to examine membranes [26].…”