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Force and retrograde flow in Plasmodium berghei sporozoites

Quadt, Katharina Anna

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Abstract

Plasmodium sporozoites, the motile forms that are transmitted from the mosquito to the mammalian host, use a unique type of locomotion called gliding motility. This motility is powered by an actin-myosin motor underneath the plasma membrane: Myosin pulls on actin-filaments that are connected to adhesins of the thrombospondin-related anonymous protein (TRAP) family including TLP (TRAP-like protein). These membrane-spanning proteins interact with host cell receptors thereby transmitting the generated force to the substrate resulting in a forward movement of the cell. As a consequence, the filamentous actin-adhesin complexes are driven back to the rear of the cell, which is known as retrograde flow. The role of TLP and actin filaments in force production and retrograde flow of Plasmodium berghei sporozoites was investigated using reverse genetics, live cell imaging and optical tweezers. This instrument allows manipulation of microscopic objects by exerting forces in the piconewton range via a highly focused laser beam. In our experiments, we positioned polystyrene particles onto the gliding sporozoites, which actively translocated these beads towards the posterior end of the cell. We found that transport speeds were significantly higher than the sporozoite forward movement (1-2 μm/s) independent of particle size or functionalization. This bead transport most likely indirectly reflects retrograde flow in sporozoites. Wild type sporozoites and transgenic sporozoites lacking the surface protein TLP with and without different concentrations of actin-modulating drugs (cytochalasin D and jasplakinolide) were challenged to pull beads from the optical traps at different forces. These experiments revealed a role of TLP in controlling the retrograde flow by converting it into optimal force transmission for gliding motility. Further, force experiments on mutant sporozoites with altered TLP C-termini refined our hypothesis and suggested a function for the extracellular domain in recruiting surrounding surface proteins and possibly stabilizing them laterally for force transmission. In a second project, I assessed parasite-induced surface protrusions called knobs on P. falciparum-infected erythrocytes using Atomic Force Microscopy (AFM). This analysis revealed that the knobs on infected erythrocytes carrying heterozygous sickle cell- traits were larger but fewer.

Item Type: Dissertation
Supervisor: Schwarz, Prof. Dr. Ulrich
Place of Publication: Heidelberg
Date of thesis defense: 19 March 2018
Date Deposited: 02 May 2018 13:38
Date: 2018
Faculties / Institutes: The Faculty of Bio Sciences > Dean's Office of the Faculty of Bio Sciences
Subjects: 500 Natural sciences and mathematics
570 Life sciences
Controlled Keywords: Plasmodium, Malaria, Force
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