Positioning of large organelles by a membrane- associated cytoskeleton inPlasmodiumsporozoites

Abstract

SummaryCellular organelles are usually linked to the cytoskeleton, which often provides a scaffold for organelle function. In malaria parasites, no link between the cytoskeleton and the major organelles is known. Here we show that during fast, stopand-go motion of Plasmodium sporozoites, all organelles stay largely fixed in respect to the moving parasite. Cryogenic electron tomography reveals that the nucleus, mitochondrion, apicoplast and the microtubules of Plasmodium sporozoites are linked to the parasite pellicle via long tethering proteins. These tethers originate from the inner membrane complex and are arranged in a periodic fashion following a 32 nm repeat. The tethers pass through a subpellicular structure that encompasses the entire parasite, probably as a network of membrane-associated filaments. While the spatial organization of the large parasite organelles appears dependent on their linkage to the cortex, the specialized secretory vesicles are mostly not linked to microtubules or other cellular structures that could provide support for movement.

SPM1 Stabilizes Subpellicular Microtubules in Toxoplasma gondii

“…The close association of subpellicular microtubules with the cytosolic face of the parasite pellicle is clearly mediated by MAPs (21,60,67). Proteins that bridge the region between the microtubules and the overlying membrane are visible by electron microscopy (13,47,60) but have not been identified prior to this report. We describe two novel proteins that colocalize with the Toxoplasma subpellicular microtubules in tachyzoitestage parasites.…”

“…The IMP array is held in place by a lattice of intermediate-filament-like proteins associated with the IMC (3,29,55,56). The subpellicular microtubules are closely associated with the cytosolic face of the IMC, and these microtubules demonstrate a periodicity which suggests that they directly associate with the IMC lattice (47,60). The periodic association of unidentified proteins along subpellicular microtubules is evident both in thin sections and in negatively stained images or frozenhydrated images of isolated microtubules (12,60).…”

Origin, composition, organization and function of the inner membrane complex of Plasmodium falciparum gametocytes

“…Cryo-electron tomography allows 3D visualization of specimens after plunge-freezing in cryogenic liquids to preserve membrane structures (Cyrklaff et al, 2007;Kudryashev et al, 2010). Tomographic analysis of a stage IV gametocyte permits visualization of virtual sections near the surface of the cell without the need for physical sectioning.…”

“…mTRAP is embedded in the parasite plasma membrane and binds to receptors on the host cell, thereby providing the force that drives invasion (Baum et al, 2006a). Underlying the IMC is a microtubule scaffold that forms a major structural element of the invasive stages of apicomplexan parasites (Kudryashev et al, 2010;Sinden, 1982).…”

Microstructured Blood Vessel Surrogates Reveal Structural Tropism of Motile Malaria Parasites

“…[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…”