Biology subjects

Sun, S. Y.

Publications and source records attributed to Sun, S. Y..

3 recordsLinked to original sources

bioRxiv2022

Cryogenic electron tomography reveals novel structures in the apical complex of Plasmodium falciparum

Intracellular infectious agents, like the malaria parasite, Plasmodium falciparum, face the daunting challenge of how to invade a host cell. This problem may be even harder when the host cell in question is the enucleated red blood cell. Evolution has provided P. falciparum and related single-celled parasites within the phylum Apicomplexa with a collection of organelles at their apical end that mediate invasion. This apical complex includes at least two sets of secretory organelles, micronemes and rhoptries, and several structural features like apical rings and a putative pore through which proteins may be introduced into the host cell during invasion. In this paper, we perform cryogenic electron tomography (cryo-ET) on isolated merozoites to visualize the apical machinery. Through tomography reconstruction of cellular compartments, we see new details of known structures like the rhoptry tip interacting directly with a rosette resembling the recently described rhoptry-secretory-apparatus (RSA), or with an apical vesicle docked beneath the RSA. Subtomogram averaging reveals that the apical rings have a fixed number of repeating units, each of which is similar in overall size and shape to the units in the apical rings of tachyzoites of Toxoplasma gondii. Comparison of these polar rings in Plasmodium and Toxoplasma parasites also reveals them to have a structurally conserved assembly patterning. These results provide new insight into the essential features of this remarkable machinery used by apicomplexan parasites to invade their respective host cells.

cell biology↗

bioRxiv2022

Ionophore-stimulation promotes re-organization of the invasion machinery of Toxoplasma gondii

Host cell invasion by intracellular, eukaryotic parasites within the phylum Apicomplexa, is a remarkable and active process involving the coordinated action of apical organelles and other structures. To date, capturing how these structures interact during invasion has been difficult to observe in detail. Here, we used cryogenic electron tomography to image the apical complex of Toxoplasma gondii tachyzoites under conditions that mimic resting parasites and those primed to invade through stimulation with calcium ionophore. Through the application of Mixed Scale Dense networks for image-processing, we developed a highly efficient pipeline for annotation of tomograms, enabling us to identify and extract densities of relevant subcellular organelles and accurately analyze features in 3D. The results reveal a dramatic change in the shape of the anteriorly located apical vesicle upon its apparent fusion with a rhoptry, that occurs only in the stimulated parasites. We also present information indicating that this vesicle originates from the vesicles that parallel the intraconoidal microtubules and that the latter two structures are linked by a novel tether. We show that a rosette structure previously proposed to be involved in rhoptry secretion is associated with apical vesicles beyond just the most anterior one. This result, suggesting multiple vesicles are primed to enable rhoptry secretion, may shed light on the mechanisms Toxoplasma employs to enable repeated invasion attempts. Using the same approach, we examine Plasmodium falciparum merozoites and show that they too possess an apical vesicle just beneath a rosette, demonstrating evolutionary conservation of this overall subcellular organization. Significance StatementParasites in the phylum Apicomplexa are responsible for some of the most important parasitic diseases of humans, such as malaria and toxoplasmosis. Invasion by these obligatory, intracellular parasites depends on protein injection into the host cell. Using cryogenic electron tomography, we reveal evolutionarily conserved features shared by the invasive forms of Plasmodium falciparum and Toxoplasma gondii. By comparing resting Toxoplasma tachyzoites with those primed to invade we also gain new insight into the very first steps in invasion. For this work, we take an interdisciplinary approach, adopting a mixed-scale dense neural network that enables efficient and objective processing of the data. Combined, the results provide new information on how these important parasites accomplish the essential step of invasion.

cell biology↗

bioRxiv2021

Cryo-ET reveals two major tubulin-based cytoskeleton structures in Toxoplasma gondii

In the obligate intracellular parasite, Toxoplasma gondii, the subpellicular microtubules (SPMTs) help maintain shape, while the apical conoid (also tubulin-based) is implicated in invasion. Here, we use cryo-electron tomography to determine the molecular structures of the SPMTs and the conoid-fibrils (CFs) in vitrified and detergent-lysed parasites. Subvolume densities from detergent-extracted parasites yielded averaged density maps at subnanometer resolutions, and these were related back to their architecture in situ. An intraluminal spiral (IS) lines the interior of the 13-protofilament SPMTs, revealing a preferred orientation of these microtubules relative to the parasites long axis. Each CF is composed of 9 tubulin protofilaments, that produce a comma-shaped cross-section, plus additional associated components. Conoid protrusion, a crucial step in invasion, is associated with an altered pitch of each CF. The use of basic building blocks of protofilaments and different accessory proteins in one organism, illustrates the versatility of these critical structures.

molecular biology↗