Abstract
The apical complex of Toxoplasma gondii is widely believed to serve essential functions in both invasion of its host cells (including human cells), and in replication of the parasite. The understanding of apical complex function, the basis for its novel structure, and the mechanism for its motility are greatly impeded by lack of knowledge of its molecular composition. We have partially purified the conoid/apical complex, identified ~200 proteins that represent 70% of its cytoskeletal protein components, characterized seven novel proteins, and determined the sequence of recruitment of five of these proteins into the cytoskeleton during cell division. Our results provide new markers for the different subcompartments within the apical complex, and revealed previously unknown cellular compartments, which facilitate our understanding of how the invasion machinery is built. Surprisingly, the extreme apical and extreme basal structures of this highly polarized cell originate in the same location and at the same time very early during parasite replication.
Highlights
Toxoplasma gondii is one of ;5,000 species of obligate intracellular protozoan parasites in the phylum Apicomplexa, many members of which are human or animal pathogens [1]
Isolation of the Conoid/Apical Complex Cytoskeleton Extraction of T. gondii with detergents leaves a ghost consisting of apical complex, attached subpellicular MT [11], and cortical filament network [12] enclosing fragments of other subcellular organelles
After vigorous detergent extraction and sonication, the conoids remain intact, recognizable as bright fluorescent dots when prepared from T. gondii expressing YFP-a-tubulin (Figure 2, red arrows), whereas the subpellicular MT are fragmented and much dimmer (Figure 2, cyan arrows)
Summary
Toxoplasma gondii is one of ;5,000 species of obligate intracellular protozoan parasites in the phylum Apicomplexa, many members of which are human or animal pathogens [1]. Much of the pathogenesis associated with these parasitic diseases is due to tissue damage caused by uncontrolled cycles of hostcell invasion, parasite proliferation, host-cell lysis, and reinvasion. Most Apicomplexan parasites share a set of cytoskeletal structures essential for parasite survival and pathogenesis [2]. Central to both invasion and proliferation is a group of structures at one end of the adult parasite, the apical complex, from which the phylum derives its name. The first sign of daughter formation is the de novo construction of daughter conoids and apical complex, which serve as the focal point for assembly of the complete daughter cytoskeletal and membrane scaffold [2,7]
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