Cytoskeletal Components of an Invasion Machine—The Apical Complex of Toxoplasma gondii

TLDR

The apical complex of *Toxoplasma gondii* is essential for host cell invasion and parasite replication, yet its molecular composition and motility mechanisms remain poorly understood. By partially purifying the conoid/apical complex, the authors identified roughly 200 proteins—about 70 % of its cytoskeletal components—characterized seven novel proteins, and mapped the recruitment sequence of five proteins during cell division. These results provide new subcompartment markers, uncover previously unknown cellular compartments, and show that the extreme apical and basal structures arise from the same site early in replication, advancing understanding of the invasion machinery.

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 approximately 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.