An apical ring protein essential for conoid complex assembly and daughter cell formation in Toxoplasma gondii

Wei Li (), Oliwia Koczy, Peipei Qin, Ignasi Forné, Simon Gras, Jennifer Grünert, Andreas Klingl, Simone Mattei, Elena Jimenez-Ruiz () and Markus Meissner ()
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Wei Li: Sichuan Agricultural University, Department of Parasitology, College of Veterinary Medicine
Oliwia Koczy: Molecular Systems Biology Unit, European Molecular Biology Laboratory (EMBL)
Peipei Qin: Ludwig-Maximilians-University (LMU), Experimental Parasitology, Department of Veterinary Sciences, Faculty of Veterinary Medicine
Ignasi Forné: Ludwig-Maximilians-University (LMU), Protein Analysis Unit, Faculty of Medicine, Biomedical Center (BMC)
Simon Gras: Ludwig-Maximilians-University (LMU), Experimental Parasitology, Department of Veterinary Sciences, Faculty of Veterinary Medicine
Jennifer Grünert: Ludwig-Maximilians-University Munich (LMU), Plant Development, Faculty of Biology
Andreas Klingl: Ludwig-Maximilians-University Munich (LMU), Plant Development, Faculty of Biology
Simone Mattei: Molecular Systems Biology Unit, European Molecular Biology Laboratory (EMBL)
Elena Jimenez-Ruiz: Ludwig-Maximilians-University (LMU), Experimental Parasitology, Department of Veterinary Sciences, Faculty of Veterinary Medicine
Markus Meissner: Ludwig-Maximilians-University (LMU), Experimental Parasitology, Department of Veterinary Sciences, Faculty of Veterinary Medicine

Nature Communications, 2025, vol. 16, issue 1, 1-17

Abstract: Abstract In Toxoplasma gondii, the conoid complex consists of intraconoidal microtubules (ICMTs), preconoidal rings (PCRs), apical polar ring (APR), and the conoid. This organelle plays an important role for initiation of gliding motility, required for host cell invasion and egress. The molecular mechanisms governing stepwise assembly of the conoid complex remain poorly understood. We previously identified CGP, an essential protein required for motility initiation. Here, we demonstrate that CGP is crucial for anchoring FRM1 and other PCR components to mature PCRs, while the initial assembly in daughter cells is unaffected. Cryo-electron tomography of CGP-depleted parasites reveals the absence of the PCRs in the mature parasites, demonstrating that CGP is essential for stabilising the PCRs after replication. Using CGP as bait, we identify a protein required for the early assembly of the nascent conoid complex. The APR scaffold assembly factor (ASAF1) defines the position of the conoid complex before tubulin polymerisation. Depletion of ASAF1 results in failure of conoid complex assembly, disorganised microtubules, and lack of daughter cell formation. Collectively, our findings reveal two essential proteins that play critical roles in the early and late stages of conoid complex formation, providing insight into the mechanisms of conoid complex assembly.

Date: 2025
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DOI: 10.1038/s41467-025-65382-y

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