CGP

CGP (conoid gliding protein) is an essential conoid protein of Toxoplasma gondii that maintains the structural integrity of the preconoidal rings (PCRs) and is required for the activation of gliding motility during egress (PMID:35538310, PMID:41315181). CGP acts late during egress, and its conditional knockout produces a gliding motility defect (PMID:35538310). CGP stabilises PCRs after replication rather than driving their initial assembly: cryo-electron tomography of CGP-depleted parasites shows loss of PCRs in mature parasites while daughter-cell PCR assembly still occurs, and CGP is required to anchor FRM1 and other PCR components to mature PCRs (PMID:41315181). Using CGP as bait, ASAF1 was identified as an interacting scaffold factor that defines the position of the conoid complex prior to tubulin polymerisation, and whose depletion abolishes conoid complex assembly, disorganises microtubules, and blocks daughter cell formation (PMID:41315181).

1. 2022 Medium

   Establishing that a previously uncharacterised conoid protein controls when parasites become motile, CGP was shown to act late in egress and to be required for activation of gliding motility.

   Evidence Conditional knockout (DiCre) plus splitCas9 phenotypic screen in an F-actin dynamics indicator strain of T. gondii

   PMID:35538310

   Open questions at the time

   • The structural role of CGP at the conoid was not defined
   • Molecular partners of CGP were not identified
   • How the motility defect connects to conoid architecture was unresolved
2. 2025 High

   Resolving where CGP acts structurally, cryo-ET and interactome analysis showed CGP stabilises preconoidal rings after replication and anchors FRM1 and other PCR components to mature PCRs without being needed for initial PCR assembly.

   Evidence Conditional depletion, cryo-electron tomography, and co-immunoprecipitation/proximity labelling with CGP as bait in T. gondii

   PMID:41315181

   Open questions at the time

   • The mechanism by which CGP physically anchors FRM1 to PCRs is not defined
   • How loss of PCR integrity mechanistically causes the gliding defect is not established
3. 2025 Medium

   Extending the CGP interactome, ASAF1 was identified as a CGP-associated scaffold factor that positions the conoid complex before tubulin polymerisation, linking CGP to early conoid/microtubule organisation during daughter cell formation.

   Evidence Affinity purification/co-IP with CGP as bait, conditional depletion of ASAF1, and cryo-electron tomography in T. gondii

   PMID:41315181

   Open questions at the time

   • Direct versus indirect nature of the CGP–ASAF1 interaction is not resolved
   • Whether CGP itself contributes to conoid positioning through ASAF1 is not established
   • The molecular basis of ASAF1 scaffolding activity is uncharacterised

• The biochemical mechanism linking CGP-dependent PCR stabilisation to activation of gliding motility, and the structural basis of its interactions with FRM1 and ASAF1, remain open.
• No structural model of CGP within the PCR
• No mapping of CGP binding interfaces to FRM1 or ASAF1
• Mechanistic coupling of PCR integrity to motility activation not defined