ICMAP3

ICMAP3 is an intraconoidal microtubule-associated protein of Toxoplasma gondii that couples cytoskeletal organization at the apical complex to the secretory machinery required for host cell invasion. It functions through two distinct isoforms with separable roles: one contributes to the control of intraconoidal microtubule (ICMT) length, while the other mediates docking of two rhoptries at the apical vesicle, as revealed by conditional depletion causing loss of both functions (PMID:38191574). Beyond this depletion-based characterization (PMID:38191574), no further mechanistic detail — including binding partners, structural basis of isoform specialization, or the molecular mechanism of rhoptry docking — has been characterized in the available corpus.

1. 2024 Medium

   It was unknown how intraconoidal microtubule length and rhoptry positioning at the apical vesicle are coordinated; depletion of ICMAP3 established that a single microtubule-associated protein, via two isoforms, governs both ICMT length control and rhoptry docking.

   Evidence Conditional protein depletion with ultrastructural and functional readouts of ICMT length and rhoptry docking at the apical vesicle in Toxoplasma gondii

   PMID:38191574

   Open questions at the time

   • The molecular basis by which the two isoforms partition between ICMT length control and rhoptry docking is not defined
   • No binding partners or structural interactions with microtubules or rhoptries are identified
   • The mechanism linking rhoptry docking to sustained discharge and invasion is not directly demonstrated

• How ICMAP3 isoforms physically associate with intraconoidal microtubules and the apical vesicle, and what partners mediate rhoptry docking, remain unresolved.
• No interactome or reciprocal binding data
• No structural model of ICMAP3 or its isoforms
• Strain-level generality not addressed