GAPM1A

GAPM1a is an integral membrane protein of the alveoli in Toxoplasma gondii that anchors and stabilizes the cortical microtubule cytoskeleton, thereby maintaining parasite shape, rigidity, and normal cell division (PMID:30674885). Conditional degradation of GAPM1a via the auxin-inducible degron system causes disorganization and subsequent depolymerization of cortical microtubules, rendering parasites shorter and rounder with decreased cellular volume, while extended depletion produces severe division defects (PMID:30674885). Beyond this single conditional-knockdown characterization (PMID:30674885), no further mechanistic detail — including direct binding partners, the molecular basis of microtubule anchoring, or structural information — has been characterized in the available corpus.

1. 2019 Medium

   It was unknown what tethers and stabilizes the cortical microtubule array against the alveolar membrane in Toxoplasma; conditional degradation of GAPM1a showed it is required for cortical microtubule stability and parasite morphology, establishing it as an alveolar membrane anchor for the subpellicular cytoskeleton.

   Evidence Auxin-inducible degron conditional degradation with morphological imaging, microtubule visualization, cell volume measurement, and division assays in Toxoplasma gondii

   PMID:30674885

   Open questions at the time

   • No direct binding partner or interaction interface with microtubules or alveolar components identified
   • The molecular mechanism by which GAPM1a stabilizes versus organizes microtubules is not resolved
   • No structural model of the integral membrane protein
   • Single lab, single strain; not independently replicated

• How GAPM1a physically links the alveolar membrane to cortical microtubules at the molecular level, and what its direct binding partners are, remains unknown.
• No identified direct protein or lipid partners
• No reconstitution of the anchoring activity
• No structural characterization