GAP80

GAP80 is a glideosome-associated protein of Toxoplasma gondii that nucleates a distinct basal-pole motor complex, recruiting the class XIV myosin C (MyoC) to the basal polar ring in a spatial arrangement separate from the canonical apical MyoA-glideosome (PMID:25393004). Within this complex, MyoC shares the same myosin light chains as MyoA and engages the integral IMC proteins GAP50 and GAP40, establishing that the two glideosomes are built from overlapping core components differing in their motor and positional determinants (PMID:25393004). Restriction of MyoC to the posterior pole depends on the IMC-associated protein IAP1, which acts as the localization determinant for the GAP80-assembled complex (PMID:25393004). The two glideosomes are functionally plastic: removal of MyoA triggers compensatory relocalization of MyoC along the pellicle and apical cap, sustaining residual host-cell invasion (PMID:25393004). Beyond these findings, no further mechanistic detail on GAP80 has been characterized in the available corpus.

1. 2014 High

   Whether Toxoplasma possesses motor complexes beyond the apical MyoA-glideosome was unresolved; identifying GAP80 as the scaffold of a MyoC-recruiting basal complex established a second, spatially distinct glideosome.

   Evidence genetic deletion and subcellular localization in Toxoplasma gondii

   PMID:25393004

   Open questions at the time

   • structural basis of how GAP80 tethers MyoC to the basal polar ring not defined
   • biochemical activity of GAP80 itself not characterized
   • quantitative contribution of the basal glideosome to motility not measured
2. 2014 Medium

   It was unknown whether the two glideosomes were biochemically independent or shared parts; co-immunoprecipitation showed MyoC uses the same light chains as MyoA and binds GAP50 and GAP40, revealing a shared core architecture.

   Evidence co-immunoprecipitation / protein interaction studies in Toxoplasma gondii

   PMID:25393004

   Open questions at the time

   • stoichiometry and direct versus indirect nature of interactions not resolved
   • no reciprocal validation of the shared light-chain interactions reported
3. 2014 Medium

   What confines MyoC to the posterior pole was unclear; deletion analysis identified IAP1 as the determinant restricting MyoC localization within the GAP80 complex.

   Evidence genetic deletion with localization analysis in Toxoplasma gondii

   PMID:25393004

   Open questions at the time

   • molecular mechanism by which IAP1 restricts localization not defined
   • relationship between IAP1 and GAP80 in complex assembly not established
4. 2014 Medium

   Whether the basal glideosome could substitute for the apical motor was untested; sequential MyoA deletion showed MyoC relocalizes to the pellicle and apical cap and sustains residual invasion, demonstrating functional plasticity.

   Evidence genetic deletion of MyoA with localization and invasion assays in Toxoplasma gondii

   PMID:25393004

   Open questions at the time

   • signal triggering compensatory relocalization unknown
   • efficiency of MyoC-driven invasion relative to MyoA not quantified in detail

• The intrinsic biochemical function of GAP80, its structure, and how it is targeted to the basal polar ring remain unresolved.
• no structural model of GAP80 or the basal glideosome
• no defined enzymatic or binding activity for GAP80 itself
• recruitment mechanism to the basal polar ring uncharacterized