IMC44

IMC44 is a daughter-specific inner membrane complex (IMC) protein in Toxoplasma gondii that is recruited to nascent daughter buds during endodyogeny as part of a foundational bud assembly complex (PMID:37782662). It is incorporated into the daughter IMC together with IMC43 and IMC32, and its proper stage-specific localization depends on IMC43: depletion of IMC43 causes IMC44 to mislocalize (PMID:37782662). IMC44 physically binds the C-terminal domain of IMC43, which is sufficient for this interaction, indicating that IMC43 directly coordinates IMC44 recruitment during bud formation (PMID:37782662). Beyond its role as a component of this IMC43-IMC32-IMC44 assembly complex, no further biochemical activity or independent function of IMC44 has been characterized in the available corpus.

1. 2023 Medium

   Establishing that IMC44 is a bona fide daughter IMC protein whose recruitment is not autonomous answered whether it is an independent structural element or a downstream client of an organizing factor.

   Evidence Auxin-inducible degron depletion of IMC43 with localization assays of IMC44 in Toxoplasma gondii

   PMID:37782662

   Open questions at the time

   • Whether IMC44 has any function or stability independent of IMC43 is not resolved
   • The consequence of IMC44 loss itself (its own depletion phenotype) is not established
   • The stage of endodyogeny at which IMC44 acts is only partially defined
2. 2023 Medium

   Mapping a direct IMC44-IMC43 interaction to the IMC43 C-terminal domain answered how IMC44 is coordinated, showing the recruitment reflects a specific physical binding rather than mere co-localization.

   Evidence Pairwise yeast two-hybrid assays plus TurboID proximity labelling in Toxoplasma gondii

   PMID:37782662

   Open questions at the time

   • The IMC44 residues/domain that contact IMC43 are not mapped
   • No structural model of the interaction
   • Whether the interaction is direct or bridged is not fully excluded (Y2H is heterologous)
3. 2023 Medium

   Placing IMC44 within an IMC43-IMC32-IMC44 bud assembly complex answered where in daughter IMC biogenesis it acts, defining it as part of the foundational scaffold laid down early in bud formation.

   Evidence TurboID proximity labelling, yeast two-hybrid, and AID depletion with localization and morphology readouts in Toxoplasma gondii

   PMID:37782662

   Open questions at the time

   • The specific molecular contribution of IMC44 to scaffold assembly versus IMC32/IMC43 is not distinguished
   • The order of recruitment within the complex is not resolved
   • No cross-strain or in vivo confirmation of the complex

• The intrinsic molecular activity of IMC44 and its own loss-of-function phenotype remain unknown.
• No IMC44-specific depletion phenotype reported
• No biochemical or enzymatic activity assigned to IMC44
• No structural or interface-level characterization of its binding to IMC43