IMC1c

PF3D7_1003600 (IMC1c) is an alveolin-family protein of the Plasmodium inner membrane complex (IMC) that contributes to the mechanical integrity of the parasite pellicle and is essential for asexual blood-stage development (PMID:25185663, PMID:37712738). In P. berghei, IMC1c is expressed across the merozoite, ookinete, and sporozoite zoite stages and, distinctively among alveolins, is incorporated into the subpellicular network only after pellicle formation rather than concurrently with it (PMID:25185663). IMC1c is S-palmitoylated on a conserved cysteine motif; while palmitoylation is dispensable for its expression, stability, and trafficking, palmitoylation-deficient parasites show reduced osmotic-stress resistance and tensile strength, indicating that lipid anchoring of IMC1c strengthens the connection between the subpellicular network and the IMC membrane (PMID:28223095). IMC1c physically interacts with the alveolin IMC1g via a core sub-repeat motif in IMC1g, an interaction placed in the context of the PHIL1 complex that anchors the glideosome to the subpellicular network (PMID:39576115). However, IMC1c and IMC1g are not interdependent for IMC recruitment in P. falciparum, and unique signatures within the IMC1c alveolin domain—non-interchangeable with those of other alveolins—direct its specialized localization (PMID:41019501).

1. 2014 Medium

   Establishing when and where IMC1c assembles into the pellicle showed it joins the subpellicular network late and is required for parasite viability, distinguishing it from co-assembling alveolins.

   Evidence GFP tagging, live fluorescence microscopy, and repeated failed gene disruption by double-crossover homologous recombination in P. berghei

   PMID:25185663

   Open questions at the time

   • Essentiality inferred from failure to disrupt rather than a conditional depletion
   • Mechanism of late SPN incorporation not defined
   • No molecular partners identified at this stage
2. 2017 Medium

   Testing the functional role of a post-translational modification revealed that S-palmitoylation of IMC1c strengthens cytoskeletal mechanics rather than governing its expression or trafficking.

   Evidence Site-directed mutagenesis of palmitoylation sites with osmotic-stress and mechanical-strength assays in P. berghei

   PMID:28223095

   Open questions at the time

   • Palmitoyl-transferase responsible not identified
   • Direct evidence of lipid anchoring to the IMC membrane not shown biochemically
   • Whether palmitoylation is regulated across stages unknown
3. 2023 Medium

   Confirming essentiality in the human-infective species established IMC1c as required for intraerythrocytic survival of P. falciparum, extending the P. berghei genetic inference.

   Evidence Conditional knockdown / gene essentiality assay in P. falciparum asexual blood stage

   PMID:37712738

   Open questions at the time

   • Terminal phenotype of depleted parasites not detailed in the corpus
   • Which developmental step fails upon loss not resolved
   • Single method reported
4. 2024 Low

   Identifying a direct binding partner placed IMC1c within a defined molecular interaction, linking it to IMC1g and, in that context, to glideosome anchoring via the PHIL1 complex.

   Evidence Pairwise yeast two-hybrid assays with motif mutagenesis identifying the required EKI(V)V(I)EVP sub-repeat in PbIMC1g (P. berghei)

   PMID:39576115

   Open questions at the time

   • Yeast two-hybrid only, with no orthogonal confirmation in the parasite
   • Whether the interaction is direct in vivo unconfirmed
   • IMC1c's specific contribution to the PHIL1 complex not separated from IMC1g's
5. 2025 Medium

   Testing whether the IMC1c–IMC1g interaction governs localization showed the two alveolins are recruited independently, and that IMC1c carries unique, non-interchangeable alveolin-domain signatures for its targeting.

   Evidence Conditional depletion of individual alveolins with fluorescence localization readout and domain-swap experiments in P. falciparum

   PMID:41019501

   Open questions at the time

   • The specific sequence determinants within the alveolin domain that direct localization not mapped
   • The trans factor that recruits IMC1c to the IMC unidentified
   • Reconciliation of independent recruitment with the reported IMC1g interaction not fully resolved

• How IMC1c is recruited to the subpellicular network after pellicle formation, and the molecular basis by which its unique alveolin-domain signatures specify localization, remain open.
• No recruitment factor or targeting mechanism identified
• Structural basis of alveolin-domain specialization unknown
• Direct in-parasite validation of the IMC1g interaction lacking