GAP40

GAP40 (PF3D7_0515700) is an essential, polytopic (multi-transmembrane) inner membrane complex (IMC) protein and a core component of the glideosome, the actin-myosin motor that links extracellular adhesins to the IMC to power host-cell entry (PMID:20951968, PMID:28893907). Within this complex GAP40 physically associates with PfGAP45 and PfGAP50, and its loss reduces the levels of both partners in schizonts, indicating that GAP40 stabilizes the assembly or steady-state expression of these glideosome components (PMID:37249423). Functionally, conditional knockdown of GAP40 impairs asexual blood-stage replication by blocking efficient merozoite invasion of red blood cells, while leaving egress and initial attachment intact, defining a specific role in the invasion step (PMID:37249423). GAP40 function is regulated by phosphorylation: alanine substitution of multiple C-terminal serine residues (S370, S372, S376, S405, S409, S420, S445) reduces invasion efficiency, establishing these phosphosites as required for full activity (PMID:37249423). Beyond the asexual stage, GAP40 knockdown impairs gametocyte maturation, extending its role into the sexual stage (PMID:37249423). The kinase(s) writing these phosphorylation marks and the structural basis of GAP40's role in the complex have not been characterized in the available corpus.

1. 2005 Low

   Established GAP40 as part of the conserved actin-myosin motor complex of the P. falciparum merozoite, placing it within the machinery that couples adhesins to the IMC for erythrocyte invasion.

   Evidence Protein identification and immunolocalization in merozoites with comparative genomic analysis across Apicomplexa

   PMID:16321976

   Open questions at the time

   • No direct loss-of-function experiment performed for GAP40 itself; functional role inferred indirectly
   • GAP40's own topology and specific molecular role in the complex not defined here
2. 2010 Medium

   Defined GAP40 as a polytopic IMC membrane protein and an additional glideosome component, giving a physical/topological basis for its position in the motor complex.

   Evidence Molecular characterization, subcellular fractionation, and localization in Toxoplasma with comparative identification of the P. falciparum ortholog

   PMID:20951968

   Open questions at the time

   • Primary functional experiments were performed in Toxoplasma; P. falciparum only noted as ortholog
   • No functional consequence of GAP40 loss tested
3. 2017 Medium

   Confirmed GAP40 as a co-purifying member of the glideosome present at the parasite periphery across multiple invasive stages, extending its association beyond blood-stage merozoites.

   Evidence Co-immunoprecipitation/mass spectrometry of glideosome composition and immunofluorescence across the P. berghei life cycle

   PMID:28893907

   Open questions at the time

   • Shown in P. berghei; direct functional requirement not tested here
   • Nature of GAP40's interactions with individual motor subunits not resolved
4. 2023 High

   Demonstrated that GAP40 is specifically required for efficient merozoite invasion, dissociating its role from egress and attachment and establishing it as essential for blood-stage replication.

   Evidence Conditional TetR-DOZI knockdown with invasion, egress, and attachment assays in P. falciparum

   PMID:37249423

   Open questions at the time

   • Molecular step of invasion that fails upon GAP40 loss not pinpointed
   • Single-lab study
5. 2023 Medium

   Showed that GAP40 stabilizes glideosome partners PfGAP45 and PfGAP50, providing a mechanism by which its loss disrupts motor function.

   Evidence Co-immunoprecipitation and Western blot of partner levels after conditional knockdown in P. falciparum

   PMID:37249423

   Open questions at the time

   • Whether stabilization is at the level of assembly, folding, or turnover not distinguished
   • Reciprocal dependence (whether partners stabilize GAP40) not tested
6. 2023 Medium

   Established that phosphorylation of specific C-terminal serine residues is required for full GAP40 invasion function, identifying a regulatory layer on the protein.

   Evidence Site-directed alanine mutagenesis of phosphoserines S370/S372/S376/S405/S409/S420/S445 with invasion efficiency assays in P. falciparum

   PMID:37249423

   Open questions at the time

   • The kinase(s) writing these phosphomarks not identified
   • How phosphorylation affects complex assembly or motor activity not defined
7. 2023 Medium

   Extended GAP40's role beyond asexual invasion by showing its knockdown impairs gametocyte maturation, implicating it in the sexual stage.

   Evidence Conditional knockdown with gametocyte development/maturation assay in P. falciparum

   PMID:37249423

   Open questions at the time

   • The gametocyte-stage function of GAP40 (whether motor-related or structural) not defined
   • Single-lab study

• The identity of the kinase(s) that phosphorylate GAP40 and the structural basis for how GAP40 organizes and stabilizes the glideosome remain unknown.
• No kinase writer identified for the C-terminal phosphosites
• No structural model of GAP40 within the glideosome
• Mechanism linking GAP40 loss to invasion failure not resolved at molecular resolution