GAPM3

GAPM3 (PF3D7_1406800) is a polytopic membrane protein of the Plasmodium falciparum inner membrane complex (IMC) that functions as a structural component linking the glideosome motor to the subpellicular cytoskeleton (PMID:19561073). At the IMC it forms highly SDS-resistant oligomeric assemblies and co-purifies with both cytoskeletal alveolin proteins and the actin-myosin motor, consistent with a tethering role (PMID:19561073), and this motor association is corroborated by its recovery in MyoA-GFP glideosome pulldowns from schizonts (PMID:28893907). On merozoites, GAPM3 co-localizes and assembles into a heteromeric complex with two related six-transmembrane GAPM-family proteins (PMID:19465059). GAPM3 is palmitoylated in asexual stages, a modification consistent with its membrane residence (PMID:22901544). Its proper IMC localization and stability depend on an intact PHIL1-complex environment: GAPM3 was detected among PhIL1-GFP interactors in gametocytes (PMID:28985225), and in P. berghei depletion of the PHIL1-complex protein IMC1g mislocalized and destabilized GAPM3 (PMID:39576115). Beyond this structural/anchoring role, no catalytic activity or direct loss-of-function phenotype for GAPM3 itself has been characterized in the available corpus.

1. 2009 Medium

   Establishing where GAPM3 acts and what it binds was the first question; localizing it to the IMC and showing co-purification with alveolins and the motor defined it as a candidate structural bridge between the glideosome and the cytoskeleton.

   Evidence Immunofluorescence, SDS-resistant oligomer analysis, and co-purification with alveolins and actin-myosin motor components in P. falciparum

   PMID:19561073

   Open questions at the time

   • Co-purification does not establish direct binding partners
   • No loss-of-function test of the proposed tethering role
   • Stoichiometry and architecture of the oligomers undefined
2. 2009 Medium

   Whether GAPM3 acts alone or within a family assembly was addressed by showing it forms a heteromeric complex with two related six-transmembrane proteins on merozoites.

   Evidence Immunofluorescence colocalization and immunoprecipitation with specific antibodies in P. falciparum merozoites

   PMID:19465059

   Open questions at the time

   • Identities/roles of the two partner proteins not detailed here
   • Functional consequence of the heteromeric assembly untested
   • Complex composition in other life stages unknown
3. 2012 Medium

   How a multipass membrane protein is anchored/regulated was partly answered by identifying GAPM3 as a palmitoylated protein in asexual stages.

   Evidence Acyl-biotin exchange and metabolic click labeling with quantitative mass spectrometry in P. falciparum

   PMID:22901544

   Open questions at the time

   • Palmitoylation sites not mapped
   • Functional role of the modification untested
   • Responsible palmitoyltransferase unknown
4. 2017 Medium

   The earlier partial co-purification with the motor was strengthened by recovering GAPM3 in a MyoA-GFP glideosome pulldown, confirming association with the motor complex.

   Evidence GFP-tagged MyoA co-immunoprecipitation followed by LC-MS/MS in P. falciparum 3D7 schizonts

   PMID:28893907

   Open questions at the time

   • Does not establish direct GAPM3-MyoA contact
   • No demonstration that GAPM3 is required for motor assembly or function
5. 2017 Low

   Linkage of GAPM3 to the PHIL1 structural network was first hinted by its detection among PhIL1 interactors in gametocytes.

   Evidence PhIL1-GFP GFP-Trap immunoprecipitation followed by LC-MS/MS in P. falciparum 3D7 stage IV gametocytes

   PMID:28985225

   Open questions at the time

   • Did not reach the study's significance threshold
   • Single pulldown without reciprocal validation
   • Direct vs indirect association unresolved
6. 2024 Low

   Whether GAPM3 IMC localization depends on the PHIL1 network was addressed by showing that depleting the PHIL1-complex protein IMC1g mislocalizes and destabilizes GAPM3.

   Evidence Conditional knockdown of PbIMC1g with IFA and immunoblotting readouts in P. berghei

   PMID:39576115

   Open questions at the time

   • Indirect evidence from a different gene's knockdown
   • Shown in P. berghei, not P. falciparum
   • Does not distinguish direct dependency from general IMC disruption

• The intrinsic function of GAPM3 itself—whether it is required for glideosome assembly, motility, or invasion—remains unresolved because no direct loss-of-function study of GAPM3 has been reported.
• No GAPM3 knockout/knockdown phenotype
• No structural model of the oligomer or its motor/cytoskeleton contacts
• Molecular activity beyond structural anchoring undefined