Pf112

PTEX150 (PF3D7_1436300) is a core structural component of the Plasmodium translocon of exported proteins (PTEX), the ATP-powered machinery embedded in the parasitophorous vacuole membrane (PVM) that drives export of parasite proteins into the host erythrocyte (PMID:19536257). Within the complex, PTEX150 is positioned between the membrane-associated pore-former EXP2 and the AAA+ ATPase HSP101 in a stable macromolecular assembly of >1230 kDa, and it forms a stable subcomplex with EXP2 that provides the platform for HSP101 docking (PMID:22253438, PMID:35192672). Cryo-EM of the endogenous complex shows PTEX150 and EXP2 interdigitating into a static, funnel-shaped, pseudo-seven-fold channel spanning the vacuolar membrane, with PTEX150 captured in distinct 'engaged' and 'resetting' translocation states as cargo is threaded through by HSP101 (PMID:30150771). Functionally, PTEX150 is essential for blood-stage survival and is required to export all classes of cargo — both PEXEL-motif and PEXEL-negative proteins, including the virulence factor PfEMP1 — across the PVM, but it is distinct from EXP2 in that it does not contribute to the nutrient-permeable channel activity EXP2 performs independently of HSP101 (PMID:25043043, PMID:30150733). Beyond blood stages, PTEX150 is expressed in liver stages and is required there for PEXEL-protein export and full liver-stage fitness (PMID:38968107), and its conditional depletion also perturbs haemoglobin digestion through interactions with the food-vacuole proteases falcipain 2a and plasmepsin II (PMID:37523385).

1. 2009 High

   Before its discovery it was unknown how parasite proteins crossed the parasitophorous vacuole membrane; identifying PTEX150 as a core component of an ATP-powered PVM translocon defined the physical machinery of protein export.

   Evidence Co-immunoprecipitation and biochemical isolation of the PTEX complex from P. falciparum

   PMID:19536257

   Open questions at the time

   • Did not define PTEX150's specific role within the complex versus other subunits
   • No structural or stoichiometric information
2. 2012 High

   The spatial and temporal logic of translocon assembly was unresolved; tracking PTEX150 from merozoite dense granules to the PVM and ordering the subunits established it as a stable scaffold positioned between EXP2 and HSP101.

   Evidence Immunofluorescence, subcellular fractionation, Blue Native PAGE and co-immunoprecipitation in P. falciparum

   PMID:22253438

   Open questions at the time

   • Subunit ordering was biochemically inferred, not resolved structurally
   • Did not establish which subunit forms the conducting pore
3. 2012 Low

   Whether PTEX operated outside blood stages was open; detecting PTEX150 protein in liver-stage schizonts showed the machinery is present during hepatic infection.

   Evidence In vivo infection of liver-chimeric FRG mice with immunofluorescence detection of PTEX150 in P. falciparum liver stages

   PMID:22996664

   Open questions at the time

   • Detection only, no functional test of PTEX150 in liver stages
   • Did not show liver-stage export depends on PTEX150
4. 2013 Medium

   The necessity of PTEX150 for parasite viability was untested; repeated failed deletions in the rodent model provided genetic evidence that it is essential for blood-stage survival.

   Evidence Attempted gene deletion / reverse genetics in P. berghei (two independent studies)

   PMID:23869529 PMID:24076174

   Open questions at the time

   • Failed deletion is negative evidence and does not itself define the essential molecular function
   • Did not distinguish an export role from other possible functions
5. 2014 High

   It remained unknown whether PTEX150 is directly required for cargo export or merely structurally present; conditional knockdown showed that loss blocks translocation of both PEXEL and PEXEL-negative cargo and impairs growth, establishing it as functionally essential for export.

   Evidence Inducible conditional knockdown with export and in vitro/in vivo growth assays in P. falciparum

   PMID:25043043

   Open questions at the time

   • Did not reveal the structural mechanism of translocation
   • Did not distinguish PTEX150's role from EXP2's channel activity
6. 2018 High

   The physical architecture of the conducting channel and PTEX150's place in it were unknown; near-atomic cryo-EM showed PTEX150 interdigitates with EXP2 to build a static funnel-shaped channel and captured it in engaged and resetting translocation states.

   Evidence Cryo-EM of the endogenous complex isolated via CRISPR-Cas9 epitope tags in P. falciparum

   PMID:30150771

   Open questions at the time

   • Static structure does not resolve the full dynamic threading cycle
   • HSP101 power-stroke coupling to PTEX150 not directly visualized
7. 2018 High

   Whether PTEX150 shares EXP2's nutrient-channel function was unclear; combining knockdown with electrophysiology showed PTEX150 is required for protein export but not for the HSP101-independent nutrient-permeable channel, separating the two roles.

   Evidence Regulated knockdown, patch-clamp electrophysiology and mutagenesis in P. falciparum

   PMID:30150733

   Open questions at the time

   • Did not define which PTEX150 residues mediate cargo conduction
   • Mechanism coupling PTEX150 to HSP101 ATP hydrolysis not resolved
8. 2018 Medium

   Whether translocon components redistribute during export was open; trapping cargo showed EXP2-containing loop extensions form at the PVM while PTEX150 stays restricted to defined export zones, indicating it does not follow cargo into these extensions.

   Evidence Conditional DHFR cargo trapping with immunofluorescence colocalization and live imaging in P. falciparum

   PMID:29696751

   Open questions at the time

   • Single-lab localization observation with limited PTEX150-specific follow-up
   • Functional consequence of PTEX150 restriction not tested
9. 2021 Medium

   Direct engagement of PTEX150 with integral-membrane cargo during translocation was unproven; isolating a mini-SURFIN4.1 intermediate complex containing PTEX150 showed it is part of the active cargo-engaged machinery.

   Evidence Co-immunoprecipitation of a cargo-clogged translocation intermediate in P. falciparum

   PMID:33901679

   Open questions at the time

   • Single-lab intermediate capture
   • Did not resolve how integral-membrane cargo is extracted and threaded
10. 2021 Medium

    Whether PTEX150 promoter activity governs liver-stage export competence was tested; restoring HSP101 under the ptex150 promoter failed to rescue early liver-stage PEXEL export, showing PTEX150 promoter activity alone does not determine export competence.

    Evidence Promoter-swap transgenics in P. berghei with immunofluorescence of PEXEL export

    PMID:34956312

    Open questions at the time

    • Indirect readout centered on HSP101, limited direct data on PTEX150 protein
    • Did not identify the determinant of liver-stage export competence
11. 2022 Medium

    How HSP101 is recruited to the translocon was unresolved; identifying a stable EXP2-PTEX150 subcomplex that facilitates HSP101 docking established PTEX150 as a scaffold bridging the pore and the ATPase.

    Evidence Reciprocal co-immunoprecipitation and biochemical fractionation in P. falciparum

    PMID:35192672

    Open questions at the time

    • Docking interface residues not mapped
    • Order of assembly in vivo not fully resolved
12. 2023 Medium

    The functional stoichiometry of the translocon was unknown; ER sequestration of PTEX150 revealed that vacuolar PTEX150, unlike HSP101, is not maintained in excess over export demand, distinguishing subunit spare capacity.

    Evidence knockER inducible ER sequestration with export functional assays in P. falciparum

    PMID:37552754

    Open questions at the time

    • Single novel-tool study
    • Quantitative subunit ratios in the assembled channel not measured
13. 2023 Medium

    A role for PTEX150 beyond export into the host was unexpected; knockdown perturbed haemoglobin digestion and PTEX core components interacted with falcipain 2a and plasmepsin II, implicating PTEX150 in trafficking haemoglobinases to the food vacuole.

    Evidence Conditional knockdown, co-immunoprecipitation with haemoglobinases, transgenic reporters and haemoglobin digestion assays in P. falciparum

    PMID:37523385

    Open questions at the time

    • Whether the effect is direct trafficking or an indirect consequence of export failure not fully resolved
    • Route of protease delivery to the cytostome not defined
14. 2024 High

    The functional requirement for PTEX150 in liver stages was untested; conditional disruption in sporozoites left mosquito and hepatocyte-invasion stages intact but blocked liver-stage PEXEL export and attenuated liver-stage fitness in humanized mice.

    Evidence Conditional FlpL/FRT excision in sporozoites, infection of humanized mice, immunofluorescence of PEXEL proteins in P. falciparum

    PMID:38968107

    Open questions at the time

    • Partial fitness reduction indicates export is not strictly required for all liver-stage growth
    • Cargo dependencies beyond LISP2 and CSP not enumerated

• How PTEX150's conformational cycling is mechanically coupled to HSP101 ATP hydrolysis to power cargo threading, and how it is targeted to defined PVM export zones, remains unresolved.
• No dynamic structural model of the full threading cycle
• Determinants of PTEX150 restriction to export zones unknown
• Interface residues for EXP2 and HSP101 not mapped