TREP

TREP (PF3D7_1442600) is a TRAP-family transmembrane protein of Plasmodium sporozoites that couples surface adhesion to the actin-myosin motor to drive gliding motility and tissue traversal during transmission in the mosquito (PMID:19000911, PMID:18441124). It possesses a large extracellular region containing a single thrombospondin type 1 repeat (TSR) domain and a short cytoplasmic tail that binds aldolase, linking it to the glideosome; this tail is functionally interchangeable with that of TRAP (PMID:19000911, PMID:18441124). In P. berghei, TREP is expressed predominantly in oocyst-stage sporozoites, distinguishing it from TRAP, which acts in salivary gland sporozoites, and its disruption severely impairs gliding motility, salivary gland invasion, cell traversal, and in vivo infectivity while leaving in vitro hepatocyte invasion intact — placing TREP specifically in the adhesion, force-transduction, and traversal steps rather than the final invasion step (PMID:19000911, PMID:18346224). TREP contributes to substrate adhesion and to the traction forces sporozoites generate on both dorsal and ventral surfaces, so its loss reduces sporozoite speed, force generation, and environmental guidance during migration (PMID:20159960, PMID:21698220, PMID:40716091). As a TSR-bearing protein, TREP requires O-fucosylation by the protein O-fucosyltransferase POFUT2 for correct trafficking and stability (PMID:28916755).

1. 2008 High

   It was unknown how TREP couples to the parasite invasion machinery; showing that its cytoplasmic tail binds aldolase and can substitute for the TRAP tail established that TREP links surface adhesion to the actin-myosin motor like other TRAP-family invasins.

   Evidence In vitro aldolase pulldown plus genetic complementation of TRAP by the TREP tail in P. berghei

   PMID:18441124

   Open questions at the time

   • Does not identify the extracellular ligand engaged by the TSR domain
   • Does not resolve how tail-motor coupling is regulated during motility
2. 2008 High

   The role of the traversal/adhesion step versus final invasion was unresolved; TREP disruption impaired cell traversal and in vivo infectivity but not in vitro hepatocyte invasion, isolating TREP function to tissue traversal rather than invasion.

   Evidence Targeted gene disruption with cell traversal, in vivo infectivity, and hepatocyte invasion assays in P. berghei

   PMID:18346224

   Open questions at the time

   • Molecular basis of the traversal defect not defined
   • Does not explain why invasion is spared
3. 2008 High

   TREP's stage of action and requirement for motility were unknown; knockout established it as necessary for gliding motility and salivary gland invasion, and qRT-PCR placed its expression in oocyst-stage sporozoites, distinguishing it from TRAP.

   Evidence Targeted knockout with gliding and salivary gland invasion assays plus stage-specific qRT-PCR in P. berghei (and P. falciparum expression)

   PMID:19000911

   Open questions at the time

   • Transcript-level expression not corroborated at protein level in this study
   • Functional division of labor with TRAP not mechanistically dissected
4. 2010 Medium

   Whether TREP acts before or during motility was unclear; live imaging showed tlp- sporozoites adhere poorly under static conditions, establishing that TREP organizes efficient adhesion in concert with TRAP and S6 prior to motility initiation.

   Evidence TIRF microscopy and static/flow adhesion assays with tlp- P. berghei sporozoites

   PMID:20159960

   Open questions at the time

   • Does not resolve the adhesive ligand or receptor engaged
   • Relative contributions of TREP, TRAP, and S6 not quantified
5. 2011 Medium

   It was unknown whether TREP influences directional migration in tissue; imaging in obstacle arrays and skin showed tlp- sporozoites have reduced speed and force and lose the persistence-dispersal correlation, indicating TREP contributes to environmental guidance of migration.

   Evidence In vivo imaging of tlp- versus wild-type sporozoite trajectories in micro-fabricated arrays and skin

   PMID:21698220

   Open questions at the time

   • Mechanism linking adhesion to trajectory guidance not defined
   • Force reduction not directly measured biophysically here
6. 2012 Medium

   Direct evidence for TREP in traversal (versus mere motility loss) was needed; knockout sporozoites failed to traverse MDCK monolayers and were retained in the cytoplasm, confirming a traversal-specific role.

   Evidence MDCK monolayer traversal and dye-retention assays with tlp knockout P. berghei sporozoites

   PMID:22306356

   Open questions at the time

   • Does not identify the molecular effector of cell exit
   • Single traversal system
7. 2016 Medium

   How TREP achieves stability and surface trafficking was unknown; loss of POFUT2 destabilized and mistrafficked TSR-bearing proteins including TREP, establishing O-fucosylation as a post-translational requirement for TREP maturation.

   Evidence Genetic disruption of POFUT2 with protein stability/trafficking and life-cycle phenotyping in P. falciparum and P. berghei

   PMID:28916755

   Open questions at the time

   • TREP is one of several affected TSR proteins, so TREP-specific effect is partly inferred
   • Fucosylation site on TREP not mapped in this study
8. 2025 Medium

   Whether TREP contributes to physical force generation was untested; biophysical measurement showed tlp- sporozoites generate lower traction forces on both surfaces, placing TREP within the force-generating machinery of gliding motility.

   Evidence Traction force microscopy and laser tweezers on tlp- P. berghei sporozoites

   PMID:40716091

   Open questions at the time

   • Does not resolve how TREP surface engagement is transduced into traction
   • Single lab, single study

• The extracellular ligand(s) bound by the TREP TSR domain and the molecular basis distinguishing its traversal role from invasion remain undefined.
• No host or substrate receptor identified for the TSR domain
• No structural model of TREP
• Functional relationship with TRAP and S6 not mechanistically resolved