Affinage · Toxoplasma gondii

HIP

HOOK interacting protein HIP · UniProt A0A125YIQ3

Annotated
2026-09-08
3 papers in source corpus 3 papers cited in narrative 5 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

HIP (TGGT1_316650) is a coccidian-specific protein that functions in an apical endosomal trafficking pathway controlling microneme exocytosis in Toxoplasma gondii (PMID:37093045, PMID:37933960). It assembles with TgHOOK and TgFTS into a trimeric complex that partially conserves the eukaryotic FHF (HOOK-FTS-FHIP) endosomal trafficking complex, with HIP serving as the parasite-specific component that replaces FHIP (PMID:37093045, PMID:37933960). The complex localizes in an apically enriched vesicular pattern concentrating at the parasite apical tip (PMID:37093045, PMID:37933960), and is required for the rapid apical trafficking of micronemes as parasites initiate motility (PMID:37933960, PMID:37093045). Conditional depletion of HIP impairs apical positioning and secretion of micronemes and produces severe defects in egress, motility, host cell attachment, and invasion (PMID:37093045). HIP is a CDPK1-dependent phosphorylation substrate, placing it downstream of Ca2+-regulated kinase signaling that governs microneme trafficking (PMID:37933960, PMID:36712004).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2023 High

    It was unknown whether Toxoplasma possesses an FHF-like endosomal trafficking complex; identifying a trimeric HOOK-FTS-HIP assembly established that the parasite adapts this conserved machinery with a lineage-specific subunit.

    Evidence Co-immunoprecipitation, proximity labeling, and conditional depletion with colocalization microscopy in T. gondii

    PMID:37093045 PMID:37933960

    Open questions at the time
    • No structural model of the HOOK-FTS-HIP complex or the HIP-HOOK interface
    • Stoichiometry and assembly order of the trimer not resolved
    • How HIP functionally substitutes for FHIP not defined
  2. 2023 Medium

    The subcellular site of HIP action was undefined; localization to an apically enriched vesicular pattern concentrating at the apical tip, colocalizing with TgHOOK and TgFTS, placed the complex where microneme trafficking occurs.

    Evidence Fluorescence microscopy and colocalization in T. gondii

    PMID:37093045 PMID:37933960

    Open questions at the time
    • Localization determinants not mapped by mutagenesis
    • Whether apical targeting depends on complex assembly not tested
  3. 2023 High

    The functional requirement for HIP was unknown; conditional depletion showed it is needed for apical microneme positioning and secretion, establishing HIP as essential for exocytosis-dependent motility, attachment, invasion, and egress.

    Evidence Conditional knockdown with secretion, motility, invasion, and egress assays in T. gondii

    PMID:37093045

    Open questions at the time
    • Whether microneme secretion defect is a direct trafficking failure or an indirect positioning consequence not separated
    • Contribution of individual complex subunits to each phenotype not dissected
  4. 2023 High

    It was unclear how the trafficking complex is regulated; live imaging linked HOOK-FTS-HIP to rapid apical microneme trafficking at motility onset, connecting endosomal machinery to regulated exocytosis.

    Evidence Live imaging of microneme trafficking with genetic depletion and secretion assays in T. gondii

    PMID:37933960 PMID:37093045

    Open questions at the time
    • The motor or adaptor driving microneme movement along the pathway not identified
    • Kinetic coupling between trafficking and Ca2+ signaling not resolved
  5. 2023 Medium

    How HIP is integrated with Ca2+ signaling was unknown; identification of HIP as a CDPK1-dependent phosphosubstrate placed it downstream of the kinase controlling microneme discharge.

    Evidence Sub-minute phosphoproteomics and bio-orthogonal labeling of CDPK1 substrates in T. gondii strain RH

    PMID:37933960 PMID:36712004

    Open questions at the time
    • Functional consequence of the specific phosphorylation site not validated by mutagenesis
    • Whether phosphorylation regulates complex assembly, localization, or activity unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • How CDPK1 phosphorylation of HIP mechanistically controls microneme trafficking and exocytosis, and the structural basis of the HOOK-FTS-HIP complex, remain open.
  • No phosphomutant analysis linking specific sites to trafficking function
  • No structural characterization of the complex
  • Motor/cargo adaptor connecting the complex to micronemes not identified

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
CDPK1 (KINASE ACTING UPSTREAM OF HIP)TGFTSTGHOOK
Complex memberships
HOOK-FTS-HIP trimeric complex (parasite FHF-like endosomal trafficking complex)

Evidence

Reading pass · 5 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2023 TgHOOK, TgFTS, and HIP (HOOK interacting partner, a coccidian-specific protein) form a trimeric complex in Toxoplasma gondii, partially conserving the eukaryotic FHF (HOOK-FTS-FHIP) endosomal trafficking complex but with parasite-specific components replacing FHIP. Co-immunoprecipitation / complex characterization; conditional depletion; colocalization by fluorescence microscopy mBio High 37093045 37933960
2023 HIP localizes to an apically enriched vesicular pattern and concentrates at the parasite apical tip, where it colocalizes with TgHOOK and TgFTS. Fluorescence microscopy / colocalization mBio Medium 37093045 37933960
2023 Conditional depletion of TgHIP impairs apical positioning and secretion of micronemes and leads to severe defects in egress, motility, host cell attachment, and invasion, demonstrating HIP is required for microneme exocytosis. Conditional knockdown (auxin-inducible degron or equivalent) with secretion assays, motility assays, invasion assays, and egress assays mBio High 37093045
2023 HIP (TGGT1_316650) is identified as a CDPK1-dependent phosphorylation substrate, placing it downstream of Ca2+-regulated kinase signaling that controls microneme trafficking. Sub-minute resolution phosphoproteomics and bio-orthogonal labeling of CDPK1 substrates eLife Medium 36712004 37933960
2023 The HOOK-FTS-HIP complex (partially conserved FHF complex) is required for rapid apical trafficking of micronemes as parasites initiate motility, linking endosomal trafficking machinery to microneme exocytosis. Live imaging of microneme trafficking; genetic knockouts/knockdowns of complex components; secretion assays eLife High 37093045 37933960

Source papers

Stage 0 corpus · 3 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2023 Analysis of CDPK1 targets identifies a trafficking adaptor complex that regulates microneme exocytosis in Toxoplasma. eLife 13 37933960
2023 Toxoplasma gondii HOOK-FTS-HIP Complex is Critical for Secretory Organelle Discharge during Motility, Invasion, and Egress. mBio 6 37093045
2023 Analysis of CDPK1 targets identifies a trafficking adaptor complex that regulates microneme exocytosis in Toxoplasma. bioRxiv : the preprint server for biology 4 36712004