Affinage · Toxoplasma gondii

PDE1

3'5'-cyclic nucleotide phosphodiesterase domain-containing protein · UniProt S8F656

Annotated
2026-09-07
3 papers in source corpus 3 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TgPDE1 is a cyclic-nucleotide phosphodiesterase that regulates cyclic-nucleotide signaling underlying the motile behaviors of the Toxoplasma gondii tachyzoite (PMID:35107337, PMID:36382189). It is a dual-substrate enzyme that hydrolyzes both cGMP and cAMP, with a kinetic preference for cGMP (Km 18 µM) (PMID:35107337, PMID:36382189), and its catalytic activity is blocked by the PDE inhibitors BIPPO and zaprinast (PMID:36382189). The enzyme distributes across the plasma membrane, inner membrane complex, apical pole, cytosol, dense granules, and rhoptries (PMID:35107337, PMID:36382189), consistent with its role in coordinating the surface and secretory events of the lytic cycle. Functionally, TgPDE1 is required for optimal tachyzoite proliferation, gliding motility, invasion, and egress (PMID:35107337, PMID:36382189), and although it does not physically associate with TgPDE2, the two enzymes are collectively essential and non-redundant, since their combined loss is lethal (PMID:35107337, PMID:36382189). Interactome analysis identified associated kinases and phosphatases that may regulate the enzyme (PMID:35107337, PMID:36382189); the precise regulatory mechanism has not been resolved in the available corpus.

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2020 Medium

    Establishing that TgPDE1 is actually expressed during the disease-relevant tachyzoite stage was the prerequisite for assigning it any role in the lytic cycle.

    Evidence Genomic epitope-tagging and expression detection during the tachyzoite lytic cycle

    PMID:33335684

    Open questions at the time
    • Does not address enzymatic activity, substrate, or function
    • Expression level and stage-specificity not quantified
  2. 2022 High

    Biochemical characterization answered what TgPDE1 does enzymatically, showing it hydrolyzes both cyclic nucleotides but is kinetically tuned to cGMP.

    Evidence In vitro enzyme activity assays and Km determination on protein purified from Toxoplasma lysates

    PMID:35107337 PMID:36382189

    Open questions at the time
    • Relative in vivo flux through cGMP vs cAMP not determined
    • No structural basis for substrate preference
  3. 2022 High

    Loss-of-function phenotyping connected TgPDE1 activity to specific cellular processes, defining it as a regulator of motility, invasion, egress, and proliferation.

    Evidence Knockdown/conditional mutant phenotyping with motility, invasion, egress, and lytic growth assays

    PMID:35107337 PMID:36382189

    Open questions at the time
    • Which cyclic-nucleotide pool drives each phenotype is not resolved
    • Downstream effectors (e.g. PKG/PKA) not directly linked
  4. 2022 High

    Localization studies placed TgPDE1 at the surface and secretory compartments, spatially rationalizing its role in gliding and invasion.

    Evidence Fluorescence microscopy and immuno-electron microscopy in tachyzoites

    PMID:35107337 PMID:36382189

    Open questions at the time
    • Functional significance of each subcellular pool not dissected
    • Membrane-association determinants unknown
  5. 2022 High

    Genetic epistasis established that TgPDE1 and TgPDE2 are collectively essential and non-redundant, defining the essentiality logic of the PDE repertoire.

    Evidence Double-mutant genetic analysis with lethality readout, plus interactome showing no physical PDE-PDE interaction

    PMID:36382189 PMID:35107337

    Open questions at the time
    • Molecular basis of non-redundancy (distinct pools vs distinct substrates) unresolved
    • No reciprocal validation of interactome kinases/phosphatases as functional regulators
  6. 2022 Medium

    Chemogenetic and inhibition assays identified TgPDE1 as a target of BIPPO and zaprinast, providing a pharmacological handle on its activity.

    Evidence Enzyme inhibition assays combined with chemogenetic phenotyping

    PMID:36382189

    Open questions at the time
    • Inhibitor selectivity across TgPDEs not fully defined
    • In vivo consequences of inhibition on parasite viability not quantified

Open questions

Synthesis pass · forward-looking unresolved questions
  • How TgPDE1 activity is regulated by its associated kinases and phosphatases, and how its distinct subcellular pools contribute to motility, invasion, and egress, remains unresolved.
  • No functional validation of identified kinase/phosphatase regulators
  • No structural model of the catalytic or regulatory domains
  • Contribution of individual subcellular pools not separated

Mechanism profile

Synthesis pass · controlled-vocabulary classification
No controlled-vocabulary terms were assigned to this entry.

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2022 TgPDE1 hydrolyzes both cGMP and cAMP (dual-substrate phosphodiesterase activity), as demonstrated by biochemical analysis of TgPDE1 purified from Toxoplasma lysates. Biochemical enzyme activity assay on protein purified from Toxoplasma lysates mSphere High 35107337 36382189
2022 TgPDE1 is preferentially primed to hydrolyze cGMP with a Km of 18 µM, consistent with dual-substrate activity but cGMP preference. In vitro enzyme kinetics (Km determination) Computational and structural biotechnology journal High 36382189
2022 TgPDE1 knockdown causes severe growth defects specifically linked to defects in extracellular motility, establishing TgPDE1 as a regulator of tachyzoite motility. Knockdown screen followed by motility and lytic growth assays mSphere High 35107337 36382189
2022 TgPDE1 localizes to the plasma membrane and cytomembranous compartments in tachyzoites; immuno-electron microscopy further resolved localization to the inner membrane complex, apical pole, plasma membrane, cytosol, dense granules, and rhoptries. Fluorescence localization (plasma membrane/cytomembranous) and immuno-electron microscopy mSphere / Computational and structural biotechnology journal High 35107337 36382189
2022 TgPDE1 interactome studies indicate it does not physically interact with TgPDE2 or other TgPDEs, but may be regulated by kinases and proteases; a retinue of interacting kinases and phosphatases was identified. Interactome/co-immunoprecipitation and mass spectrometry mSphere / Computational and structural biotechnology journal Medium 35107337 36382189
2022 Combined loss of TgPDE1 and TgPDE2 is lethal to the parasite, establishing that these two enzymes are collectively essential for tachyzoite viability and that their functions are non-redundant. Double mutant genetic analysis with lethality readout Computational and structural biotechnology journal High 36382189
2022 TgPDE1 is a target of the PDE inhibitors BIPPO and zaprinast, as demonstrated by enzyme inhibition assays combined with chemogenetic phenotyping. Enzyme inhibition assays and chemogenetic phenotyping Computational and structural biotechnology journal Medium 36382189
2022 TgPDE1 is required for optimal parasite proliferation, gliding motility, invasion, and egress of tachyzoites, as revealed by in vitro phenotyping of TgPDE1 mutants. In vitro phenotyping of conditional mutants (proliferation, motility, invasion, egress assays) Computational and structural biotechnology journal High 35107337 36382189
2020 TgPDE1 is expressed during the tachyzoite lytic cycle in human cells, as confirmed by genomic epitope-tagging. Genomic epitope-tagging and expression detection Computational and structural biotechnology journal Medium 33335684

Source papers

Stage 0 corpus · 3 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2022 Functional Analysis of the Expanded Phosphodiesterase Gene Family in Toxoplasma gondii Tachyzoites. mSphere 19 35107337
2020 The protozoan parasite Toxoplasma gondii encodes a gamut of phosphodiesterases during its lytic cycle in human cells. Computational and structural biotechnology journal 9 33335684
2022 Plasticity and therapeutic potential of cAMP and cGMP-specific phosphodiesterases in Toxoplasma gondii. Computational and structural biotechnology journal 6 36382189