Affinage · Toxoplasma gondii

PHYb

putative hypoxia- inducible factor prolyl hydroxylase (phd2) · UniProt S8EZF0

Annotated
2026-09-08
2 papers in source corpus 2 papers cited in narrative 3 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TgPHYb is a 2-oxoglutarate-dependent prolyl hydroxylase in Toxoplasma gondii that acts as a sensor of elevated oxygen levels, supporting parasite growth, invasion, and protein synthesis specifically at high but not low O2 tensions (PMID:30914506). Its mechanistic role is to sustain translational elongation: PHYb maintains translation elongation factor eEF2 in an active, ribosome-engaged state, and its depletion causes eEF2 hyper-phosphorylation, reduced elongation rates, and lower abundance of parasite adhesins (PMID:30914506). This regulation operates through a stress-response pathway in which PHYb acts upstream of CDPK3, preventing CDPK3-mediated hyper-phosphorylation of eEF2 that would otherwise block eEF2-ribosome interaction and halt elongation (PMID:37272703). Beyond this oxygen-sensing/eEF2-CDPK3 axis, the direct hydroxylation substrate of PHYb has not been characterized in the available corpus.

Mechanistic history

Synthesis pass · year-by-year structured walk · 3 steps
  1. 2019 Medium

    Established that TgPHYb is a functional 2-oxoglutarate-dependent prolyl hydroxylase whose requirement is oxygen-dependent, defining it as an oxygen sensor rather than a constitutive housekeeping enzyme.

    Evidence Conditional knockdown strain assayed for growth, invasion, and protein synthesis under varying oxygen tensions in T. gondii

    PMID:30914506

    Open questions at the time
    • Direct prolyl hydroxylation substrate of PHYb not identified
    • Molecular mechanism of oxygen sensing not resolved
  2. 2019 Medium

    Connected PHYb to the translation machinery by showing it promotes eEF2 activity, linking oxygen sensing to control of translational elongation and adhesin production.

    Evidence Conditional knockdown with eEF2 phosphorylation, elongation-rate, and adhesin-abundance readouts in T. gondii

    PMID:30914506

    Open questions at the time
    • Whether eEF2 or an upstream factor is the direct hydroxylation target unknown
    • Kinase responsible for eEF2 hyper-phosphorylation not yet identified at this stage
  3. 2023 Medium

    Placed PHYb in a defined stress-response pathway upstream of the kinase CDPK3, showing PHYb prevents CDPK3-mediated eEF2 hyper-phosphorylation that otherwise blocks eEF2-ribosome engagement and elongation.

    Evidence Genetic epistasis with CDPK3 loss-of-function in extracellularly stressed parasites, eEF2 phosphorylation assays, and CDPK3-eEF2 co-immunoprecipitation in T. gondii

    PMID:37272703

    Open questions at the time
    • Biochemical link between PHYb hydroxylase activity and CDPK3 suppression not established
    • Direct PHYb substrate connecting oxygen sensing to CDPK3 regulation unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • The direct hydroxylation substrate of PHYb and the biochemical mechanism coupling its enzymatic activity to suppression of CDPK3-mediated eEF2 phosphorylation remain unresolved.
  • No direct prolyl hydroxylation substrate identified
  • No structural model of PHYb
  • Mechanism linking hydroxylase activity to CDPK3 inhibition undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
CDPK3 (CALCIUM-DEPENDENT PROTEIN KINASE, DOWNSTREAM EFFECTOR ON EEF2)EEF2 (TRANSLATION ELONGATION FACTOR, FUNCTIONAL TARGET)

Evidence

Reading pass · 3 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2019 TgPHYb is a 2-oxoglutarate-dependent prolyl hydroxylase required for optimal parasite growth and protein synthesis at high, but not low, O2 tensions, functioning as a sensor of elevated oxygen levels. Conditional expression strain (knockdown) with growth and invasion assays under varying oxygen conditions mBio Medium 30914506
2019 TgPHYb promotes the activity of translation elongation factor eEF2; depletion of TgPHYb leads to hyper-phosphorylation and inactivation of eEF2, decreased rates of translational elongation, and reduced abundance of parasite adhesins. Conditional knockdown of TgPHYb with measurement of eEF2 phosphorylation status, translational elongation rates, and adhesin protein levels mBio Medium 30914506
2023 PHYb acts upstream of CDPK3 in a stress-response pathway: PHYb promotes eEF2 activity by preventing CDPK3-mediated hyper-phosphorylation of eEF2; in the absence of PHYb, eEF2 is hyper-phosphorylated by CDPK3, inhibiting eEF2 interaction with the ribosome and blocking translational elongation. Genetic epistasis (CDPK3 loss-of-function in extracellularly stressed parasites), eEF2 phosphorylation assays, and co-immunoprecipitation of CDPK3 with eEF2 mSphere Medium 37272703

Source papers

Stage 0 corpus · 2 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 A Toxoplasma Prolyl Hydroxylase Mediates Oxygen Stress Responses by Regulating Translation Elongation. mBio 15 30914506
2023 Identification of Toxoplasma calcium-dependent protein kinase 3 as a stress-activated elongation factor 2 kinase. mSphere 5 37272703