PPM2A

PPM2A is a PPM-family serine/threonine phosphatase of Toxoplasma gondii that contributes to tachyzoite fitness while being dispensable for the core intracellular replication cycle (PMID:39461506). Endogenous C-terminal tagging localizes the protein throughout the whole tachyzoite rather than to a discrete compartment (PMID:39461506), and it falls within the parasite Calmodulin interaction network (PMID:39461506). Genetic ablation of PPM2A, of the related PPM2B, or of both together leaves intracellular replication and acute virulence in mice intact, yet reduces plaque size, indicating a fitness contribution independent of the replication defect (PMID:39461506). Beyond these observations, the enzyme's substrates, catalytic regulation, and the functional consequence of the Calmodulin association have not been characterized in the available corpus.

1. 2024 Medium

   To place PPM2A in a cellular context, its subcellular distribution was resolved, establishing that the phosphatase is not restricted to a single organelle but spread throughout the tachyzoite.

   Evidence Endogenous C-terminal 10HA tagging and immunofluorescence in RHΔku80

   PMID:39461506

   Open questions at the time

   • Whole-cell signal does not resolve whether PPM2A concentrates at any structure under specific cell-cycle or stress conditions
   • Single tag, single method, no orthogonal localization
2. 2024 Low

   To identify functional partners, PPM2A was recovered in a Calmodulin proximity interactome, linking the phosphatase to calcium/calmodulin signaling machinery.

   Evidence BioID proximity proteomics for Toxoplasma Calmodulin (cited from prior study)

   PMID:39461506

   Open questions at the time

   • Single BioID screen with no reciprocal validation
   • Proximity labeling does not establish a direct or functionally relevant interaction
   • No demonstration that Calmodulin regulates PPM2A activity
3. 2024 Medium

   To test whether PPM2A is required for the lytic cycle, single and double knockouts of PPM2A and the paralog PPM2B were generated and phenotyped, showing the phosphatase is dispensable for replication and acute virulence but contributes to overall fitness.

   Evidence CRISPR-Cas9 knockout with replication, plaque, and mouse virulence assays in RHΔhxgprt

   PMID:39461506

   Open questions at the time

   • The step in the lytic cycle responsible for the plaque-size defect is not identified
   • No molecular explanation (substrate or pathway) for the fitness contribution
   • Functional redundancy between PPM2A and PPM2B not resolved by the double knockout phenotype

• The catalytic substrates of PPM2A, the mechanistic basis of its Calmodulin association, and the cellular process underlying its fitness contribution remain unknown.
• No phosphatase substrate identified
• No evidence that Calmodulin binding modulates catalytic activity
• No structural or biochemical characterization of the enzyme