PF3D7_0818200

PF3D7_0818200 (14-3-3I) is a phosphorylation-dependent scaffold protein of P. falciparum that reads phosphorylated ligands to organize both nuclear and merozoite signaling processes (PMID:23308157, PMID:32817103). In the nucleus it acts as a histone modification reader, binding recombinant parasite histones and preferentially recognizing histone H3S28ph over H3S10ph independent of neighboring modifications (PMID:23308157). At the invasive stage it assembles a multiprotein merozoite signaling complex by binding phosphorylated PfCDPK1 and phosphorylated PfPKAr, and disruption of this complex with a phosphopeptide based on the Ca2+-dependent phosphosites of PKAr blocks microneme secretion and red blood cell invasion (PMID:32817103). Its interaction with PfCDPK1 is a canonical Mode I (RXXpS/pT) engagement of the CDPK1 phosphosite 61KLGpS64 with an affinity of ~670 nM, and this binding marginally enhances CDPK1 kinase activity (PMID:32484216). PF3D7_0818200 also binds and colocalizes with the AKAP-like protein PfAKAL and bridges it to PfPKA-R; it is itself phosphorylated in vitro by PKA whereas PfAKAL is not, implying phosphorylation-regulated assembly of the PfAKAL–PF3D7_0818200–PfPKA-R complex (PMID:27129434). Beyond these scaffolding and reader roles, no further mechanistic detail has been characterized in the available corpus.

1. 2013 Medium

   Established that PF3D7_0818200 is a nuclear phosphorylation reader, addressing whether a parasite 14-3-3 protein could decode histone phosphomarks.

   Evidence Recombinant protein binding to purified parasite histones and a panel of H3 phosphopeptides, with in silico analysis of binding residues

   PMID:23308157

   Open questions at the time

   • Binding residues were not validated by mutagenesis
   • The downstream chromatin or transcriptional consequence of H3S28ph reading was not defined
   • Shown only in vitro; nuclear recruitment in living parasites not demonstrated
2. 2016 Medium

   Identified PF3D7_0818200 as a bridge in a PKA-associated complex, answering how an AKAP-like anchoring protein connects to the PKA regulatory subunit.

   Evidence Pull-downs with recombinant proteins and parasite extracts, immunofluorescence colocalization, and in vitro radiolabel PKA phosphorylation assay

   PMID:27129434

   Open questions at the time

   • Single-lab pull-down with limited mechanistic follow-up
   • Functional consequence of the PfAKAL–PF3D7_0818200–PfPKA-R complex not established
   • Whether PKA phosphorylation of PF3D7_0818200 gates complex assembly was not directly tested
3. 2020 High

   Defined PF3D7_0818200 as the organizer of a merozoite invasion-signaling complex, showing that its scaffolding of phospho-PfPKAr and phospho-PfCDPK1 is functionally required for invasion.

   Evidence Reciprocal co-immunoprecipitation, gel filtration, competitive phosphopeptide displacement, and microneme secretion and RBC invasion assays

   PMID:32817103

   Open questions at the time

   • The phosphopeptide disruption is pharmacological; genetic ablation of PF3D7_0818200 binding not shown
   • Temporal ordering of complex assembly during invasion not resolved
   • Full composition of the merozoite complex beyond the named partners not defined
4. 2020 High

   Resolved the molecular grammar and affinity of the PF3D7_0818200–PfCDPK1 interaction and its effect on kinase activity, providing a druggable interface.

   Evidence Molecular dynamics simulation with SPR, ITC and ELISA affinity measurements, kinase activity assay, and peptidomimetic antagonist growth-inhibition tests

   PMID:32484216

   Open questions at the time

   • The mechanism by which binding enhances CDPK1 activity is only marginal and mechanistically undefined
   • Cellular relevance of the 670 nM affinity during native signaling not established
   • Selectivity of peptidomimetic antagonists over sibling 14-3-3 members not characterized

• It remains unknown how the nuclear histone-reading role and the cytoplasmic merozoite signaling-scaffold role of PF3D7_0818200 are coordinated across the parasite life cycle.
• No genetic loss-of-function study connecting the two functional modules
• No structural model of PF3D7_0818200 bound to its native partners in the parasite
• Regulation of PF3D7_0818200 phosphorylation state in vivo not defined