PF3D7_1422900

Pf14-3-3I (PF3D7_1422900) is a P. falciparum 14-3-3 protein that functions as a scaffolding adaptor coupling an AKAP-like protein to the cAMP/PKA signaling machinery in the asexual blood stage (PMID:27129434). In P. falciparum 3D7, it physically associates with the AKAP-like protein PfAKAL, with which it colocalizes in the parasite (PMID:27129434), and it independently binds the PKA regulatory subunit PfPKA-R, positioning it as an indirect bridge that links PfAKAL to PKA rather than PfAKAL contacting PKA-R directly (PMID:27129434). Pf14-3-3I is itself a PKA substrate, being phosphorylated in vitro by PKA whereas PfAKAL is not, implying that PKA-mediated phosphorylation regulates Pf14-3-3I-containing complexes (PMID:27129434). Beyond these interaction and phosphorylation findings, no further mechanistic detail — including the functional consequence of the interactions in vivo, the phosphosite involved, or any essentiality data for PF3D7_1422900 — has been characterized in the available corpus.

1. 2016 Medium

   Establishing that Pf14-3-3I directly binds the AKAP-like protein PfAKAL identified the first molecular partner of this 14-3-3 protein and placed it within an anchoring-protein context.

   Evidence Reciprocal pull-down with recombinant proteins and parasite extracts plus immunofluorescence colocalization in P. falciparum 3D7

   PMID:27129434

   Open questions at the time

   • Does not define the binding interface or whether the interaction is phosphorylation-dependent
   • Functional consequence of the PfAKAL association in vivo is not established
   • Colocalization does not resolve the subcellular compartment
2. 2016 Medium

   Demonstrating that Pf14-3-3I also binds the PKA regulatory subunit PfPKA-R answered how PfAKAL connects to PKA, casting Pf14-3-3I as an indirect bridge rather than PfAKAL binding PKA-R directly.

   Evidence Pull-down assay with biochemical/proteomic interaction analysis in P. falciparum 3D7

   PMID:27129434

   Open questions at the time

   • Ternary complex of PfAKAL–Pf14-3-3I–PfPKA-R not directly reconstituted
   • Whether the two interactions are simultaneous or mutually exclusive is unresolved
   • In vivo relevance to cAMP/PKA signaling not demonstrated
3. 2016 Medium

   Showing Pf14-3-3I is phosphorylated by PKA in vitro (while PfAKAL is not) identified a candidate regulatory mechanism controlling Pf14-3-3I-containing complexes.

   Evidence Radiolabel in vitro kinase activity assay with PKA as the writer

   PMID:27129434

   Open questions at the time

   • In vitro kinase assay does not confirm phosphorylation occurs in the parasite
   • Phosphosite(s) not mapped
   • Effect of phosphorylation on PfAKAL or PfPKA-R binding not tested

• The physiological role of Pf14-3-3I in asexual development and the functional output of its bridging of PfAKAL to PKA remain unknown.
• No knockout or knockdown phenotype for PF3D7_1422900
• No structure of the complex or defined binding motifs
• No demonstration that PKA phosphorylation of Pf14-3-3I alters complex assembly or signaling in vivo