PF3D7_1356600

PF3D7_1356600 (PfRCC-PIP) is an RCC1-motif-containing regulatory protein of Plasmodium falciparum that functions as a phosphatase-anchoring partner of the parasite Protein Phosphatase type-1 (PfPP1), which it binds directly in vitro and forms a complex with in the parasite (PMID:30429842). In a heterologous Xenopus oocyte system, PfRCC-PIP interacts with endogenous PP1 and synergizes with suboptimal progesterone to promote oocyte maturation, indicating it acts as a positive regulator of PP1 activity (PMID:30429842). Its RCC1-motif region additionally binds the parasite calcium-dependent protein kinase CDPK7, positioning PfRCC-PIP as a scaffold that could coordinate both kinase and phosphatase activities (PMID:30429842), and attempted knock-out failed to yield viable parasites, consistent with an essential role (PMID:30429842). Beyond these interaction and viability findings from a single study, no further mechanistic detail — substrate specificity, structural basis of binding, or in-parasite regulatory targets — has been characterized in the available corpus.

1. 2018 Medium

   Established that PF3D7_1356600 is a direct binding partner of the parasite phosphatase PfPP1, defining its first molecular interaction and its identity as a phosphatase-associated protein.

   Evidence In vitro binding assay and co-immunoprecipitation from P. falciparum lysate

   PMID:30429842

   Open questions at the time

   • The binding interface and RCC1-motif requirement for PfPP1 interaction were not mapped by mutagenesis
   • Stoichiometry and other components of the parasite PfPP1 complex are undefined
   • No in-parasite dephosphorylation substrate was identified
2. 2018 Medium

   Addressed whether the PfPP1 interaction is merely structural or regulatory, showing PfRCC-PIP activates PP1 in a functional context.

   Evidence Xenopus oocyte maturation assay with endogenous PP1 and suboptimal progesterone doses

   PMID:30429842

   Open questions at the time

   • Activation was shown against Xenopus PP1 in a heterologous system, not against PfPP1 in the parasite
   • The biochemical mechanism of PP1 activation (versus canonical inhibition) is unresolved
   • No direct phosphatase activity measurement on defined substrates
3. 2018 Low

   Extended the protein's role beyond phosphatase anchoring by identifying a kinase partner, raising the possibility of a dual scaffolding function.

   Evidence Pulldown/binding assay of the RCC1-motif-containing region with the kinase CDPK7

   PMID:30429842

   Open questions at the time

   • Single interaction assay with a protein fragment, no mutagenesis or orthogonal/reciprocal validation
   • Whether PfPP1 and CDPK7 bind simultaneously or competitively is unknown
   • Functional consequence of the CDPK7 interaction in the parasite is untested
4. 2018 Low

   Assessed the biological importance of the gene, indicating it is required for blood-stage parasite viability.

   Evidence Reverse genetics / attempted gene knock-out (failure to recover viable KO parasites)

   PMID:30429842

   Open questions at the time

   • Negative-selection inference from failure to obtain KO; no conditional knock-out or complementation to confirm essentiality
   • The essential cellular process the protein supports is not defined
   • Stage-specific requirements were not examined

• It remains unknown how PfRCC-PIP coordinates PfPP1 and CDPK7 activities in the parasite, what phosphoprotein substrates it governs, and whether its scaffolding function underlies its essentiality.
• No in-parasite substrate or dephosphorylation/phosphorylation target identified
• No structural model or mapped binding interfaces
• Localization and cell-cycle timing of the protein not characterized in the corpus