RPT3

RPT3 (PF3D7_0413600) is a component of the 19S regulatory particle of the 26S proteasome that also carries out a moonlighting regulatory function in phosphatase signaling, as established through work on its P. berghei ortholog (PMID:41373862). In P. berghei, RPT3 directly binds the Protein Phosphatase 1 catalytic subunit (PP1c) via RVxF motifs and enhances PP1c activity both in vitro and in a Xenopus oocyte heterologous system, with this interaction and regulatory effect occurring outside the proteasome context; RPT3's ATP-binding capacity contributes to this phosphatase regulatory activity (PMID:41373862). Reverse genetic studies in P. berghei indicate that RPT3 is essential during the erythrocytic cycle, and interactome analysis confirms both its membership in the 19S regulatory particle and potential association with phospholipid-binding proteins (PMID:41373862). Beyond these findings in the P. berghei ortholog, no further mechanistic detail specific to PF3D7_0413600 has been characterized in the available corpus.

1. 2025 Medium

   Whether RPT3 functions only as a proteasome subunit or also acts independently was unknown; showing direct PP1c binding via RVxF motifs and enhancement of phosphatase activity outside the proteasome established a moonlighting regulatory role.

   Evidence Co-immunoprecipitation/binding assay, in vitro phosphatase activity assay, Xenopus oocyte heterologous expression, and RVxF motif mutagenesis on the P. berghei ortholog

   PMID:41373862

   Open questions at the time

   • Demonstrated in the P. berghei ortholog rather than P. falciparum PF3D7_0413600 directly
   • Single lab, single paper without independent replication
   • The physiological substrates and downstream signaling consequences of RPT3-enhanced PP1c activity are not defined
2. 2025 Medium

   Whether RPT3 is required for parasite growth and how it associates within the proteasome was unresolved; reverse genetics and interactome analysis established its essentiality during the erythrocytic cycle and confirmed its place in the 19S regulatory particle.

   Evidence Attempted gene knockout/knockdown reverse genetics with phenotypic readout plus interactome mass spectrometry in the P. berghei ortholog

   PMID:41373862

   Open questions at the time

   • Shown in the P. berghei ortholog, not directly in P. falciparum PF3D7_0413600
   • The functional significance of the potential interaction with phospholipid-binding proteins is not characterized
   • Essentiality was inferred from failed disruption rather than conditional depletion with a defined stage-specific arrest

• It remains unknown whether the PP1c-regulatory moonlighting function and 19S proteasome roles of RPT3 are conserved in P. falciparum PF3D7_0413600 itself and what its endogenous phosphatase substrates and physiological outputs are.
• No direct experimental characterization of P. falciparum PF3D7_0413600
• No identified downstream substrates of the RPT3-PP1c regulatory axis
• No structural model of the RPT3-PP1c interaction