LRR12

LRR12 (PfLRR1, PF3D7_1249600) is a leucine-rich repeat protein of Plasmodium falciparum that functions as a regulator of the protein phosphatase PfPP1: it physically binds PfPP1 in vitro and in parasite extracts and inhibits PfPP1 phosphatase activity (PMID:16629662). Consistent with this inhibitory role, expression of LRR12 in Xenopus oocytes engages endogenous PP1 and drives progression through the G2/M checkpoint, inducing germinal vesicle breakdown as expected for relief of PP1 activity (PMID:16629662). Its transcript accumulates in late intraerythrocytic stages (late trophozoites and schizonts) (PMID:17689674). Beyond its role as a PfPP1-binding inhibitor and this stage-specific expression, no further mechanistic detail for PF3D7_1249600 has been characterized in the available corpus.

1. 2006 Medium

   Establishing whether LRR12 acts on the PfPP1 phosphatase answered whether this LRR protein is a bona fide phosphatase regulator rather than an uncharacterized structural protein.

   Evidence GST pull-down and co-immunoprecipitation from parasite extracts plus in vitro phosphatase assay in P. falciparum

   PMID:16629662

   Open questions at the time

   • The domain of LRR12 mediating PfPP1 binding was not mapped
   • Whether the interaction is regulated during the parasite life cycle was not addressed
   • No structural model of the LRR12–PfPP1 complex
2. 2006 Medium

   Testing LRR12 in a heterologous cell-cycle system answered whether its PfPP1 inhibition has a functional cellular consequence, showing it can override a G2/M checkpoint.

   Evidence Xenopus oocyte GVBD functional assay with anti-PP1 antibody and okadaic acid controls

   PMID:16629662

   Open questions at the time

   • Activity shown only in a heterologous Xenopus system, not in the parasite
   • The physiological cell-cycle role of LRR12 in P. falciparum was not demonstrated
   • No genetic loss-of-function in the parasite
3. 2007 Low

   Profiling LRR12 transcript timing answered when in the intraerythrocytic cycle it is expressed, placing peak abundance in late trophozoites and schizonts.

   Evidence Real-time quantitative PCR of cloned cDNA from P. falciparum

   PMID:17689674

   Open questions at the time

   • Transcript data only; protein-level expression not confirmed
   • No functional consequence tied to the stage-specific expression
   • Single method, single lab

• Whether LRR12 is essential for P. falciparum intraerythrocytic development and how PfPP1 inhibition by LRR12 is regulated in the parasite remain unresolved.
• No parasite genetic knockout or conditional knockdown of PF3D7_1249600
• PfPP1 substrates dephosphorylated in an LRR12-dependent manner are unidentified
• No structural basis for the inhibitory interaction