MSRP1

MSRP1 (PF3D7_1335000) is a member of the P. falciparum MSP7-like multigene family on chromosome 13 whose members were identified through their ability to bind the amino-terminal region of MSP-1; recombinant MSRP1 interacts directly with the MSP-1 N-terminus in vitro and colocalizes with MSP-1 on the trophozoite surface (PMID:12477792). In asexual blood stages, MSRP1 mRNA is barely detectable and no specific protein is seen by antibody, and deletion of msrp1 produces no detectable growth or invasion phenotype, indicating it is dispensable for asexual proliferation (PMID:20472690). MSRP family members, including MSRP1, are PEXEL/HT-negative exported proteins (PNEPs) trafficked into the host erythrocyte, implying functions beyond the merozoite surface (PMID:23950716). MSRP1 expression is a transcriptional output of the sexual-commitment pathway: it requires the master gametocytogenesis factor AP2-G, is abolished in a non-DNA-binding AP2-G mutant, and distinguishes early from late sexually committed schizonts (PMID:40568120, PMID:41547993). Beyond these observations, the specific molecular function of the MSRP1 protein itself has not been characterized in the available corpus.

1. 2002 Medium

   The unknown was whether MSRP1 has any biochemical partner; identifying it as an MSP-1 N-terminus binder placed it in the MSP7-like family and linked it physically to the merozoite surface complex.

   Evidence Yeast two-hybrid screen, in vitro binding assay, and immunofluorescence colocalization with MSP-1 on trophozoites

   PMID:12477792

   Open questions at the time

   • No reciprocal co-IP or structural validation of the MSRP1–MSP-1 interaction
   • Functional consequence of the interaction not tested
   • Binding shown in vitro; native complex not demonstrated
2. 2010 Medium

   It was unknown whether MSRP1 is required for asexual growth; systematic knockout showed its very low expression and complete dispensability, redirecting attention away from an essential asexual role.

   Evidence RT-PCR, hybridization, Western blot with recombinant-protein antibodies, and targeted gene disruption with growth/invasion assays in P. falciparum 3D7

   PMID:20472690

   Open questions at the time

   • Does not address a role in stages other than asexual blood stage
   • Low protein detection leaves native localization and abundance unresolved
   • Redundancy with other family members not excluded
3. 2013 Medium

   The unknown was where MSRP proteins act; showing that MSRP family members are PNEPs exported into the host cell established that their function extends beyond the merozoite surface into the infected erythrocyte.

   Evidence Reporter-based export assays, immunofluorescence/live imaging, and protein fractionation

   PMID:23950716

   Open questions at the time

   • MSRP1 not distinguished from other MSRP family members in the export assays
   • Host-cell function of exported MSRP1 not defined
   • No identified exported-protein partner
4. 2015 Low

   The unknown was whether MSP7-like proteins engage host endothelial receptors; the P. berghei ortholog PbMSRP1 was shown to bind mouse P-selectin, hinting at a host-interaction role for the family.

   Evidence Extracellular protein interaction screen and biochemical binding assays for PbMSRP1 (P. berghei) and PfMSP7 (P. falciparum)

   PMID:26045295

   Open questions at the time

   • Interaction shown for the P. berghei ortholog, not directly for PF3D7_1335000
   • Single method for the MSRP1 ortholog; not reciprocally validated
   • Functional relevance in P. falciparum untested
5. 2019 Low

   The unknown was how MSRP1 relates to sexual commitment; correlation of high msrp1 expression with high gametocyte conversion in field isolates placed it within the GDV1-AP2-G commitment program.

   Evidence Gametocyte conversion assays combined with gene expression analysis of clinical P. falciparum samples

   PMID:31086187

   Open questions at the time

   • Correlation only; no direct functional experiment on MSRP1
   • Cannot distinguish cause from co-regulation
   • Field-sample heterogeneity uncontrolled
6. 2025 Medium

   The unknown was whether MSRP1 expression is directly controlled by the sexual-commitment master regulator; abolition of MSRP1 in a non-DNA-binding AP2-G mutant established it as an AP2-G transcriptional target and a marker of early committed schizonts.

   Evidence CRISPR/Cas9 point-mutation editing of AP2-G (V2163L) with immunofluorescence/reporter readout of MSRP1 expression

   PMID:40568120 PMID:41547993

   Open questions at the time

   • Direct AP2-G binding to the msrp1 promoter not demonstrated
   • Functional role of MSRP1 in gametocytogenesis not tested
   • Whether MSRP1 acts in the erythrocyte or gametocyte compartment unresolved

• The molecular function of the MSRP1 protein during sexual commitment and after export into the host erythrocyte remains undefined.
• No demonstrated function for the exported MSRP1 protein
• No gametocyte-stage phenotype for msrp1 deletion
• No native binding partner confirmed for PF3D7_1335000 itself beyond in vitro MSP-1 binding