MSP7A

MSRP2 (PBANKA_1349000) is an MSP7-like protein of malaria parasites associated with the schizont/merozoite surface and with the MSP-1 complex during blood-stage development (PMID:12477792, PMID:14742548). In the P. yoelii ortholog, MSRP2 interacts with the amino-terminal region of MSP-1, co-localizes with the N-terminal portion of MSP-1 and with MSP-7 on the schizont surface, and is released into culture supernatants (PMID:12477792, PMID:14742548). In P. falciparum, MSRP2 diverges from MSP7 in fate: it is absent from mature merozoites and is instead sequentially proteolytically processed into 28- and 25-kDa forms, with the mature 25-kDa species being soluble and secreted upon merozoite egress (PMID:20472690); this processing is attributed to the subtilisin-like serine protease PfSUB1 (PMID:21220481). In P. berghei, MSRP2 additionally binds host mouse P-selectin through the receptor's C-type lectin and EGF-like domains (PMID:26045295). No individual functional requirement has been assigned to MSRP2: deletion of msrp2 within a P. berghei triple mutant produced no detectable life-cycle defect (PMID:26222913), and the biological consequence of its MSP-1 association, secretion, and P-selectin binding has not been resolved in the available corpus.

1. 2002 Medium

   Establishing that MSRP2 physically engages the MSP-1 machinery answered whether this MSP7-like protein belongs to the merozoite surface protein complex rather than acting independently.

   Evidence Yeast two-hybrid screen and in vitro binding assays with the P. yoelii MSP-1 N-terminus

   PMID:12477792

   Open questions at the time

   • Binding interface on MSRP2 not mapped
   • Functional consequence of the MSP-1 interaction not tested
   • Shown only for the P. yoelii ortholog
2. 2004 Medium

   Localizing MSRP2 to the schizont surface alongside MSP-1 and MSP-7 and detecting its release established where and when it acts during blood-stage development.

   Evidence Immunoprecipitation and immunofluorescence co-localization in P. yoelii 17XL

   PMID:14742548

   Open questions at the time

   • Mechanism and timing of release not defined
   • Whether release reflects processing not addressed here
   • Single ortholog studied
3. 2010 Medium

   Showing that P. falciparum MSRP2 is processed into a soluble secreted 25-kDa form and is absent from merozoites distinguished its fate from the surface-retained MSP7, reframing MSRP2 as a secreted rather than surface-anchored protein.

   Evidence Western blot with anti-MSRP2 antibodies and fractionation of P. falciparum 3D7 merozoites and egress supernatants

   PMID:20472690

   Open questions at the time

   • Function of the secreted 25-kDa form unknown
   • Fate of the 28-kDa intermediate not resolved
   • Divergence from MSP7 fate not explained mechanistically
4. 2011 Medium

   Identifying PfSUB1 as the protease that cleaves MSRP2 connected its processing to the egress protease cascade, giving a molecular basis for the sequential cleavage observed.

   Evidence Proteomic and bioinformatic analysis of SUB1 cleavage sites in the P. falciparum late asexual proteome

   PMID:21220481

   Open questions at the time

   • Cleavage not reconstituted with purified enzyme and substrate
   • Order and sites of the two cleavages not resolved
   • Contribution of other proteases not excluded
5. 2015 Medium

   Demonstrating that P. berghei MSRP2 binds host P-selectin raised the possibility of a host-interaction role distinct from its intra-parasite MSP-1 association.

   Evidence AVEXIS extracellular interaction screen with biochemical mapping to P-selectin C-type lectin and EGF-like domains in P. berghei

   PMID:26045295

   Open questions at the time

   • In vivo relevance of P-selectin binding not shown
   • Whether the secreted or surface form mediates binding unclear
   • Affinity and physiological setting undefined
6. 2015 Low

   Deleting msrp2 tested whether it is required for parasite development; the absence of a phenotype in a triple mutant indicated no individually essential life-cycle role under the conditions tested.

   Evidence Targeted gene disruption and life-cycle analysis of a P. berghei msp7/msrp1/msrp2 triple knockout

   PMID:26222913

   Open questions at the time

   • Contribution of MSRP2 alone cannot be separated from the triple deletion
   • Possible redundancy with family members not resolved
   • Subtle or condition-specific phenotypes not excluded

• It remains unknown what biological function MSRP2 serves given its secretion, MSP-1 association, and P-selectin binding, and whether these roles are conserved or divergent across Plasmodium species.
• No single-gene knockout phenotype defined
• No mechanistic link between MSP-1 binding, secretion, and P-selectin binding
• Species divergence in fate (surface vs secreted) not reconciled