GEP

GEP (PF3D7_0515600; ortholog PBANKA_1115200) is a Plasmodium gametocyte protein required for gamete egress and male exflagellation during the transition to mosquito-stage development (PMID:32352241). It is expressed in gametocytes of both sexes and partially localizes to osmiophilic bodies; its genetic deletion in P. berghei causes aberrant rupture of the parasitophorous vacuole membrane and erythrocyte membrane, delayed osmiophilic body discharge, and immotile axonemes in male flagellar gametes, rendering both male and female null parasites unable to establish mosquito infection (PMID:32352241). In P. yoelii, GEP is likewise required for erythrocyte membrane rupture in both sexes and for axoneme assembly in males, and its expression in males depends on the RBPm1-driven axonemal intron splicing program, established by intron-insertion experiments that abolished GEP expression in the absence of RBPm1 (PMID:38824128). Post-translationally, GEP sits within the calcium-signaling machinery of gametogenesis: it is hypophosphorylated in P. falciparum cdpk4-null gametocytes and behaves as a PfCDPK4 substrate candidate in vitro (PMID:34724830), and in P. berghei it is ubiquitinated in an SCF-FBXO1-dependent manner that is negatively regulated by CDPK1 (PMID:36898988). Beyond these regulatory links, the biochemical activity of the GEP protein itself is uncharacterized in the available corpus.

1. 2020 High

   Establishing whether GEP has a cellular function in sexual development, the first knockout defined it as a pleiotropic egress and exflagellation factor rather than a passive gametocyte marker.

   Evidence Targeted gene deletion in P. berghei with OB localization microscopy, genetic crossing, and mosquito transmission assays

   PMID:32352241

   Open questions at the time

   • biochemical activity of GEP and how it drives membrane rupture is unknown
   • molecular basis of OB targeting not defined
   • how GEP contributes to axoneme motility is not resolved
2. 2021 Medium

   To place GEP within gametogenesis signaling, phosphoproteomics identified it as a CDPK4-dependent phosphoprotein, linking it to the calcium cascade that triggers male gametogenesis.

   Evidence Quantitative phosphoproteomics of wild-type vs. Pfcdpk4-null P. falciparum gametocytes plus in vitro kinase assay

   PMID:34724830

   Open questions at the time

   • direct vs. indirect substrate relationship not fully reconstituted
   • phosphosites and their functional consequence for GEP not mapped
3. 2022 Low

   A PP1-LRR1 interactome survey raised the possibility that GEP is embedded in a phosphatase regulatory network during sexual development.

   Evidence Immunoprecipitation-mass spectrometry of PbLRR1 in P. berghei

   PMID:35920043

   Open questions at the time

   • single Co-IP/MS with no GEP-specific functional follow-up or reciprocal validation
   • whether GEP is a PP1 substrate or bystander is unknown
4. 2023 Medium

   Ubiquitinomics extended GEP regulation beyond phosphorylation, showing it is an SCF-FBXO1 ubiquitination target under antagonistic control by CDPK1.

   Evidence Ubiquitinomic and comparative proteomic mass spectrometry of FBXO1-depleted and CDPK1-KO P. berghei parasites

   PMID:36898988

   Open questions at the time

   • GEP ubiquitination not directly reconstituted
   • consequence of ubiquitination for GEP stability or activity not established
5. 2024 High

   Cross-species knockout and intron-insertion experiments confirmed GEP's egress/axoneme role in P. yoelii and defined RBPm1-dependent intron splicing as the mechanism controlling its male-specific expression.

   Evidence Δgep deletion, axonemal-intron insertion reporter lines, and immunofluorescence phenotyping in P. yoelii 17XNL, across three independent experiments

   PMID:38824128

   Open questions at the time

   • does not define GEP's biochemical role in membrane rupture or axoneme assembly
   • how RBPm1-dependent splicing intersects with the CDPK4/FBXO1 post-translational controls is unknown
6. 2024 Low

   Proximity proteomics placed GEP near the DOZI/CITH/ALBA translational repression machinery, hinting that GEP transcript or protein is controlled by pre-fertilization mRNP storage in females.

   Evidence TurboID proximity proteomics with DOZI and ALBA4 baits in P. yoelii gametocytes and zygotes

   PMID:39777415

   Open questions at the time

   • single proximity-labeling dataset with no GEP-specific functional follow-up
   • whether GEP mRNA is a bona fide repressed transcript is untested

• The intrinsic biochemical activity of the GEP protein — how it mechanistically drives parasitophorous vacuole/erythrocyte membrane rupture and supports axoneme motility — remains unresolved.
• no molecular activity assigned to GEP
• no structural model
• direct binding partners that execute egress not identified