PF3D7_0629800

PF3D7_0629800 (PfCullin-2) is the scaffold subunit of a functional CRL4-like cullin-RING E3 ubiquitin ligase (PfCRL4) in Plasmodium falciparum, assembling with PfRbx1, a cleavage and polyadenylation specificity factor subunit, and WD40 repeat proteins into a complex with demonstrated in vitro ubiquitination activity (PMID:38416790). Like canonical cullins, PfCullin-2 is regulated by neddylation: it was recovered as a physiological substrate of PfNEDD8 in P. falciparum (PMID:33214620). The protein is expressed predominantly in erythrocytic trophozoite and schizont stages and shows nucleocytoplasmic localization with chromatin association (PMID:38416790). Functionally, PfCullin-2/PfCRL4 is required for asexual and sexual erythrocytic development; its depletion reduces the number of nuclei per parasite and produces poorly delimited merozoites and aberrant internal membranes in schizonts, implicating the complex in nuclear division during schizogony and in merozoite membrane integrity (PMID:38416790). Proteomic profiling after knock-down shows altered levels of proteins in translation and folding, lipid biosynthesis and transport, DNA replication, and protein degradation pathways (PMID:38416790), though the direct ubiquitination substrates of PfCRL4 have not been identified in the available corpus.

1. 2020 Medium

   Establishing whether PfCullin-2 is post-translationally regulated addressed whether Plasmodium cullins use the conserved neddylation switch that activates cullin-RING ligases.

   Evidence IP-MS of tagged wild-type PfNEDD8 in P. falciparum with heterologous complementation in S. cerevisiae rub1Δ/ubc12Δ strains

   PMID:33214620

   Open questions at the time

   • Does not define the sites or functional consequence of neddylation on PfCullin-2 activity
   • Does not distinguish PfCullin-2 from the second putative cullin also recovered
2. 2024 High

   Identifying the composition and catalytic activity of the PfCullin-2 complex answered whether it forms a bona fide E3 ligase and defined its subunit architecture.

   Evidence Immunoprecipitation, sequence analysis, and in vitro ubiquitination assay in P. falciparum

   PMID:38416790

   Open questions at the time

   • Physiological ubiquitination substrates of PfCRL4 not identified
   • Role of the CPSF subunit and WD40 proteins as substrate receptors not resolved
3. 2024 Medium

   Localization at trophozoite and schizont stages placed PfCullin-2 activity in the nucleus/cytoplasm and on chromatin, linking the complex to nuclear processes during erythrocytic development.

   Evidence Tagged-parasite fluorescence imaging and subcellular fractionation in P. falciparum

   PMID:38416790

   Open questions at the time

   • Chromatin association not mapped to specific genomic loci or substrates
   • Single lab, single study
4. 2024 High

   Conditional depletion defined the essential cellular role of PfCullin-2, showing it is required for nuclear division and merozoite membrane integrity during schizogony.

   Evidence Conditional protein knock-down with morphological analysis and nuclei-per-parasite quantification in P. falciparum

   PMID:38416790

   Open questions at the time

   • Mechanistic link between ligase activity and the nuclear-division/membrane defects not established
   • Sexual-stage requirement described but not mechanistically dissected
5. 2024 Medium

   Proteomics after knock-down provided the first systems-level view of pathways downstream of PfCullin-2, but did not establish which changes are direct.

   Evidence Quantitative proteomics after conditional PfCullin-2 knock-down in P. falciparum

   PMID:38416790

   Open questions at the time

   • Cannot distinguish direct ubiquitination targets from downstream secondary effects
   • No target validated as a CRL4 substrate

• The direct ubiquitination substrates of PfCRL4 and how substrate selection is coupled to nuclear division and merozoite membrane biogenesis remain unknown.
• No physiological substrate identified
• Mechanism connecting E3 activity to schizogony phenotypes unresolved
• No structural model of the PfCRL4 assembly