UBP1

PF3D7_0104300 (UBP1) is a large Plasmodium deubiquitinating enzyme whose catalytic activity governs ubiquitin signaling required for host-cell cytosol endocytosis and is essential for parasite survival (PMID:39909372, PMID:34309894). Recombinant P. falciparum UBP1 cleaves ubiquitin with defined linkage specificity, and resistance-associated point mutations reduce this catalytic activity (PMID:39909372). UBP1 functions within the K13/AP-2μ/Coronin endocytic pathway that captures host haemoglobin in ring-stage parasites, such that its perturbation limits haemoglobin-derived heme and thereby reduces artemisinin activation (PMID:38700363, PMID:34309894). Mutations in UBP1 lower early ring-stage susceptibility to artemisinin: in P. falciparum the V3275F variant elevated dihydroartemisinin survival in the ring-stage survival assay without altering susceptibility to other drugs (PMID:31636063), and in P. berghei the V2721F mutation reduced artemisinin susceptibility in vivo (PMID:32340987). Distinct UBP1 mutations also confer chloroquine and multidrug tolerance; in P. yoelii, I1560N/P2874T mutations impaired UBP1 cytoplasmic aggregation and deubiquitinating activity, raised cellular ubiquitination, and relocalized the MDR1 transporter from the digestive vacuole to the plasma membrane to enhance drug efflux and confer resistance to mefloquine, lumefantrine, and piperaquine, reversible by MDR1 inhibition (PMID:38413566). These resistance mutations carry substantial fitness costs, and a UBP1 R3138H mutation combined with K13 C580Y did not increase artemisinin resistance beyond K13 alone, consistent with UBP1 and K13 acting in the same pathway (PMID:38700363). Beyond its role in this endocytic pathway and its enzymatic activity, no additional substrates or structural details of UBP1 have been characterized in the available corpus.

1. 2007 Medium

   Establishing whether a deubiquitinating enzyme could influence antimalarial drug response, this work first linked UBP1 mutations to altered chloroquine and artemisinin sensitivity.

   Evidence Linkage Group Selection from a genetic cross with drug pressure and structural homology mapping in P. chabaudi

   PMID:17581118

   Open questions at the time

   • Functional mechanism not biochemically reconstituted
   • Mutations mapped by homology, not on the native protein structure
   • No demonstration that UBP1 acts in an endocytic pathway
2. 2019 High

   To test causality directly, isogenic P. falciparum lines showed that a specific UBP1 variant reduces early ring-stage artemisinin survival, establishing UBP1 as a determinant of the ring-stage resistance phenotype.

   Evidence CRISPR-Cas9 gene editing and ring-stage survival assay with drug-susceptibility controls in P. falciparum

   PMID:31636063

   Open questions at the time

   • V3306F did not confer the phenotype, so variant-specificity is not fully explained
   • No effect on 48-hour exposure, leaving the stage-specific mechanism undefined
   • Enzymatic consequence of the mutation not measured
3. 2020 High

   In vivo genetic dissection distinguished distinct UBP1 mutations conferring artemisinin versus chloroquine phenotypes and demonstrated reversibility and fitness cost, strengthening the causal link.

   Evidence CRISPR-Cas9 knock-in, in vivo drug assays, and genetic reversal experiments in P. berghei

   PMID:32340987

   Open questions at the time

   • Lethality of combined mutations not mechanistically explained
   • Molecular basis of the growth defect not resolved
   • Enzymatic activity of mutants not measured
4. 2021 Medium

   Placing UBP1 within a defined cellular pathway, synthesis of genetic evidence positioned it alongside K13, AP-2μ, and Coronin in ring-stage haemoglobin endocytosis, providing a mechanistic rationale for artemisinin tolerance via reduced heme-dependent drug activation.

   Evidence Review synthesizing genetic epistasis and functional data across primary P. falciparum studies

   PMID:34309894

   Open questions at the time

   • Pathway placement inferred from convergent genetics, not direct interaction data for UBP1
   • Direct role of UBP1 deubiquitination in endocytosis not demonstrated here
   • Substrates of UBP1 in the pathway unknown
5. 2024 High

   Mechanistic dissection in P. yoelii connected UBP1 catalytic function to a downstream effector, showing that loss of UBP1 activity relocalizes MDR1 to enhance drug efflux and confer multidrug resistance.

   Evidence Drug selection, allelic exchange, deubiquitinating activity assay, subcellular localization, and MDR1 inhibitor rescue in P. yoelii

   PMID:38413566

   Open questions at the time

   • Whether MDR1 is a direct UBP1 substrate is not established
   • Mechanism linking UBP1 aggregation to its activity unresolved
   • Extent to which this pathway operates identically in human-infective P. falciparum unknown
6. 2024 Medium

   Epistasis with K13 clarified that UBP1 acts within the same endocytic pathway rather than an independent axis, since combining UBP1 R3138H with K13 C580Y did not additively increase resistance, at high fitness cost.

   Evidence Isogenic parasite construction, ring-stage survival assays, K13 titration, and growth competition in P. falciparum

   PMID:38700363

   Open questions at the time

   • Single-lab isogenic lines only
   • Molecular basis of the disproportionate fitness cost not resolved
   • Direct physical association of UBP1 with K13 compartment neighbors not shown
7. 2025 High

   Biochemical reconstitution finally defined UBP1 as a bona fide deubiquitinase with linkage specificity and confirmed its essentiality, showing resistance mutations reduce catalytic activity.

   Evidence In vitro deubiquitinating activity and linkage-specificity assays, resistance-associated mutagenesis, and parasite fitness assays with recombinant P. falciparum UBP1

   PMID:39909372

   Open questions at the time

   • Physiological substrates of UBP1 not identified
   • No structural model of the enzyme reported
   • Direct mechanistic link between deubiquitination and endocytic function not reconstituted

• The physiological ubiquitinated substrates of UBP1 and the molecular route by which its deubiquitinating activity drives host-cell cytosol endocytosis remain unresolved.
• No direct substrate of UBP1 identified in the corpus
• Mechanism coupling UBP1 activity to endocytic machinery unknown
• No structural characterization of the enzyme