PHB2

PF3D7_1014700 (PHB2) is an essential mitochondrial prohibitin of Plasmodium that maintains organellar integrity while also serving a moonlighting role at the host-parasite interface during invasion (PMID:37088154, PMID:39245193). In the parasite mitochondrion it partners with PfPHB1 to form a heterodimeric inner-membrane complex; expression of PfPHB2 complements PHB2-null yeast, restoring growth, stabilizing mitochondrial DNA, and preserving mitochondrial integrity, demonstrating conserved function (PMID:32883936, PMID:37088154). Endogenous tagging places PfPHB2 in the branched mitochondrion throughout the asexual cycle, and although its inducible knockdown alone is tolerated, depletion under mitochondrial stress (ClpQ AAA-protease inhibition) triggers ROS accumulation, loss of membrane potential, mitochondrial fragmentation, and apoptosis-like death, and sensitizes parasites to proguanil — defining an anti-apoptotic, stress-protective role (PMID:39245193). In P. berghei the gene is refractory to deletion, consistent with essentiality (PMID:29669282), and PfPHB2 is a nanomolar target of the anti-plasmodial compound rocaglamide-A (PMID:37088154). Separately, PfPHB2 is displayed on the merozoite surface, where it binds host erythrocyte Hsp70A1A to drive invasion, with knockdown of either partner blocking entry (PMID:38812541); the orthologous host reticulocyte PHB2 is also implicated as a co-receptor for the P. vivax ligand PvRBP1a (PMID:41078366).

1. 2018 Medium

   Establishing whether PHB2 is dispensable defined it as an essential mitochondrial factor, distinguishing it from the deletable prohibitin-like PHBL.

   Evidence Genetic deletion attempts and fluorescence localization in P. berghei

   PMID:29669282

   Open questions at the time

   • Essentiality inferred from failed deletion, not a conditional knockout
   • No molecular function assigned to PHB2 in this study
   • PHB2-specific phenotype is a negative (non-deletable) result
2. 2020 Low

   Identifying the PfPHB2-PfPHB1 interaction proposed that Plasmodium builds a canonical prohibitin heterodimeric complex analogous to the mitochondrial inner-membrane assembly.

   Evidence Yeast two-hybrid and homology modelling in P. falciparum

   PMID:32883936

   Open questions at the time

   • Single interaction method (yeast two-hybrid) without in-parasite biochemical validation
   • Supercomplex stoichiometry and architecture not resolved
3. 2023 Medium

   Functional complementation in yeast and drug-target validation demonstrated PfPHB2 is a conserved mitochondrial prohibitin maintaining mtDNA and a target of rocaglamide-A.

   Evidence Immunofluorescence, co-IP with PfPHB1, PHB2-null yeast complementation, mtDNA stability assay, and Roc-A growth inhibition across 3D7/R539T/RKL-9 strains

   PMID:37088154

   Open questions at the time

   • Complementation shown in yeast rather than direct in-parasite loss-of-function
   • Roc-A binding mode to PfPHB2 not structurally defined
   • Not independently replicated
4. 2024 Medium

   Conditional depletion under mitochondrial stress revealed PfPHB2's anti-apoptotic role and functional coupling to the ClpQ protease, explaining why loss becomes lethal only when protein-quality-control is compromised.

   Evidence SLI C-terminal tagging, GlmS inducible knockdown with ROS, membrane potential, morphology, and proguanil susceptibility readouts in P. falciparum

   PMID:39245193

   Open questions at the time

   • Direct physical interaction between PfPHB2 and ClpQ not demonstrated
   • Substrates stabilized by the PHB2-ClpQ axis unidentified
   • Single lab, not independently replicated
5. 2024 Medium

   Detection of surface-exposed PfPHB2 binding host Hsp70A1A assigned a moonlighting invasion function beyond its mitochondrial role.

   Evidence GlmS knockdown of PfPHB2, siRNA depletion of host Hsp70A1A, recombinant RBC-binding, and antibody invasion-inhibition assays

   PMID:38812541

   Open questions at the time

   • Mechanism of PfPHB2 export/surface display from a mitochondrial protein unexplained
   • Downstream invasion signaling not characterized
   • Single lab, not independently replicated
6. 2025 Low

   Proximity labeling implicated host reticulocyte PHB2 as a co-receptor for the P. vivax ligand PvRBP1a, extending prohibitin's invasion relevance to the host side.

   Evidence TurboID proximity labeling with PvRBP1a-TurboID fusion, LC-MS membrane proteomics, and ELISA binding

   PMID:41078366

   Open questions at the time

   • Concerns host-cell PHB2, not the parasite PF3D7_1014700 protein
   • Co-receptor role novel and not independently validated
   • Functional invasion requirement not tested by loss-of-function

• How a mitochondrial prohibitin reaches the merozoite surface, and whether the PfPHB2-ClpQ and PfPHB2-Hsp70A1A functions are mechanistically linked, remains unresolved.
• Export/trafficking route to the merozoite surface unknown
• No structure of the PfPHB1-PfPHB2 complex
• Direct PfPHB2-ClpQ interaction unproven