Affinage · Plasmodium

RhopH2

PF3D7_0929400 · high molecular weight rhoptry protein 2

Annotated
2026-09-08
35 papers in source corpus 20 papers cited in narrative 20 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

RhopH2 (PF3D7_0929400) is an essential ~140 kDa Plasmodium falciparum rhoptry protein, synthesized during schizogony and localized to the apical rhoptry organelles of merozoites, that functions as an obligatory subunit of the high-molecular-mass RhopH complex driving nutrient acquisition at the infected erythrocyte membrane (PMID:3887156, PMID:11738712, PMID:28221136). It is encoded by a single-copy gene and, together with RhopH3, is shared across all RhopH complex variants, whereas the CLAG (RhopH1) subunit varies between complexes (PMID:12615335, PMID:15953647). RhopH2 is targeted to the rhoptry basal bulb via a signal within its N-terminal 24 amino acids that routes it through a Brefeldin A-sensitive secretory pathway (PMID:15049814, PMID:17175193, PMID:23539954). Structurally, RhopH2 assembles with CLAG3 and RhopH3 in a 1:1:1 soluble complex in which RhopH2 binds CLAG3 over a large interface but makes minimal direct contact with RhopH3, with the assembly stabilized by extensive intramolecular disulfide bonding and transmembrane helices shielded in the soluble state (PMID:33393463, PMID:34446549). Following merozoite invasion RhopH2 is discharged into the nascent parasitophorous vacuole, exported into the host cytoplasm via the PTEX translocon, and only then assembles with CLAG3 and inserts into the erythrocyte membrane to form the new permeability pathway (NPP/PSAC), a compartmentalized sequence that prevents premature channel assembly (PMID:32900800, PMID:33393463, PMID:35393572). RhopH2 is essential and cannot be knocked out; its conditional knockdown collapses the entire complex, abolishes channel-mediated solute uptake and de novo pyrimidine synthesis, and is lethal, while leaving erythrocyte invasion unaffected (PMID:28252383, PMID:28221136, PMID:32069335). Because RhopH2-dependent NPPs mediate Na+ influx, their loss protects infected cells from PfATP4-inhibitor-induced lysis, placing RhopH2 upstream of PfATP4-driven Na+ accumulation (PMID:31311978).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1985 High

    Establishing RhopH2 as a discrete rhoptry-resident protein defined it as an apical organellar factor rather than a surface antigen, framing its role in the invasion/post-invasion program.

    Evidence Monoclonal antibody affinity purification with immunofluorescence and immunoelectron microscopy in P. falciparum

    PMID:3887156

    Open questions at the time
    • Molecular function undefined at this stage
    • No partners identified
  2. 1993 Medium

    Detection of RhopH2 in a low-density pre-rhoptry vesicle before its appearance in mature rhoptries revealed a staggered biogenesis pathway for the protein.

    Evidence Sucrose-gradient subcellular fractionation and immunoelectron microscopy in P. falciparum

    PMID:8433718

    Open questions at the time
    • Trafficking machinery for vesicle maturation not defined
    • Timing relative to complex assembly unresolved
  3. 2003 High

    Identifying RhopH2 as a single-copy, schizont-transcribed gene conserved across species and defining the intact complex transfer to ring stages linked its biology to the post-invasion period.

    Evidence Gene cloning, cDNA screening and sequence analysis in P. falciparum and P. yoelii, with complex purification (also #2)

    PMID:11738712 PMID:12615335

    Open questions at the time
    • Function of the transferred complex not yet established
    • No mechanism for erythrocyte transfer
  4. 2005 Medium

    Defining complex composition showed RhopH2 (with RhopH3) is a constant subunit shared across variant complexes that each carry a single CLAG paralog, clarifying the combinatorial architecture.

    Evidence Immunoprecipitation, immunofluorescence and Western blotting with anti-CLAG antibodies in P. falciparum (with co-localization #5)

    PMID:15049814 PMID:15953647

    Open questions at the time
    • Functional consequence of CLAG variation not resolved
    • Stoichiometry not yet quantified
  5. 2013 Medium

    Mapping a rhoptry-targeting signal to the N-terminal 24 residues and demonstrating Brefeldin A sensitivity established that RhopH2 is sorted through the conventional secretory pathway.

    Evidence Transgenic GFP-chimera targeting assays and Brefeldin A treatment in P. falciparum (with earlier chimera mapping #7)

    PMID:17175193 PMID:23539954

    Open questions at the time
    • Specific sorting receptor/adaptor unidentified
    • How signal directs basal-bulb specificity unknown
  6. 2017 High

    Conditional knockdown and failed knockout established RhopH2 as essential and required for the whole complex, directly linking it to channel-mediated nutrient uptake, pyrimidine synthesis and parasite survival while excluding a direct invasion role.

    Evidence TetR-aptamer conditional knockdown, attempted knockout, solute-uptake assays, metabolomics and co-IP in P. falciparum (two concordant studies)

    PMID:28221136 PMID:28252383

    Open questions at the time
    • Molecular basis of channel formation not defined
    • Whether RhopH2 itself forms the pore unresolved
  7. 2019 Medium

    Placing RhopH2-dependent NPPs upstream of PfATP4-driven Na+ accumulation defined the transport pathway's position in the mechanism of a drug class.

    Evidence RhopH2 conditional knockdown with Na+ influx and PfATP4-inhibitor lysis assays in P. falciparum

    PMID:31311978

    Open questions at the time
    • Direct ion selectivity of RhopH2-containing channel not established
    • Epistasis based on functional readouts, not structure
  8. 2021 High

    Atomic-resolution cryo-EM of recombinant and endogenous complexes defined the 1:1:1 architecture with RhopH2 and RhopH3 bridged centrally by CLAG3, disulfide-stabilized and with membrane helices shielded, explaining why soluble trafficking precedes a conformational change for membrane insertion.

    Evidence Single-particle cryo-EM (2.9 Å) with mass spectrometry and PTEX conditional knockdown, plus independent endogenous-complex cryo-EM in P. falciparum

    PMID:33393463 PMID:34446549

    Open questions at the time
    • Membrane-inserted conformation not visualized
    • Trigger for the conformational change unknown
  9. 2022 High

    Demonstrating that RhopH2 is discharged into the parasitophorous vacuole and only assembles with CLAG3 after export established a compartmentalized, sequential assembly that prevents premature channel formation.

    Evidence Live, fixed and super-resolution microscopy with conditional knockdown and nutrient-uptake assays in P. falciparum (with FRET trafficking #13)

    PMID:32900800 PMID:35393572

    Open questions at the time
    • Signals gating assembly timing unknown
    • How RhopH2 crosses PTEX in an unfolded state unresolved
  10. 2026 Low

    A candidate stage-specific interaction between RhopH2 and the splicing factor PbSR1 in P. berghei raises the possibility of non-canonical RhopH2 associations, though its functional significance is undefined.

    Evidence Co-IP/MS and live-cell co-localization of dual-tagged transgenic P. berghei ANKA parasites

    PMID:41634752

    Open questions at the time
    • Functional significance of the interaction not established
    • Single co-IP/MS in a different species, not validated in P. falciparum
    • Cytoplasmic co-localization inconsistent with known rhoptry role

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the RhopH2-containing complex physically forms an ion/nutrient-conducting channel in the erythrocyte membrane, and what triggers the conformational change unshielding its transmembrane helices, remains unresolved.
  • No membrane-inserted structure
  • Pore-forming residues of RhopH2 unidentified
  • Trigger for soluble-to-membrane transition unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
CLAG3 (RHOPH1)CLAG9ERYTHROCYTE CYTOSKELETON AND EXPORTED HOST-REMODELING PROTEINSPBSR1 (P. BERGHEI, LOW CONFIDENCE)PTEX TRANSLOCON (EXPORT DEPENDENCE)RHOPH3
Complex memberships
New permeability pathway / PSAC channel at erythrocyte membraneRhopH complex (CLAG3/RhopH1–RhopH2–RhopH3, 1:1:1 stoichiometry)

Evidence

Reading pass · 20 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1985 RhopH2 is a ~140 kDa protein synthesized during schizogony that localizes to the rhoptries (apical organelles) of P. falciparum merozoites and is not expressed on the merozoite surface, as determined by monoclonal antibody affinity purification and immunolocalization. Monoclonal antibody affinity chromatography, immunofluorescence, immunoelectron microscopy Molecular and biochemical parasitology High 3887156
1993 During rhoptry biogenesis, RhopH2 (Rhop-H2) is detected in a low-density vesicle (pre-rhoptry compartment, peak density ~1.12 g/ml) at the four-nucleus schizont stage, before assembly into mature rhoptry vesicles of higher density (~1.16 g/ml) at the 16-nucleus stage, indicating a staggered assembly pathway. Subcellular fractionation by sucrose gradient, immunoelectron microscopy Molecular and biochemical parasitology Medium 8433718
2001 RhopH2 is a stoichiometric component of the high molecular mass RhopH complex (together with RhopH1/CLAG and RhopH3) in both P. falciparum and P. yoelii, as shown by monoclonal antibody purification of the intact complex. Monoclonal antibody purification, mass spectrometry, Edman degradation peptide sequencing Molecular and biochemical parasitology High 11738712
2003 RhopH2 is a single-copy gene product located on chromosome 9 of P. falciparum, transcribed during schizogony, with nine introns, and the encoded protein shares high amino acid sequence similarity with its P. yoelii ortholog; the intact RhopH complex (including RhopH2) is synthesized during schizogony and transferred to ring-stage parasites after erythrocyte invasion. Gene identification by peptide sequencing, oligonucleotide primer-based cloning, cDNA library screening with mAb 4E10, sequence analysis Molecular and biochemical parasitology High 12615335
2003 RhopH2 resides in detergent-resistant membrane (DRM) rafts within the rhoptry organelles, and upon erythrocyte invasion it is inserted into the newly formed parasitophorous vacuole membrane alongside rhoptry stomatin. Detergent-resistant membrane fractionation, immunofluorescence co-localization, immunoelectron microscopy The Journal of biological chemistry Medium 12968029
2004 RhopH2 co-localizes with Clag9 exclusively to the basal bulb region of rhoptries (not the apical ducts) in merozoites, and Clag9 is detected in the RhopH complex purified with anti-RhopH2 antibodies, confirming RhopH2 co-complex membership; after invasion, RhopH2 and Clag9 share identical ring-stage localization. Immunofluorescence co-localization, immunoelectron microscopy, immunoprecipitation with anti-RhopH2 antibody Molecular microbiology Medium 15049814
2005 The RhopH complex immunoprecipitated with anti-Clag9 antibody does not contain Clag2 or Clag3.1, indicating that individual RhopH complexes contain only single RhopH1/Clag gene products, while RhopH2 and RhopH3 (encoded by single-copy genes) are shared across all complex variants. Immunoprecipitation, immunofluorescence, Western blotting Molecular and biochemical parasitology Medium 15953647
2006 The N-terminal 24 amino acids of RhopH2 (including its signal peptide) are sufficient to target GFP to the rhoptries under the rhoph2 promoter in transgenic P. falciparum, indicating that a rhoptry-targeting signal resides within this short N-terminal sequence and is not mediated by timing of expression alone. Transgenic parasite expression of GFP chimeras, immunofluorescence localization in live and fixed parasites Parasitology international Medium 17175193
2008 After erythrocyte invasion, the RhopH complex (including RhopH2) is transferred not only to the parasitophorous vacuole membrane but also to defined domains of the red blood cell cytoplasm, with possible transient association with Maurer's clefts. Immunofluorescence, subcellular fractionation, immuno-electron microscopy Molecular and biochemical parasitology Medium 18508137
2013 An RhopH2 signal peptide–GFP chimera (containing the RhopH2 signal peptide plus the downstream five amino acids) is trafficked to the rhoptries via a Brefeldin A-sensitive pathway, indicating that rhoptry targeting of RhopH2 passes through the conventional secretory pathway and that the five residues downstream of signal cleavage contribute to the sorting signal. Brefeldin A treatment of transgenic parasites expressing RhopH2-GFP chimera, live-cell fluorescence imaging Folia parasitologica Medium 23539954
2017 Conditional knockdown of RhopH2 in P. falciparum disrupts the entire RhopH complex, interfering with organellar targeting and subsequent trafficking of both RhopH2 and other complex members; RhopH2 knockdown reduces uptake of solutes that use new permeability pathways (NPPs), depletes essential vitamins and cofactors, decreases de novo pyrimidine synthesis, and impairs parasite growth and replication. RhopH2 was shown by co-immunoprecipitation to interact with RhopH1, RhopH3, the erythrocyte cytoskeleton, and exported host-cell remodeling proteins. Conditional knockdown (TetR-aptamer system), solute uptake assays, metabolomics, co-immunoprecipitation, growth assays eLife High 28252383
2017 RhopH2 is essential in P. falciparum: the rhoph2 gene cannot be knocked out; conditional knockdown of RhopH2 disrupts the entire RhopH complex (including organellar targeting), and the complex is required for channel-mediated nutrient uptake at the erythrocyte membrane. RhopH2 does not contribute directly to erythrocyte invasion (invasion was not affected upon RhopH2 knockdown). After export via the PTEX translocon, RhopH2 becomes part of a nutrient channel at the host membrane. Conditional knockdown, attempted gene knockout, PSAC transport assays, trafficking assays eLife High 28221136
2019 Knockdown of RhopH2 expression reduces influx of Na+ into infected erythrocytes through new permeability pathways (NPPs), thereby protecting infected erythrocytes from lysis induced by PfATP4 inhibitors; this places RhopH2-dependent NPPs upstream of PfATP4-driven Na+ accumulation in the mechanism of action of PfATP4 inhibitors. RhopH2 conditional knockdown, Na+ influx assays, infected erythrocyte lysis assays with PfATP4 inhibitor MB14 Scientific reports Medium 31311978
2020 Live-cell FRET between CLAG3-mCerulean and RhopH2-mVenus demonstrates that RhopH2 and CLAG3 remain tightly associated throughout their trafficking: from synthesis and packaging in rhoptries, through deposition into the parasitophorous vacuole after invasion, to export and insertion at the erythrocyte membrane. Stoichiometric increases in exported RhopH2 and CLAG3 protein correlate with proportional increases in PSAC functional copy number. FRET live-cell imaging, gene editing (fluorescent tagging), whole-cell patch-clamp electrophysiology, fluorescence intensity quantification mBio High 32900800
2020 RhopH2 cannot be disrupted (complete knockout is not viable) under conditions where nutrient uptake is abolished, in contrast to CLAG3 which can be fully knocked out with only partial loss of transport. This places RhopH2 as essential for nutrient transport activity in a manner that cannot be compensated by CLAG paralog oligomerization. Attempted gene knockout by CRISPR/selection, PSAC transport assays, conditional knockdown PLoS pathogens Medium 32069335
2021 The soluble trafficking RhopH complex is assembled with 1:1:1 stoichiometry of CLAG3, RhopH2, and RhopH3. A 2.9 Å cryo-EM structure shows that RhopH2 and RhopH3 interact with CLAG3 over large surface areas but make minimal direct contacts with each other; CLAG3 is positioned centrally between them. The complex is stabilized by extensive intramolecular disulfide bonding and predicted transmembrane helices are shielded in the soluble form. Export to the erythrocyte membrane requires the PTEX translocon. Single-particle cryo-electron microscopy (2.9 Å), mass spectrometry, stoichiometry analysis, PTEX translocon conditional knockdown eLife High 33393463
2021 Cryo-EM structure of the native, endogenous RhopH complex purified directly from parasite lysates shows RhopH2 bound to CLAG3.1 with a substantial interface; RhopH2 and RhopH3 share large binding surfaces with CLAG3.1 but make minimal contact with each other. The complex contains 13 intramolecular disulfide bonds overall, and the putative CLAG3.1 transmembrane helix is buried in a helical bundle, suggesting a large conformational change is required for membrane insertion. Cryo-electron microscopy (endogenous complex), mass spectrometry, cryoID program for subunit identification Proceedings of the National Academy of Sciences of the United States of America High 34446549
2021 Five exported proteins (identified by reciprocal immunoprecipitation with mass spectrometry) interact with all members of the RhopH complex including RhopH2 in the infected erythrocyte; these interactions suggest a cytoskeletal complex and a Maurer's clefts/J-dot complex associated with the RhopH complex, providing candidate trafficking intermediates. Knockdown of these 13 candidate interactors individually had no effect on sorbitol NPP uptake, indicating they are not individually required for NPP function. Reciprocal immunoprecipitation, mass spectrometry-based proteomics, NPP activity assay (sorbitol uptake), conditional knockdown Cellular microbiology Medium 33774908
2022 After merozoite invasion, RhopH2 is released into the nascent parasitophorous vacuole (not directly into the host cell cytoplasm, unlike CLAG3). Export of RhopH2 from the parasitophorous vacuole into the infected erythrocyte cytoplasm enables assembly of the Clag3/RhopH2/RhopH3 complex, which is then incorporated into the host cell membrane concomitant with activation of nutrient uptake. The full RhopH complex is not pre-assembled during merozoite invasion; compartmentalization prevents premature channel assembly. Fluorescence microscopy (live and fixed), conditional knockdown, super-resolution microscopy, nutrient uptake assays Communications biology High 35393572
2026 In P. berghei, PbSR1 (a serine/arginine-rich splicing factor) co-immunoprecipitates with RhopH2, and live-cell imaging shows cytoplasmic co-localization of PbSR1 and RhopH2 in trophozoites and gametocytes but not in mature schizonts or merozoites. Immunoprecipitation coupled to mass spectrometry, live-cell fluorescence imaging of dual-tagged transgenic parasites, Western blot Malaria journal Low 41634752

Source papers

Stage 0 corpus · 35 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1985 Isolation of a Plasmodium falciparum rhoptry protein. Molecular and biochemical parasitology 103 3887156
2017 Plasmodium falciparum parasites deploy RhopH2 into the host erythrocyte to obtain nutrients, grow and replicate. eLife 92 28252383
2017 An essential dual-function complex mediates erythrocyte invasion and channel-mediated nutrient uptake in malaria parasites. eLife 90 28221136
2003 Identification of a stomatin orthologue in vacuoles induced in human erythrocytes by malaria parasites. A role for microbial raft proteins in apicomplexan vacuole biogenesis. The Journal of biological chemistry 80 12968029
2001 The high molecular mass rhoptry protein, RhopH1, is encoded by members of the clag multigene family in Plasmodium falciparum and Plasmodium yoelii. Molecular and biochemical parasitology 72 11738712
2004 The Plasmodium falciparum clag9 gene encodes a rhoptry protein that is transferred to the host erythrocyte upon invasion. Molecular microbiology 70 15049814
2005 Apical expression of three RhopH1/Clag proteins as components of the Plasmodium falciparum RhopH complex. Molecular and biochemical parasitology 68 15953647
2008 The RhopH complex is transferred to the host cell cytoplasm following red blood cell invasion by Plasmodium falciparum. Molecular and biochemical parasitology 57 18508137
2011 Functional analysis of epigenetic regulation of tandem RhopH1/clag genes reveals a role in Plasmodium falciparum growth. Molecular microbiology 46 21320181
2007 Diversity and evolution of the rhoph1/clag multigene family of Plasmodium falciparum. Molecular and biochemical parasitology 46 18155305
2021 Malaria parasites use a soluble RhopH complex for erythrocyte invasion and an integral form for nutrient uptake. eLife 44 33393463
2003 Characterisation of the rhoph2 gene of Plasmodium falciparum and Plasmodium yoelii. Molecular and biochemical parasitology 41 12615335
1993 Biogenesis of rhoptry organelles in Plasmodium falciparum. Molecular and biochemical parasitology 40 8433718
2006 Comparative transcriptomal analysis of isogenic Plasmodium falciparum clones of distinct antigenic and adhesive phenotypes. Molecular and biochemical parasitology 35 17196675
2020 Complex nutrient channel phenotypes despite Mendelian inheritance in a Plasmodium falciparum genetic cross. PLoS pathogens 33 32069335
2002 Plasmodium falciparum MAEBL is a unique member of the ebl family. Molecular and biochemical parasitology 32 12076768
1994 Analysis of the high molecular weight rhoptry complex of Plasmodium falciparum using monoclonal antibodies. Parasitology 29 7517517
2021 Native structure of the RhopH complex, a key determinant of malaria parasite nutrient acquisition. Proceedings of the National Academy of Sciences of the United States of America 26 34446549
2021 Characterisation of complexes formed by parasite proteins exported into the host cell compartment of Plasmodium falciparum infected red blood cells. Cellular microbiology 23 33774908
2019 A 4-cyano-3-methylisoquinoline inhibitor of Plasmodium falciparum growth targets the sodium efflux pump PfATP4. Scientific reports 23 31311978
2006 The Plasmodium falciparum RhopH2 promoter and first 24 amino acids are sufficient to target proteins to the rhoptries. Parasitology international 22 17175193
2020 Live-Cell FRET Reveals that Malaria Nutrient Channel Proteins CLAG3 and RhopH2 Remain Associated throughout Their Tortuous Trafficking. mBio 19 32900800
2022 RhopH2 and RhopH3 export enables assembly of the RhopH complex on P. falciparum-infected erythrocyte membranes. Communications biology 17 35393572
2012 Identification and characterization of the Plasmodium falciparum RhopH2 ortholog in Plasmodium vivax. Parasitology research 9 23097184
2021 Identification of a Novel RAMA/RON3 Rhoptry Protein Complex in Plasmodium falciparum Merozoites. Frontiers in cellular and infection microbiology 8 33537242
2020 Plasmodium falciparum Clag9-Associated PfRhopH Complex Is Involved in Merozoite Binding to Human Erythrocytes. Infection and immunity 8 31712270
2022 Identification, Mapping, and Genetic Diversity of Novel Conserved Cross-Species Epitopes of RhopH2 in Plasmodium knowlesi With Plasmodium vivax. Frontiers in cellular and infection microbiology 6 35096656
2019 The persistence of naturally acquired antibodies and memory B cells specific to rhoptry proteins of Plasmodium vivax in patients from areas of low malaria transmission. Malaria journal 6 31783870
2016 Malaria Parasite CLAG3, a Protein Linked to Nutrient Channels, Participates in High Molecular Weight Membrane-Associated Complexes in the Infected Erythrocyte. PloS one 4 27299521
2026 Evolutionary rate covariation across malaria parasite species enables inference of protein interactions. bioRxiv : the preprint server for biology 2 41659435
2013 Trafficking of Plasmodium falciparum chimeric rhoptry protein with Brefeldin A. Folia parasitologica 2 23539954
2009 [Transcription profile of PfRON4 gene in Plasmodium falciparum erythrocytic stage]. Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 2 19852359
2026 Identification of serine/arginine-rich splicing factor 1-interacting proteins in Plasmodium berghei. Malaria journal 0 41634752
2026 A CRISPR-Based Mutagenesis Strategy for Examining CLAG3 Helix 44 Contribution to Malaria Parasite Nutrient Uptake Channels. Genes 0 42074580
2026 Evolutionary Rate Covariation Across Malaria Parasite Species Enables Inference of Protein Interactions. Genome biology and evolution 0 42664386