Affinage · Toxoplasma gondii

RON5

rhoptry neck protein RON5 · UniProt S8ERS3

Annotated
2026-09-08
9 papers in source corpus 6 papers cited in narrative 10 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

RON5 is a rhoptry neck protein of Toxoplasma gondii that functions as a core structural component of the moving junction (MJ), the ring-shaped interface through which the parasite penetrates host cells (PMID:19247437). Within the parasite it assembles into a preformed complex with the other RON proteins (RON2, RON4, RON8) prior to secretion, and this complex is discharged and targeted to the cytoplasmic face of the host plasma membrane during invasion (PMID:19247437, PMID:19134112). RON5 acts as an organizational hub for this complex: its loss triggers complete degradation of RON2 and mistargeting of RON4 within the secretory pathway, with a portion of its C-terminal domain being specifically required for RON2 stability and invasion function (PMID:24651769). Functionally, RON5 is essential for host cell penetration and for secretion of rhoptry bulb contents (evacuole formation), but is dispensable for parasite egress (PMID:24651769). Together with RON2 and RON4, RON5 actively recruits host proteins CIN85, CD2AP, and the ESCRT-I components ALIX and TSG101 to the MJ by mimicking conserved host binding interfaces, coupling junction assembly to host machinery during invasion (PMID:28848228).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2008 Medium

    Establishing that RON5 physically belongs to the MJ RON machinery was the first step in defining its role, showing it is part of a preformed intracellular complex rather than an isolated factor.

    Evidence Co-immunoprecipitation of RON5 with RON8, RON2, and RON4 from extracellular parasites

    PMID:19134112

    Open questions at the time
    • Does not establish stoichiometry or direct binding partners within the complex
    • Does not address function during invasion
  2. 2009 High

    Localizing RON5 to the cytoplasmic face of the host plasma membrane during invasion demonstrated it is a bona fide MJ component secreted into the host interface, not merely a parasite-resident protein.

    Evidence Differential permeabilization with RON-specific antibodies, immunoprecipitation, and metabolic labeling

    PMID:19247437

    Open questions at the time
    • Does not resolve how RON5 is anchored at the host membrane
    • Functional requirement not yet tested genetically
  3. 2014 High

    Conditional knockdown established RON5 as an organizational keystone of the MJ complex and defined its functional requirements, resolving whether it is structural or merely associated.

    Evidence Tetracycline-regulatable knockdown with Western blot, immunofluorescence, invasion, evacuole, and egress assays; complementation with domain mutagenesis

    PMID:24651769

    Open questions at the time
    • Mechanism by which RON5 stabilizes RON2 within the secretory pathway is not defined
    • Molecular function of the critical C-terminal region is unresolved
    • Reason egress is spared while invasion fails is not mechanistically explained
  4. 2017 High

    Mapping host-protein recruitment showed the RON5/RON2/RON4 complex subverts host CIN85, CD2AP, and ESCRT-I components by mimicking conserved binding interfaces, connecting MJ assembly to host cellular machinery.

    Evidence Co-immunoprecipitation, interaction mapping, and parasite mutant analysis in culture and in vivo

    PMID:28848228

    Open questions at the time
    • The specific contribution of RON5 versus RON2/RON4 to each host interaction is not isolated
    • Downstream consequences of host protein recruitment for invasion are not fully defined
  5. 2017 Medium

    Reciprocal dependency and complex-boundary experiments refined the interdependence of RON components, showing RON4 supports RON5 N-terminal stability while RON4L1 traffics independently of RON5.

    Evidence CRISPR-Cas9 knockout and Western blot for RON4 dependency; knockout lines with invasion-stage immunofluorescence for RON4L1 trafficking

    PMID:28662729 PMID:29263399

    Open questions at the time
    • RON4-mediated stabilization of RON5 shown only at protein level in RH strain
    • Whether RON4L1 forms a distinct MJ sub-complex is not directly demonstrated

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural basis of RON5-mediated RON2 stabilization and the molecular identity of its critical C-terminal function within the secretory pathway remain unresolved.
  • No structural model of the RON5-RON2 interaction
  • Mechanism of C-terminal domain action on RON2 stability undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
HOST ALIXHOST CD2APHOST CIN85HOST TSG101RON2RON4RON8
Complex memberships
Moving junction RON complex (RON2, RON4, RON5, RON8)

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2009 RON5 is a component of the moving junction (MJ) complex, localizing to the cytoplasmic face of the host plasma membrane during invasion, as demonstrated by differential permeabilization and loading of RON-specific antibodies into the host cell. Differential permeabilization, immunoprecipitation, metabolic labeling PLoS pathogens High 19247437
2008 RON5 is conserved in Plasmodium and co-immunoprecipitates with RON8 and other known MJ proteins (RON2, RON4) from extracellular parasites, indicating RON5 is part of a preformed complex within the parasite prior to secretion. Co-immunoprecipitation Cellular microbiology Medium 19134112
2014 Conditional knockdown of RON5 results in complete degradation of RON2 and mistargeting of RON4 within the parasite secretory pathway, demonstrating that RON5 is essential for organization and stability of the MJ RON complex. Conditional knockdown (tetracycline-regulatable), Western blot, immunofluorescence PLoS pathogens High 24651769
2014 Loss of RON5 by conditional knockdown renders parasites unable to invade host cells, providing the first genetic demonstration that RON5 is required for host cell penetration. Conditional knockdown, invasion assay PLoS pathogens High 24651769
2014 Parasites lacking RON5 fail to form evacuoles, demonstrating that an intact MJ complex (dependent on RON5) is a prerequisite for secretion of rhoptry bulb contents. Conditional knockdown, evacuole formation assay PLoS pathogens High 24651769
2014 Disruption of the MJ complex by RON5 depletion does not impact parasite egress, indicating RON5 and the MJ complex are not required for egress. Conditional knockdown, egress assay PLoS pathogens Medium 24651769
2014 Functional complementation of the RON5 conditional mutant revealed that proteolytic separation of RON5 N- and C-terminal fragments is dispensable, but a portion of the C-terminal domain is critical for RON2 stability and invasion function. Functional complementation, mutagenesis, invasion assay, Western blot PLoS pathogens High 24651769
2017 RON5 cooperates with RON2 and RON4 to actively recruit host proteins CIN85, CD2AP, and ESCRT-I components ALIX and TSG101 to the moving junction during invasion, with the parasite mimicking conserved host binding interfaces. Co-immunoprecipitation, interaction mapping, parasite mutant analysis (invasion and virulence assays) Nature microbiology High 28848228
2017 RON4 knockout decreases the expression of the endogenous N-terminal fragment of RON5, indicating that RON4 contributes to the stability of RON5 within the MJ complex. CRISPR-Cas9 knockout, Western blot Parasitology Medium 28662729
2017 RON4L1 traffic to the MJ is not affected in the absence of RON2, RON4, or RON5, suggesting that RON4L1 is part of an independent MJ sub-complex rather than depending on these RON proteins for its targeting. Knockout cell line generation, immunofluorescence localization during invasion Scientific reports Medium 29263399

Source papers

Stage 0 corpus · 9 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2009 Export of a Toxoplasma gondii rhoptry neck protein complex at the host cell membrane to form the moving junction during invasion. PLoS pathogens 238 19247437
2008 Novel components of the Apicomplexan moving junction reveal conserved and coccidia-restricted elements. Cellular microbiology 92 19134112
2017 Efficient invasion by Toxoplasma depends on the subversion of host protein networks. Nature microbiology 50 28848228
2014 RON5 is critical for organization and function of the Toxoplasma moving junction complex. PLoS pathogens 47 24651769
2017 RON4L1 is a new member of the moving junction complex in Toxoplasma gondii. Scientific reports 16 29263399
2016 Protective efficacy of pVAX-RON5p against acute and chronic infections of Toxoplasma gondii in BALB/c mice. Experimental parasitology 10 26821295
2017 The moving junction protein RON4, although not critical, facilitates host cell invasion and stabilizes MJ members. Parasitology 6 28662729
2018 Deciphering ophthalmic adaptive inhibitors targeting RON4 of Toxoplasma gondii: An integrative in silico approach. Life sciences 5 30326220
2025 In silico evaluation of Toxoplasma gondii rhoptry neck proteins (TgRONs) for potential immunogenic epitopes. EXCLI journal 1 40881926