{"gene":"PF3D7_0424400","run_date":"2026-09-07T10:55:51","timeline":{"discoveries":[{"year":2005,"finding":"SURF4.2 (SURFIN4.2) protein was identified on the surface of live P. falciparum-infected erythrocytes (IEs) by mass spectrometric analysis of trypsin-cleaved peptides, and was found co-transported with PfEMP1 and RIFIN to the IE surface. It also accumulated in the parasitophorous vacuole and was present as an amorphous cap at the apex of released merozoites.","method":"Mass spectrometric analysis of surface-trypsinized peptides from live IEs; immunofluorescence assay; co-localization with PfEMP1 and RIFIN","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct surface proteomics identification plus IFA co-localization, single lab, two orthogonal methods","pmids":["15939796"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2007,"finding":"SURF4.2 (SURFIN4.2) was detected in Maurer's clefts of P. falciparum-infected erythrocytes, alongside PfEMP1 and RIFIN, by immunofluorescence assay combined with Giemsa staining, placing it in this trafficking compartment.","method":"Indirect immunofluorescence assay combined with Giemsa staining and transmission electron microscopy","journal":"The American journal of tropical medicine and hygiene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single IFA method, no functional consequence tested","pmids":["17255224"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"SURF4.2 trafficking to the infected RBC and Maurer's clefts is PEXEL-independent: the transmembrane (TM) region is necessary and sufficient for trafficking, whereas two PEXEL-like sequences, the N-terminal cysteine-rich domain, the variable region, and the WR domain are not required for this trafficking step. A mini-SURF4.2 containing 50 amino acids upstream of TM, the TM itself, and part of the cytoplasmic region was sufficient for localization to the iRBC and Maurer's clefts.","method":"Transgenic parasite lines expressing GFP-fused SURFIN4.2 deletion/replacement constructs; immunofluorescence assay; Western blotting with Triton X-100 fractionation","journal":"Parasitology international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic deletion mutagenesis in transgenic parasites with multiple orthogonal readouts, single lab","pmids":["21616162"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2011,"finding":"The cytoplasmic WR domain of SURF4.2 is associated with Triton X-100 insolubility: a recombinant SURF4.2 containing the WR domain was more abundantly detected in the Triton X-100-insoluble fraction compared to one without the WR domain, suggesting the WR domain influences membrane skeleton association or detergent-resistant complex formation.","method":"Western blotting of Triton X-100 fractionated transgenic parasite lysates","journal":"Parasitology international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single biochemical fractionation, single lab, no direct functional consequence demonstrated","pmids":["21616162"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2015,"finding":"The intracellular region of SURF4.2 containing the tryptophan-rich (WR) domain is required for transport from Maurer's clefts to the iRBC surface: transgenic parasites expressing SURF4.2 without the intracellular WR-containing region were exported to Maurer's clefts but were not efficiently cleaved by surface proteinase K treatment, whereas those retaining the intracellular region were surface-exposed.","method":"Transgenic parasite lines expressing modified SURFIN4.2 with/without intracellular region; proteinase K surface treatment of iRBC; immunofluorescence assay","journal":"Tropical medicine and health","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional domain dissection using transgenic parasites with surface accessibility assay, single lab, two orthogonal readouts","pmids":["26865830"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2017,"finding":"The second tryptophan-rich domain (WRD2) of SURF4.2 directly binds the red blood cell membrane skeleton: recombinant WRD2 bound inside-out vesicles (IOVs) of RBCs with Kd in the range of 0.26–0.68 µM, F-actin with Kd = 5.16 µM, and spectrin with Kd = 0.51 µM.","method":"In vitro binding assay with inside-out vesicles; actin spin-down assay; ELISA-based spectrin binding assay; recombinant protein expression; transgenic parasite fluorescence microscopy","journal":"Malaria journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution binding assays with quantified affinities using three orthogonal methods (IOV binding, actin co-sedimentation, ELISA), single lab","pmids":["28320404"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2018,"finding":"SURF4.2 is present in the neck of the rhoptries of P. falciparum merozoites, is secreted into the parasitophorous vacuole, and is shed into culture supernatant upon schizont rupture. SURF4.2 forms a protein complex (named SURGE) with the rhoptry neck protein RON4 and the Glutamate Rich Protein GLURP, as shown by immunoprecipitation followed by mass spectrometry. The N-terminal cysteine-rich domain (CRD) of SURF4.2 mediates binding to the RBC membrane. Polyclonal antibodies against the extracellular domain (including CRD) of SURF4.2 partially inhibit merozoite invasion.","method":"Immunoprecipitation followed by mass spectrometry (co-IP/MS); antibody localization by immunofluorescence and immunoelectron microscopy; invasion inhibition assay with polyclonal antibodies","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP/MS identification of complex plus functional invasion inhibition assay, single lab, multiple orthogonal methods","pmids":["30092030"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2019,"finding":"N-terminally Myc-tagged mini-SURF4.2 (containing the N-terminal region, TM region, and cytoplasmic region) was detected at Maurer's clefts by anti-Myc antibody staining, indicating that the N-terminal sequence of SURF4.2 is not cleaved during export and that elements required for export to Maurer's clefts are conserved between SURFIN4.1 and SURFIN4.2.","method":"Transgenic parasite lines expressing Myc-tagged mini-SURFIN4.2; immunofluorescence assay with anti-Myc antibody","journal":"Parasitology international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single IFA readout, single lab, finding is secondary to main SURFIN4.1 study","pmids":["31028841"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2018,"finding":"Naturally acquired antibodies from children with malaria react with SURF4.2 at the parasitized RBC surface, and data indicate SURF4.2 may have a function during rosette formation, though this was not formally validated in the study.","method":"Serological profiling with peptide arrays; assessment of rosetting rate and surface reactivity using patient sera","journal":"Scientific reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect serological evidence of surface exposure; rosette formation role explicitly noted as unvalidated","pmids":["29459776"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"FCR3S1.2"}]}],"current_model":"SURF4.2 (PF3D7_0424400) is a type I transmembrane protein exported from the parasite to Maurer's clefts via a PEXEL-independent, transmembrane-domain-dependent mechanism, and further transported to the infected erythrocyte surface via its cytoplasmic tryptophan-rich (WR) domain; the WR domain directly binds RBC membrane skeletal components (spectrin and F-actin), and in merozoites SURF4.2 localizes to the rhoptry neck where it forms the SURGE complex with RON4 and GLURP, with its extracellular cysteine-rich domain mediating RBC membrane binding and contributing to merozoite invasion."},"narrative":{"mechanistic_narrative":"SURF4.2 (PF3D7_0424400) is a Plasmodium falciparum type I transmembrane protein that operates at two stages of the intraerythrocytic cycle: it is exported to the surface of infected erythrocytes during blood-stage growth and relocalizes to the merozoite apex for invasion [PMID:15939796]. During export, SURF4.2 traffics through Maurer's clefts to the infected-RBC surface by a PEXEL-independent route in which the transmembrane region is necessary and sufficient for delivery to the clefts, while the N-terminal sequence remains uncleaved [PMID:21616162, PMID:17255224]. Onward transport from Maurer's clefts to the erythrocyte surface then depends on the cytoplasmic tryptophan-rich (WR) domain [PMID:26865830], which drives detergent-resistant membrane-skeleton association [PMID:21616162]; the second WR domain (WRD2) binds the RBC membrane skeleton directly, engaging inside-out vesicles, F-actin and spectrin with sub-micromolar to low-micromolar affinity [PMID:28320404]. In merozoites SURF4.2 localizes to the rhoptry neck and is secreted into the parasitophorous vacuole, where it assembles into the SURGE complex with the rhoptry neck protein RON4 and GLURP; its N-terminal extracellular cysteine-rich domain mediates RBC membrane binding, and antibodies against the extracellular domain partially inhibit merozoite invasion [PMID:30092030]. Whether SURF4.2 has a role in rosette formation is a surface-antibody-based observation that was not functionally validated [PMID:29459776].","teleology":[{"year":2005,"claim":"Establishing that SURF4.2 reaches the infected-erythrocyte surface answered whether this protein is a parasite-derived surface antigen co-trafficked with known virulence proteins.","evidence":"Surface trypsinization plus mass spectrometry and IFA co-localization with PfEMP1 and RIFIN on live infected erythrocytes","pmids":["15939796"],"confidence":"Medium","gaps":["Trafficking route and domain requirements not defined","Functional role at the surface not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2007,"claim":"Detecting SURF4.2 in Maurer's clefts identified the intermediate trafficking compartment on the path to the erythrocyte surface.","evidence":"Indirect immunofluorescence with Giemsa staining and transmission electron microscopy on infected erythrocytes","pmids":["17255224"],"confidence":"Low","gaps":["Single IFA method, no functional consequence tested","Does not resolve how the protein enters or exits the clefts"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Domain-mapping resolved that SURF4.2 export is PEXEL-independent and driven by its transmembrane region, distinguishing it from canonical PEXEL-motif exported proteins.","evidence":"GFP-fusion deletion/replacement constructs in transgenic parasites with IFA and Triton X-100 fractionation Western blotting","pmids":["21616162"],"confidence":"Medium","gaps":["Mechanism recognizing the TM region for export not identified","Onward step to the surface not addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2011,"claim":"Biochemical fractionation linked the cytoplasmic WR domain to detergent-resistant/membrane-skeleton association, hinting at how SURF4.2 anchors at the erythrocyte cortex.","evidence":"Triton X-100 fractionation and Western blotting of recombinant SURF4.2 constructs with and without the WR domain","pmids":["21616162"],"confidence":"Low","gaps":["Single biochemical fractionation, no direct binding partner shown","Functional consequence not demonstrated"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2015,"claim":"Functional dissection showed the cytoplasmic WR-containing region is required for the final step of transport from Maurer's clefts to the iRBC surface, defining a two-stage export mechanism.","evidence":"Transgenic parasites with/without the intracellular region, proteinase K surface accessibility assay and IFA","pmids":["26865830"],"confidence":"Medium","gaps":["Molecular partners at the surface delivery step not identified","Does not quantify surface abundance or virulence impact"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2017,"claim":"In vitro binding assays established a direct molecular interaction between SURF4.2 and the RBC membrane skeleton, providing the biochemical basis for its cortical anchoring.","evidence":"Recombinant WRD2 binding to inside-out vesicles, F-actin co-sedimentation, and ELISA-based spectrin binding with quantified affinities","pmids":["28320404"],"confidence":"High","gaps":["Binding not demonstrated in the native cellular context","Physiological consequence of skeleton binding for the host cell not established"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2018,"claim":"Identifying rhoptry-neck localization and the SURGE complex extended SURF4.2's role beyond surface display to invasion, defining its partners and an invasion-relevant binding domain.","evidence":"Reciprocal co-IP/MS identifying RON4 and GLURP, immuno-EM localization, and antibody-based invasion inhibition assays","pmids":["30092030"],"confidence":"Medium","gaps":["Stoichiometry and assembly order of the SURGE complex unknown","Erythrocyte receptor for the CRD not identified","Only partial invasion inhibition observed"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2018,"claim":"Serological profiling confirmed SURF4.2 is an immune target at the infected-cell surface and raised the possibility of a rosetting role.","evidence":"Peptide-array serology with patient sera and rosetting-rate assessment","pmids":["29459776"],"confidence":"Low","gaps":["Rosette role explicitly not functionally validated","Indirect serological inference of surface exposure"],"attribution":[{"species":"Plasmodium falciparum","strain":"FCR3S1.2"}]},{"year":2019,"claim":"Tagged mini-SURF4.2 confirmed the N-terminus is not cleaved during export and that Maurer's-cleft targeting elements are shared with the paralog SURFIN4.1.","evidence":"Myc-tagged mini-SURF4.2 transgenic parasites with anti-Myc IFA","pmids":["31028841"],"confidence":"Low","gaps":["Single IFA readout secondary to a SURFIN4.1 study","Does not identify the export receptor for the shared signal"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":null,"claim":"The erythrocyte surface receptor engaged by the SURF4.2 extracellular cysteine-rich domain during invasion, and the causal contribution of its membrane-skeleton binding to host-cell remodeling or rosetting, remain undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No identified host receptor for the CRD","SURGE complex assembly mechanism unresolved","Rosetting role not functionally tested"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["SURGE complex (SURF4.2 with RON4 and GLURP) [#6]"],"partners":["RON4 (RHOPTRY NECK PROTEIN) [#6]","GLURP (GLUTAMATE-RICH PROTEIN) [#6]","RBC SPECTRIN [#5]","RBC F-ACTIN [#5]","RBC INSIDE-OUT MEMBRANE VESICLES [#5]"],"other_free_text":["Type I transmembrane protein exported via a PEXEL-independent, transmembrane-domain-dependent route [#2].","Co-transported to the infected-erythrocyte surface with PfEMP1 and RIFIN [#0].","Cytoplasmic WR domain required for the Maurer's-cleft-to-surface transport step and confers Triton X-100 insolubility [#3, #4].","N-terminal extracellular cysteine-rich domain mediates RBC membrane binding and contributes to merozoite invasion [#6].","Target of naturally acquired antibodies at the infected-RBC surface, with an unvalidated possible role in rosette formation [#8].","Export/Maurer's-cleft targeting elements shared with the paralog SURFIN4.1 [#7]."]}},"prefetch_data":{},"corpus_meta":[{"pmid":"18614010","id":"PMC_18614010","title":"Exported proteins required for virulence and rigidity of Plasmodium falciparum-infected human 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PfEMP1 and RIFIN to the IE surface. It also accumulated in the parasitophorous vacuole and was present as an amorphous cap at the apex of released merozoites.\",\n      \"method\": \"Mass spectrometric analysis of surface-trypsinized peptides from live IEs; immunofluorescence assay; co-localization with PfEMP1 and RIFIN\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct surface proteomics identification plus IFA co-localization, single lab, two orthogonal methods\",\n      \"pmids\": [\"15939796\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SURF4.2 (SURFIN4.2) was detected in Maurer's clefts of P. falciparum-infected erythrocytes, alongside PfEMP1 and RIFIN, by immunofluorescence assay combined with Giemsa staining, placing it in this trafficking compartment.\",\n      \"method\": \"Indirect immunofluorescence assay combined with Giemsa staining and transmission electron microscopy\",\n      \"journal\": \"The American journal of tropical medicine and hygiene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single IFA method, no functional consequence tested\",\n      \"pmids\": [\"17255224\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SURF4.2 trafficking to the infected RBC and Maurer's clefts is PEXEL-independent: the transmembrane (TM) region is necessary and sufficient for trafficking, whereas two PEXEL-like sequences, the N-terminal cysteine-rich domain, the variable region, and the WR domain are not required for this trafficking step. A mini-SURF4.2 containing 50 amino acids upstream of TM, the TM itself, and part of the cytoplasmic region was sufficient for localization to the iRBC and Maurer's clefts.\",\n      \"method\": \"Transgenic parasite lines expressing GFP-fused SURFIN4.2 deletion/replacement constructs; immunofluorescence assay; Western blotting with Triton X-100 fractionation\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic deletion mutagenesis in transgenic parasites with multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"21616162\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The cytoplasmic WR domain of SURF4.2 is associated with Triton X-100 insolubility: a recombinant SURF4.2 containing the WR domain was more abundantly detected in the Triton X-100-insoluble fraction compared to one without the WR domain, suggesting the WR domain influences membrane skeleton association or detergent-resistant complex formation.\",\n      \"method\": \"Western blotting of Triton X-100 fractionated transgenic parasite lysates\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single biochemical fractionation, single lab, no direct functional consequence demonstrated\",\n      \"pmids\": [\"21616162\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The intracellular region of SURF4.2 containing the tryptophan-rich (WR) domain is required for transport from Maurer's clefts to the iRBC surface: transgenic parasites expressing SURF4.2 without the intracellular WR-containing region were exported to Maurer's clefts but were not efficiently cleaved by surface proteinase K treatment, whereas those retaining the intracellular region were surface-exposed.\",\n      \"method\": \"Transgenic parasite lines expressing modified SURFIN4.2 with/without intracellular region; proteinase K surface treatment of iRBC; immunofluorescence assay\",\n      \"journal\": \"Tropical medicine and health\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional domain dissection using transgenic parasites with surface accessibility assay, single lab, two orthogonal readouts\",\n      \"pmids\": [\"26865830\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The second tryptophan-rich domain (WRD2) of SURF4.2 directly binds the red blood cell membrane skeleton: recombinant WRD2 bound inside-out vesicles (IOVs) of RBCs with Kd in the range of 0.26–0.68 µM, F-actin with Kd = 5.16 µM, and spectrin with Kd = 0.51 µM.\",\n      \"method\": \"In vitro binding assay with inside-out vesicles; actin spin-down assay; ELISA-based spectrin binding assay; recombinant protein expression; transgenic parasite fluorescence microscopy\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution binding assays with quantified affinities using three orthogonal methods (IOV binding, actin co-sedimentation, ELISA), single lab\",\n      \"pmids\": [\"28320404\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SURF4.2 is present in the neck of the rhoptries of P. falciparum merozoites, is secreted into the parasitophorous vacuole, and is shed into culture supernatant upon schizont rupture. SURF4.2 forms a protein complex (named SURGE) with the rhoptry neck protein RON4 and the Glutamate Rich Protein GLURP, as shown by immunoprecipitation followed by mass spectrometry. The N-terminal cysteine-rich domain (CRD) of SURF4.2 mediates binding to the RBC membrane. Polyclonal antibodies against the extracellular domain (including CRD) of SURF4.2 partially inhibit merozoite invasion.\",\n      \"method\": \"Immunoprecipitation followed by mass spectrometry (co-IP/MS); antibody localization by immunofluorescence and immunoelectron microscopy; invasion inhibition assay with polyclonal antibodies\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP/MS identification of complex plus functional invasion inhibition assay, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"30092030\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"N-terminally Myc-tagged mini-SURF4.2 (containing the N-terminal region, TM region, and cytoplasmic region) was detected at Maurer's clefts by anti-Myc antibody staining, indicating that the N-terminal sequence of SURF4.2 is not cleaved during export and that elements required for export to Maurer's clefts are conserved between SURFIN4.1 and SURFIN4.2.\",\n      \"method\": \"Transgenic parasite lines expressing Myc-tagged mini-SURFIN4.2; immunofluorescence assay with anti-Myc antibody\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single IFA readout, single lab, finding is secondary to main SURFIN4.1 study\",\n      \"pmids\": [\"31028841\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Naturally acquired antibodies from children with malaria react with SURF4.2 at the parasitized RBC surface, and data indicate SURF4.2 may have a function during rosette formation, though this was not formally validated in the study.\",\n      \"method\": \"Serological profiling with peptide arrays; assessment of rosetting rate and surface reactivity using patient sera\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect serological evidence of surface exposure; rosette formation role explicitly noted as unvalidated\",\n      \"pmids\": [\"29459776\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"FCR3S1.2\"}]\n    }\n  ],\n  \"current_model\": \"SURF4.2 (PF3D7_0424400) is a type I transmembrane protein exported from the parasite to Maurer's clefts via a PEXEL-independent, transmembrane-domain-dependent mechanism, and further transported to the infected erythrocyte surface via its cytoplasmic tryptophan-rich (WR) domain; the WR domain directly binds RBC membrane skeletal components (spectrin and F-actin), and in merozoites SURF4.2 localizes to the rhoptry neck where it forms the SURGE complex with RON4 and GLURP, with its extracellular cysteine-rich domain mediating RBC membrane binding and contributing to merozoite invasion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SURF4.2 (PF3D7_0424400) is a Plasmodium falciparum type I transmembrane protein that operates at two stages of the intraerythrocytic cycle: it is exported to the surface of infected erythrocytes during blood-stage growth and relocalizes to the merozoite apex for invasion [#0]. During export, SURF4.2 traffics through Maurer's clefts to the infected-RBC surface by a PEXEL-independent route in which the transmembrane region is necessary and sufficient for delivery to the clefts, while the N-terminal sequence remains uncleaved [#2, #1]. Onward transport from Maurer's clefts to the erythrocyte surface then depends on the cytoplasmic tryptophan-rich (WR) domain [#4], which drives detergent-resistant membrane-skeleton association [#3]; the second WR domain (WRD2) binds the RBC membrane skeleton directly, engaging inside-out vesicles, F-actin and spectrin with sub-micromolar to low-micromolar affinity [#5]. In merozoites SURF4.2 localizes to the rhoptry neck and is secreted into the parasitophorous vacuole, where it assembles into the SURGE complex with the rhoptry neck protein RON4 and GLURP; its N-terminal extracellular cysteine-rich domain mediates RBC membrane binding, and antibodies against the extracellular domain partially inhibit merozoite invasion [#6]. Whether SURF4.2 has a role in rosette formation is a surface-antibody-based observation that was not functionally validated [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing that SURF4.2 reaches the infected-erythrocyte surface answered whether this protein is a parasite-derived surface antigen co-trafficked with known virulence proteins.\",\n      \"evidence\": \"Surface trypsinization plus mass spectrometry and IFA co-localization with PfEMP1 and RIFIN on live infected erythrocytes\",\n      \"pmids\": [\"15939796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking route and domain requirements not defined\", \"Functional role at the surface not tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Detecting SURF4.2 in Maurer's clefts identified the intermediate trafficking compartment on the path to the erythrocyte surface.\",\n      \"evidence\": \"Indirect immunofluorescence with Giemsa staining and transmission electron microscopy on infected erythrocytes\",\n      \"pmids\": [\"17255224\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single IFA method, no functional consequence tested\", \"Does not resolve how the protein enters or exits the clefts\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Domain-mapping resolved that SURF4.2 export is PEXEL-independent and driven by its transmembrane region, distinguishing it from canonical PEXEL-motif exported proteins.\",\n      \"evidence\": \"GFP-fusion deletion/replacement constructs in transgenic parasites with IFA and Triton X-100 fractionation Western blotting\",\n      \"pmids\": [\"21616162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism recognizing the TM region for export not identified\", \"Onward step to the surface not addressed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Biochemical fractionation linked the cytoplasmic WR domain to detergent-resistant/membrane-skeleton association, hinting at how SURF4.2 anchors at the erythrocyte cortex.\",\n      \"evidence\": \"Triton X-100 fractionation and Western blotting of recombinant SURF4.2 constructs with and without the WR domain\",\n      \"pmids\": [\"21616162\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single biochemical fractionation, no direct binding partner shown\", \"Functional consequence not demonstrated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Functional dissection showed the cytoplasmic WR-containing region is required for the final step of transport from Maurer's clefts to the iRBC surface, defining a two-stage export mechanism.\",\n      \"evidence\": \"Transgenic parasites with/without the intracellular region, proteinase K surface accessibility assay and IFA\",\n      \"pmids\": [\"26865830\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular partners at the surface delivery step not identified\", \"Does not quantify surface abundance or virulence impact\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"In vitro binding assays established a direct molecular interaction between SURF4.2 and the RBC membrane skeleton, providing the biochemical basis for its cortical anchoring.\",\n      \"evidence\": \"Recombinant WRD2 binding to inside-out vesicles, F-actin co-sedimentation, and ELISA-based spectrin binding with quantified affinities\",\n      \"pmids\": [\"28320404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding not demonstrated in the native cellular context\", \"Physiological consequence of skeleton binding for the host cell not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying rhoptry-neck localization and the SURGE complex extended SURF4.2's role beyond surface display to invasion, defining its partners and an invasion-relevant binding domain.\",\n      \"evidence\": \"Reciprocal co-IP/MS identifying RON4 and GLURP, immuno-EM localization, and antibody-based invasion inhibition assays\",\n      \"pmids\": [\"30092030\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and assembly order of the SURGE complex unknown\", \"Erythrocyte receptor for the CRD not identified\", \"Only partial invasion inhibition observed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Serological profiling confirmed SURF4.2 is an immune target at the infected-cell surface and raised the possibility of a rosetting role.\",\n      \"evidence\": \"Peptide-array serology with patient sera and rosetting-rate assessment\",\n      \"pmids\": [\"29459776\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Rosette role explicitly not functionally validated\", \"Indirect serological inference of surface exposure\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"FCR3S1.2\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Tagged mini-SURF4.2 confirmed the N-terminus is not cleaved during export and that Maurer's-cleft targeting elements are shared with the paralog SURFIN4.1.\",\n      \"evidence\": \"Myc-tagged mini-SURF4.2 transgenic parasites with anti-Myc IFA\",\n      \"pmids\": [\"31028841\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single IFA readout secondary to a SURFIN4.1 study\", \"Does not identify the export receptor for the shared signal\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The erythrocyte surface receptor engaged by the SURF4.2 extracellular cysteine-rich domain during invasion, and the causal contribution of its membrane-skeleton binding to host-cell remodeling or rosetting, remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No identified host receptor for the CRD\", \"SURGE complex assembly mechanism unresolved\", \"Rosetting role not functionally tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003779\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0030507\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0050839\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020030\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0020036\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0020002\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0020005\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0016020\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0046718\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0065002\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [\n      \"SURGE complex (SURF4.2 with RON4 and GLURP) [#6]\"\n    ],\n    \"partners\": [\n      \"RON4 (rhoptry neck protein) [#6]\",\n      \"GLURP (glutamate-rich protein) [#6]\",\n      \"RBC spectrin [#5]\",\n      \"RBC F-actin [#5]\",\n      \"RBC inside-out membrane vesicles [#5]\"\n    ],\n    \"other_free_text\": [\n      \"Type I transmembrane protein exported via a PEXEL-independent, transmembrane-domain-dependent route [#2].\",\n      \"Co-transported to the infected-erythrocyte surface with PfEMP1 and RIFIN [#0].\",\n      \"Cytoplasmic WR domain required for the Maurer's-cleft-to-surface transport step and confers Triton X-100 insolubility [#3, #4].\",\n      \"N-terminal extracellular cysteine-rich domain mediates RBC membrane binding and contributes to merozoite invasion [#6].\",\n      \"Target of naturally acquired antibodies at the infected-RBC surface, with an unvalidated possible role in rosette formation [#8].\",\n      \"Export/Maurer's-cleft targeting elements shared with the paralog SURFIN4.1 [#7].\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0424400","name":null,"product":"surface-associated interspersed protein 4.2 (SURFIN 4.2)","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"","evaluation":null}