{"gene":"PF3D7_1342500","run_date":"2026-09-08T14:19:06","timeline":{"discoveries":[{"year":2004,"finding":"SPECT1 is a microneme protein in P. berghei sporozoites required for cell traversal (passage through host cells) but not for direct hepatocyte invasion. Targeted disruption of spect shows that sporozoites lacking SPECT1 can infect hepatocytes normally in vitro but completely lack cell passage ability; liver infectivity is restored by depletion of Kupffer cells, indicating SPECT1 mediates traversal through the sinusoidal cell layer (primarily via Kupffer cells).","method":"Targeted gene disruption in P. berghei; in vitro cell invasion and traversal assays; Kupffer cell depletion experiment","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with specific cellular phenotype (traversal vs. invasion discrimination), validated by Kupffer cell depletion, foundational study replicated by subsequent work","pmids":["14737184"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2014,"finding":"The crystal structure of P. berghei SPECT1 (at 2.75 Å resolution) reveals a four-helix bundle with all helices in parallel or antiparallel alignment and a large, conserved, hydrophobic internal cavity that may constitute a ligand-binding site or indicate partial instability. SPECT1 has no sequence homology to proteins of known structure or function, making it a structurally novel protein.","method":"X-ray crystallography (2.75 Å resolution structure of truncated P. berghei SPECT1)","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with defined resolution, single study but direct structural determination","pmids":["25479287"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2016,"finding":"Structural comparison reveals that the four-helix bundle region of SPECT1 displays significant structural similarity to regions of mammalian sperm protein Izumo1, suggesting evolutionary or functional links between Plasmodium host cell traversal and gamete membrane fusion machinery.","method":"Crystal structure comparison / structural bioinformatics","journal":"Current biology : CB","confidence":"Low","confidence_rationale":"Tier 4 / Weak — structural similarity noted in a comparative structural paper, no functional validation of the similarity for SPECT1 mechanism","pmids":["27374339"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"In P. berghei, SPECT1 is required for the cell wounding that triggers NF-κB activation and inducible NO synthase expression in neighboring hepatocytes. When spect-null sporozoites (which cannot traverse host cells) are used, no NF-κB activation is observed in hepatocytes, demonstrating that SPECT1-dependent cell traversal is the upstream cause of the host innate immune response that limits parasite infection.","method":"Genetic epistasis using spect(-/-) P. berghei sporozoites; NF-κB reporter assays in primary hepatocytes and HepG2 cells; in vitro and in vivo infection assays","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic knockout epistasis with defined downstream pathway readout, single lab","pmids":["18322208"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2007,"finding":"Using spect(-/-) P. berghei sporozoites, traversal-independent hepatocyte infection was shown to be sufficient for CSP processing and presentation via MHC class I to CD8+ T cells, placing SPECT1-dependent traversal as dispensable for antigen presentation from infected (but not traversed) hepatocytes.","method":"Genetic epistasis using spect(-/-) P. berghei sporozoites; in vitro CD8+ T cell presentation assay with primary BALB/c hepatocytes","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO used as epistatic tool to dissect traversal-dependent vs. -independent antigen presentation, single lab","pmids":["17513754"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2017,"finding":"Genetic disruption of PfSPECT1 (PF3D7_1342500) in P. falciparum produces sporozoites that cannot perform cell traversal in vitro and cannot establish normal liver infection in humanized mice, demonstrating that SPECT1 is essential for transcellular migration and in vivo liver infection by the human malaria parasite. Loss of PfSPECT1 did not affect P. falciparum growth in erythrocytes.","method":"Targeted gene disruption in P. falciparum; in vitro traversal assay; in vivo liver infection in humanized mice; erythrocyte growth assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with multiple orthogonal phenotypic readouts (in vitro traversal, in vivo humanized mouse liver infection, erythrocyte growth control), directly on PF3D7_1342500","pmids":["28355563"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"NF54"}]},{"year":2010,"finding":"Synthetic peptide mapping of P. falciparum SPECT1 identified 3 high-activity binding peptides (HABPs) to HeLa cells, all predominantly α-helical. Immunofluorescence with antibodies against these peptides confirmed the presence of SPECT1 in sporozoite micronemes and in the sporozoite membrane.","method":"Synthetic peptide binding assay to HeLa cells; immunofluorescence assay with anti-peptide antibodies; 1H NMR structural characterization","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — peptide binding assay and IFA localization, multiple methods in single lab study","pmids":["20933029"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"SPECT1 (PF3D7_1342500) is a microneme-localized four-helix bundle protein in Plasmodium sporozoites that is essential for cell traversal (transcellular migration through host cells including Kupffer cells and sinusoidal endothelium) but dispensable for direct hepatocyte invasion or erythrocytic growth; its traversal activity is required for efficient liver infection in vivo, and it acts upstream of host NF-κB/iNOS innate immune activation triggered by cell wounding."},"narrative":{"mechanistic_narrative":"SPECT1 (PF3D7_1342500) is a microneme-localized sporozoite protein that is essential for cell traversal — the transcellular migration of Plasmodium sporozoites through host cells — but is dispensable for direct hepatocyte invasion and erythrocytic growth [PMID:14737184, PMID:28355563]. In P. berghei, targeted disruption abolishes cell passage while leaving productive hepatocyte infection intact, and liver infectivity of the mutant is restored by depleting Kupffer cells, showing that SPECT1-dependent traversal is required to cross the sinusoidal cell layer [PMID:14737184]; in P. falciparum, disruption of PF3D7_1342500 similarly eliminates traversal in vitro and blocks liver infection in humanized mice without affecting erythrocyte growth [PMID:28355563]. Functionally, SPECT1-mediated traversal acts upstream of host innate immunity: spect-null sporozoites fail to wound host cells and consequently do not trigger NF-κB activation and inducible NO synthase expression in hepatocytes, whereas this traversal is dispensable for CSP processing and MHC class I presentation to CD8+ T cells from directly infected hepatocytes [PMID:18322208, PMID:17513754]. Structurally, SPECT1 is a novel four-helix bundle protein with a large conserved hydrophobic internal cavity and no sequence homology to proteins of known function [PMID:25479287]. The molecular partners and biochemical mechanism by which SPECT1 executes membrane traversal have not been characterized in the available corpus.","teleology":[{"year":2004,"claim":"Established that SPECT1 defines a distinct sporozoite activity — cell traversal — separable from hepatocyte invasion, resolving whether migration through cells and productive infection are the same process.","evidence":"Targeted gene disruption in P. berghei with in vitro traversal/invasion assays and Kupffer cell depletion","pmids":["14737184"],"confidence":"High","gaps":["Molecular mechanism of membrane traversal not defined","No host ligand or binding partner identified","Does not address relevance in human-infecting species"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2007,"claim":"Determined that traversal is dispensable for antigen presentation, showing that directly infected (non-traversed) hepatocytes are sufficient to process CSP and present via MHC class I to CD8+ T cells.","evidence":"Epistasis with spect(-/-) P. berghei sporozoites in CD8+ T cell presentation assays using primary hepatocytes","pmids":["17513754"],"confidence":"Medium","gaps":["Single-lab result","Does not establish contribution of traversal to in vivo immunity"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2008,"claim":"Placed SPECT1-dependent traversal upstream of host innate immune activation, demonstrating that cell wounding during traversal — not invasion — triggers hepatocyte NF-κB and iNOS responses.","evidence":"Genetic epistasis with spect(-/-) P. berghei sporozoites and NF-κB reporter assays in primary hepatocytes and HepG2 cells","pmids":["18322208"],"confidence":"Medium","gaps":["Molecular trigger of wounding-induced NF-κB not identified","Single-lab result"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2010,"claim":"Provided direct localization and host-cell binding evidence, confirming SPECT1 resides in sporozoite micronemes and membrane and that defined α-helical peptides can bind host cells.","evidence":"Synthetic peptide binding to HeLa cells, anti-peptide immunofluorescence, and 1H NMR of P. falciparum SPECT1 peptides","pmids":["20933029"],"confidence":"Medium","gaps":["Peptide binding does not identify a physiological host receptor","Binding relevance to traversal mechanism untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"Solved the atomic structure, revealing SPECT1 as a structurally novel four-helix bundle with a conserved hydrophobic internal cavity, a candidate ligand-binding feature.","evidence":"X-ray crystallography at 2.75 Å of truncated P. berghei SPECT1","pmids":["25479287"],"confidence":"High","gaps":["No ligand identified for the internal cavity","Structure from truncated construct","Mechanistic role of the fold in traversal unresolved"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2016,"claim":"Noted a structural resemblance of the four-helix bundle to mammalian Izumo1, raising a possible link between traversal machinery and membrane fusion.","evidence":"Comparative structural bioinformatics","pmids":["27374339"],"confidence":"Low","gaps":["Structural similarity not functionally validated for SPECT1","No evidence SPECT1 mediates membrane fusion"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"claim":"Confirmed the traversal role in the human malaria parasite, showing PfSPECT1 (PF3D7_1342500) is essential for transcellular migration and in vivo liver infection but not erythrocytic growth.","evidence":"Targeted gene disruption in P. falciparum NF54 with in vitro traversal, humanized-mouse liver infection, and erythrocyte growth assays","pmids":["28355563"],"confidence":"High","gaps":["Molecular partners of PfSPECT1 not defined","Biochemical activity during traversal unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":"NF54"}]},{"year":null,"claim":"The biochemical mechanism by which SPECT1 enables membrane traversal — its molecular partners, whether the hydrophobic cavity binds a physiological ligand, and how it disrupts host membranes — remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No physiological host or parasite binding partner identified","Function of the conserved internal cavity untested","Mechanistic basis of cell wounding unknown"],"attribution":[]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":[],"other_free_text":["Structurally novel four-helix bundle with a large conserved hydrophobic internal cavity; no sequence homology to proteins of known function [#1]","Four-helix bundle shows structural similarity to mammalian sperm protein Izumo1 [#2]","SPECT1-dependent cell traversal acts upstream of host NF-κB activation and iNOS induction in hepatocytes [#3]","Traversal is dispensable for CSP processing and MHC class I presentation to CD8+ T cells [#4]","Liver infectivity of spect-null P. berghei restored by Kupffer cell depletion, implicating traversal of the sinusoidal cell layer [#0]","Dispensable for erythrocytic growth in P. falciparum [#5]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"14737184","id":"PMC_14737184","title":"Cell-passage activity is required for the malarial parasite to cross the liver sinusoidal cell layer.","date":"2004","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/14737184","citation_count":216,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"28355563","id":"PMC_28355563","title":"Cell Traversal Activity Is Important for Plasmodium falciparum Liver Infection in Humanized Mice.","date":"2017","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/28355563","citation_count":76,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17513754","id":"PMC_17513754","title":"Plasmodium berghei-infected primary hepatocytes process and present the circumsporozoite protein to specific CD8+ T cells in vitro.","date":"2007","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/17513754","citation_count":73,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17041140","id":"PMC_17041140","title":"Developmental biology of sporozoite-host interactions in Plasmodium falciparum malaria: implications for vaccine design.","date":"2006","source":"Clinical microbiology reviews","url":"https://pubmed.ncbi.nlm.nih.gov/17041140","citation_count":49,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"18322208","id":"PMC_18322208","title":"Sporozoite-mediated hepatocyte wounding limits Plasmodium parasite development via MyD88-mediated NF-kappa B activation and inducible NO synthase expression.","date":"2008","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/18322208","citation_count":33,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"27374339","id":"PMC_27374339","title":"The structure of sperm Izumo1 reveals unexpected similarities with Plasmodium invasion proteins.","date":"2016","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/27374339","citation_count":33,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"20933029","id":"PMC_20933029","title":"Biological and structural characteristics of the binding peptides from the sporozoite proteins essential for cell traversal (SPECT)-1 and -2.","date":"2010","source":"Peptides","url":"https://pubmed.ncbi.nlm.nih.gov/20933029","citation_count":16,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT","SPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"25479287","id":"PMC_25479287","title":"Structure of the essential Plasmodium host cell traversal protein SPECT1.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25479287","citation_count":13,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"38218737","id":"PMC_38218737","title":"Naturally acquired antibodies against Plasmodium vivax pre-erythrocytic stage vaccine antigens inhibit sporozoite invasion of human hepatocytes in vitro.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/38218737","citation_count":5,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"34025684","id":"PMC_34025684","title":"Identification, Selection and Immune Assessment of Liver Stage CD8 T Cell Epitopes From Plasmodium falciparum.","date":"2021","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/34025684","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"37703302","id":"PMC_37703302","title":"Preliminary characterization of Plasmodium vivax sporozoite antigens as pre-erythrocytic vaccine candidates.","date":"2023","source":"PLoS neglected tropical diseases","url":"https://pubmed.ncbi.nlm.nih.gov/37703302","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"38277340","id":"PMC_38277340","title":"Longitudinal analysis of antibody responses to Plasmodium vivax sporozoite antigens following natural infection.","date":"2024","source":"PLoS neglected tropical diseases","url":"https://pubmed.ncbi.nlm.nih.gov/38277340","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["PvSPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"42220505","id":"PMC_42220505","title":"Bivalent virus-like particles expressing SPECT1 and CSP trigger pre-erythrocytic malaria immunity and protect against transgenic Plasmodium falciparum sporozoite challenge in mice.","date":"2026","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/42220505","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SPECT","SPECT1","PfSPECT1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9204,"output_tokens":1998,"usd":0.028791,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7288,"output_tokens":2942,"usd":0.054995,"stage2_stop_reason":"end_turn"},"total_usd":0.083786,"stage1_batch_id":"msgbatch_011BPjN2BL33F8cJXD1r7V7T","stage2_batch_id":"msgbatch_01Qwg6vP7qxkpL6Gsc7tajsb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"SPECT1 is a microneme protein in P. berghei sporozoites required for cell traversal (passage through host cells) but not for direct hepatocyte invasion. Targeted disruption of spect shows that sporozoites lacking SPECT1 can infect hepatocytes normally in vitro but completely lack cell passage ability; liver infectivity is restored by depletion of Kupffer cells, indicating SPECT1 mediates traversal through the sinusoidal cell layer (primarily via Kupffer cells).\",\n      \"method\": \"Targeted gene disruption in P. berghei; in vitro cell invasion and traversal assays; Kupffer cell depletion experiment\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with specific cellular phenotype (traversal vs. invasion discrimination), validated by Kupffer cell depletion, foundational study replicated by subsequent work\",\n      \"pmids\": [\"14737184\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The crystal structure of P. berghei SPECT1 (at 2.75 Å resolution) reveals a four-helix bundle with all helices in parallel or antiparallel alignment and a large, conserved, hydrophobic internal cavity that may constitute a ligand-binding site or indicate partial instability. SPECT1 has no sequence homology to proteins of known structure or function, making it a structurally novel protein.\",\n      \"method\": \"X-ray crystallography (2.75 Å resolution structure of truncated P. berghei SPECT1)\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with defined resolution, single study but direct structural determination\",\n      \"pmids\": [\"25479287\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Structural comparison reveals that the four-helix bundle region of SPECT1 displays significant structural similarity to regions of mammalian sperm protein Izumo1, suggesting evolutionary or functional links between Plasmodium host cell traversal and gamete membrane fusion machinery.\",\n      \"method\": \"Crystal structure comparison / structural bioinformatics\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — structural similarity noted in a comparative structural paper, no functional validation of the similarity for SPECT1 mechanism\",\n      \"pmids\": [\"27374339\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In P. berghei, SPECT1 is required for the cell wounding that triggers NF-κB activation and inducible NO synthase expression in neighboring hepatocytes. When spect-null sporozoites (which cannot traverse host cells) are used, no NF-κB activation is observed in hepatocytes, demonstrating that SPECT1-dependent cell traversal is the upstream cause of the host innate immune response that limits parasite infection.\",\n      \"method\": \"Genetic epistasis using spect(-/-) P. berghei sporozoites; NF-κB reporter assays in primary hepatocytes and HepG2 cells; in vitro and in vivo infection assays\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic knockout epistasis with defined downstream pathway readout, single lab\",\n      \"pmids\": [\"18322208\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Using spect(-/-) P. berghei sporozoites, traversal-independent hepatocyte infection was shown to be sufficient for CSP processing and presentation via MHC class I to CD8+ T cells, placing SPECT1-dependent traversal as dispensable for antigen presentation from infected (but not traversed) hepatocytes.\",\n      \"method\": \"Genetic epistasis using spect(-/-) P. berghei sporozoites; in vitro CD8+ T cell presentation assay with primary BALB/c hepatocytes\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO used as epistatic tool to dissect traversal-dependent vs. -independent antigen presentation, single lab\",\n      \"pmids\": [\"17513754\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Genetic disruption of PfSPECT1 (PF3D7_1342500) in P. falciparum produces sporozoites that cannot perform cell traversal in vitro and cannot establish normal liver infection in humanized mice, demonstrating that SPECT1 is essential for transcellular migration and in vivo liver infection by the human malaria parasite. Loss of PfSPECT1 did not affect P. falciparum growth in erythrocytes.\",\n      \"method\": \"Targeted gene disruption in P. falciparum; in vitro traversal assay; in vivo liver infection in humanized mice; erythrocyte growth assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with multiple orthogonal phenotypic readouts (in vitro traversal, in vivo humanized mouse liver infection, erythrocyte growth control), directly on PF3D7_1342500\",\n      \"pmids\": [\"28355563\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"NF54\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Synthetic peptide mapping of P. falciparum SPECT1 identified 3 high-activity binding peptides (HABPs) to HeLa cells, all predominantly α-helical. Immunofluorescence with antibodies against these peptides confirmed the presence of SPECT1 in sporozoite micronemes and in the sporozoite membrane.\",\n      \"method\": \"Synthetic peptide binding assay to HeLa cells; immunofluorescence assay with anti-peptide antibodies; 1H NMR structural characterization\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — peptide binding assay and IFA localization, multiple methods in single lab study\",\n      \"pmids\": [\"20933029\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"SPECT1 (PF3D7_1342500) is a microneme-localized four-helix bundle protein in Plasmodium sporozoites that is essential for cell traversal (transcellular migration through host cells including Kupffer cells and sinusoidal endothelium) but dispensable for direct hepatocyte invasion or erythrocytic growth; its traversal activity is required for efficient liver infection in vivo, and it acts upstream of host NF-κB/iNOS innate immune activation triggered by cell wounding.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SPECT1 (PF3D7_1342500) is a microneme-localized sporozoite protein that is essential for cell traversal — the transcellular migration of Plasmodium sporozoites through host cells — but is dispensable for direct hepatocyte invasion and erythrocytic growth [#0, #5]. In P. berghei, targeted disruption abolishes cell passage while leaving productive hepatocyte infection intact, and liver infectivity of the mutant is restored by depleting Kupffer cells, showing that SPECT1-dependent traversal is required to cross the sinusoidal cell layer [#0]; in P. falciparum, disruption of PF3D7_1342500 similarly eliminates traversal in vitro and blocks liver infection in humanized mice without affecting erythrocyte growth [#5]. Functionally, SPECT1-mediated traversal acts upstream of host innate immunity: spect-null sporozoites fail to wound host cells and consequently do not trigger NF-\\u03baB activation and inducible NO synthase expression in hepatocytes, whereas this traversal is dispensable for CSP processing and MHC class I presentation to CD8+ T cells from directly infected hepatocytes [#3, #4]. Structurally, SPECT1 is a novel four-helix bundle protein with a large conserved hydrophobic internal cavity and no sequence homology to proteins of known function [#1]. The molecular partners and biochemical mechanism by which SPECT1 executes membrane traversal have not been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that SPECT1 defines a distinct sporozoite activity — cell traversal — separable from hepatocyte invasion, resolving whether migration through cells and productive infection are the same process.\",\n      \"evidence\": \"Targeted gene disruption in P. berghei with in vitro traversal/invasion assays and Kupffer cell depletion\",\n      \"pmids\": [\"14737184\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of membrane traversal not defined\", \"No host ligand or binding partner identified\", \"Does not address relevance in human-infecting species\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Determined that traversal is dispensable for antigen presentation, showing that directly infected (non-traversed) hepatocytes are sufficient to process CSP and present via MHC class I to CD8+ T cells.\",\n      \"evidence\": \"Epistasis with spect(-/-) P. berghei sporozoites in CD8+ T cell presentation assays using primary hepatocytes\",\n      \"pmids\": [\"17513754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab result\", \"Does not establish contribution of traversal to in vivo immunity\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Placed SPECT1-dependent traversal upstream of host innate immune activation, demonstrating that cell wounding during traversal — not invasion — triggers hepatocyte NF-\\u03baB and iNOS responses.\",\n      \"evidence\": \"Genetic epistasis with spect(-/-) P. berghei sporozoites and NF-\\u03baB reporter assays in primary hepatocytes and HepG2 cells\",\n      \"pmids\": [\"18322208\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular trigger of wounding-induced NF-\\u03baB not identified\", \"Single-lab result\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided direct localization and host-cell binding evidence, confirming SPECT1 resides in sporozoite micronemes and membrane and that defined \\u03b1-helical peptides can bind host cells.\",\n      \"evidence\": \"Synthetic peptide binding to HeLa cells, anti-peptide immunofluorescence, and 1H NMR of P. falciparum SPECT1 peptides\",\n      \"pmids\": [\"20933029\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Peptide binding does not identify a physiological host receptor\", \"Binding relevance to traversal mechanism untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Solved the atomic structure, revealing SPECT1 as a structurally novel four-helix bundle with a conserved hydrophobic internal cavity, a candidate ligand-binding feature.\",\n      \"evidence\": \"X-ray crystallography at 2.75 \\u00c5 of truncated P. berghei SPECT1\",\n      \"pmids\": [\"25479287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No ligand identified for the internal cavity\", \"Structure from truncated construct\", \"Mechanistic role of the fold in traversal unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Noted a structural resemblance of the four-helix bundle to mammalian Izumo1, raising a possible link between traversal machinery and membrane fusion.\",\n      \"evidence\": \"Comparative structural bioinformatics\",\n      \"pmids\": [\"27374339\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Structural similarity not functionally validated for SPECT1\", \"No evidence SPECT1 mediates membrane fusion\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Confirmed the traversal role in the human malaria parasite, showing PfSPECT1 (PF3D7_1342500) is essential for transcellular migration and in vivo liver infection but not erythrocytic growth.\",\n      \"evidence\": \"Targeted gene disruption in P. falciparum NF54 with in vitro traversal, humanized-mouse liver infection, and erythrocyte growth assays\",\n      \"pmids\": [\"28355563\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular partners of PfSPECT1 not defined\", \"Biochemical activity during traversal unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"NF54\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The biochemical mechanism by which SPECT1 enables membrane traversal — its molecular partners, whether the hydrophobic cavity binds a physiological ligand, and how it disrupts host membranes — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No physiological host or parasite binding partner identified\", \"Function of the conserved internal cavity untested\", \"Mechanistic basis of cell wounding unknown\"],\n      \"attribution\": []\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020009\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0016020\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0090675\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": [\n      \"Structurally novel four-helix bundle with a large conserved hydrophobic internal cavity; no sequence homology to proteins of known function [#1]\",\n      \"Four-helix bundle shows structural similarity to mammalian sperm protein Izumo1 [#2]\",\n      \"SPECT1-dependent cell traversal acts upstream of host NF-\\u03baB activation and iNOS induction in hepatocytes [#3]\",\n      \"Traversal is dispensable for CSP processing and MHC class I presentation to CD8+ T cells [#4]\",\n      \"Liver infectivity of spect-null P. berghei restored by Kupffer cell depletion, implicating traversal of the sinusoidal cell layer [#0]\",\n      \"Dispensable for erythrocytic growth in P. falciparum [#5]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1342500","name":null,"product":"sporozoite protein essential for cell traversal","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1355600","name":null,"product":"sporozoite protein essential for cell traversal","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1258900","name":null,"product":"sporozoite protein essential for cell traversal, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"SPECT","evaluation":null}