{"gene":"PF3D7_1136900","run_date":"2026-09-08T12:51:28","timeline":{"discoveries":[{"year":2005,"finding":"SUB2 (PfSUB2) was identified as the merozoite surface sheddase responsible for ectodomain shedding of MSP1 and AMA1. It is stored in micronemes, secreted onto the parasite surface upon merozoite release, and translocates to the posterior pole in an actin-dependent manner. The SUB2 propeptide binds specifically to mature parasite-derived SUB2 and acts as a potent, selective inhibitor of MSP1 and AMA1 shedding, directly establishing SUB2 as the sheddase.","method":"Recombinant propeptide binding assay, shedding inhibition assay, immunofluorescence localization, actin inhibitor experiments","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (propeptide binding, functional shedding inhibition, localization), directly establishing enzymatic identity and trafficking","pmids":["16322767"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1999,"finding":"SUB2 (PfSUB2) is encoded by a single-copy gene and expressed as a large type I integral membrane protein that undergoes extensive post-translational processing; the terminal processing product is expressed in an apical location in merozoites, and SUB2 was proposed as a candidate for the MSP1 maturase based on its subtilisin-like active site and dense granule localization.","method":"Gene cloning, Western blot, immunofluorescence/immunoelectron microscopy showing dense granule localization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization by microscopy and post-translational processing demonstrated, but candidate role for MSP1 maturation was not yet experimentally confirmed in this paper","pmids":["10339607"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1999,"finding":"SUB2 (PfSUB-2) is a second P. falciparum subtilisin-like protein expressed in merozoites as a large type I integral membrane protein that undergoes extensive post-translational processing, with the terminal product in an apical location.","method":"Gene identification, Western blot, immunofluorescence localization in merozoites","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct protein characterization and localization by two independent groups (PMID:10339607 and 10551362) with consistent findings","pmids":["10551362"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2004,"finding":"SUB2 in P. berghei (PbSUB2) is essential for red blood cell invasion; knockout parasites could not be recovered despite successful tagging at the locus, confirming essentiality for the intraerythrocytic cycle. Kinetics of expression and subcellular localization are consistent with a central role in erythrocyte invasion.","method":"Gene targeting/knockout attempt in P. berghei, tagging of Pbsub2 locus, immunofluorescence localization","journal":"Cellular microbiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic essentiality established by failed knockout with successful locus modification as control, replicated concept across species","pmids":["14678331"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium yoelii","strain":""}]},{"year":2006,"finding":"SUB2 (PfSUB2) sheds PTRAMP (Plasmodium thrombospondin related apical merozoite protein) from the merozoite surface upon erythrocyte invasion, identifying PTRAMP as a substrate of SUB2.","method":"Shedding assay, Western blot of surface proteins during invasion","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single study demonstrating SUB2-mediated shedding of a specific substrate; abstract-level detail is limited","pmids":["16879884"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"SUB2 (PfSUB2) mediates the secondary (juxtamembrane) processing of MSP1 during erythrocyte invasion; regulated spatiotemporal maturation of MSP1 by SUB2 is essential for parasite growth, as replacement of the secondary processing site with a PfSUB1-sensitive site is deleterious.","method":"Targeted homologous recombination to modify MSP1 processing site, parasite growth assay","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — site-specific mutagenesis of substrate cleavage site via targeted recombination with functional growth readout in a single rigorous study","pmids":["20735778"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"SUB2 (PfSUB2) cleaves AMA1 predominantly at a juxtamembrane site; the position of cleavage is determined primarily by distance from the parasite membrane rather than primary sequence. Mutations blocking PfSUB2-mediated shedding could not be stably introduced into the genomic pfama1 locus, establishing that some AMA1 shedding by SUB2 is essential. Parasites expressing shedding-resistant AMA1 show enhanced sensitivity to antibody-mediated invasion inhibition.","method":"Targeted homologous recombination, mutagenesis of AMA1 cleavage site, invasion assay, antibody inhibition assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic manipulation of substrate cleavage site with multiple functional readouts (essentiality, antibody sensitivity) in a single rigorous study","pmids":["22194692"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"The solution NMR structure of the conserved inhibitory prodomain of SUB2 (PfSUB2) was determined. Despite no detectable sequence homology, the prosub2 domain has structural similarity to bacterial and mammalian subtilisin-like prodomains, suggesting a conserved binding interface with the catalytic domain and providing insight into processing site locations.","method":"Solution NMR structure determination of recombinant prosub2 domain","journal":"Proteins","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR structure determined but functional validation of the binding interface was inferred by comparison, not experimentally confirmed in this study","pmids":["23011838"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"Trafficking of SUB2 (PfSUB2) to micronemes requires its transmembrane domain; the cytoplasmic domain is essential for surface translocation of the protease to the parasite posterior following discharge from micronemes. Autocatalytic protease activity is required for trafficking of PfSUB2 beyond an early compartment in the secretory pathway. Authentic promoter activity within the intergenic region 5' of the pfsub2 locus is important for correct localization.","method":"Truncation/domain-swap constructs, transfection, live-cell imaging, mutagenesis of autocatalytic site","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — domain-specific mutagenesis with multiple functional localization readouts in a single focused study with orthogonal approaches","pmids":["23834729"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"SUB2 (PfSUB2) localizes to osmiophilic bodies in P. falciparum female gametocytes, as determined by fluorescent reporter gene fusions and specific antibodies using comparative proteomics of pfg377-disrupted parasites that lack osmiophilic bodies.","method":"Comparative label-free proteomics of wild-type vs. pfg377-KO gametocytes, fluorescent reporter fusions, immunofluorescence","journal":"Molecular & cellular proteomics : MCP","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — localization established by orthogonal methods (proteomics + reporter fusion + antibody) in a single study, but functional consequence of SUB2 in osmiophilic bodies not determined","pmids":["27432909"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"Genetic depletion of SUB2 in P. falciparum abolishes shedding of multiple parasite surface proteins and identifies previously unrecognized substrates. SUB2-null merozoite interaction with RBCs leads to either abortive invasion with rapid RBC lysis, or successful entry but developmental arrest. Selective failure to shed MSP1 reduces intracellular replication, while conditional ablation of the substrate AMA1 produces host RBC lysis. SUB2 activity is critical for host RBC membrane sealing following parasite internalization.","method":"Conditional genetic depletion of SUB2, proteomics for substrate identification, live-cell imaging of invasion, electron microscopy","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional knockout with multiple orthogonal readouts (proteomic substrate identification, invasion assays, ultrastructural imaging, substrate-specific conditional lines), rigorous study","pmids":["33287958"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2002,"finding":"In P. berghei ookinetes, a SUB2 ortholog (PbSub2) is released during ookinete migration through midgut epithelial cells, suggesting a role for SUB2 in ookinete-stage biology.","method":"Immunofluorescence/localization during ookinete midgut invasion","journal":"Insect biochemistry and molecular biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single localization observation during ookinete invasion, no functional validation of SUB2 activity at this stage","pmids":["12225921"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]}],"current_model":"SUB2 (PF3D7_1136900) is an integral membrane subtilisin-like serine protease stored in micronemes that is secreted onto the merozoite surface at egress and translocates actin-dependently to the posterior pole, where it acts as the essential sheddase cleaving multiple surface proteins including MSP1 and AMA1 at juxtamembrane sites; autocatalytic processing is required for secretory pathway trafficking, the transmembrane domain mediates micronemal targeting, and the cytoplasmic domain drives posterior surface translocation; conditional depletion of SUB2 abolishes substrate shedding, causes abortive invasion or developmental arrest, and prevents host RBC membrane sealing, establishing SUB2 as essential for both successful erythrocyte invasion and post-invasion vacuole integrity."},"narrative":{"mechanistic_narrative":"SUB2 (PF3D7_1136900) is an essential subtilisin-like serine protease that acts as the merozoite surface sheddase governing erythrocyte invasion in Plasmodium [PMID:16322767, PMID:33287958]. Expressed as a single-copy, large type I integral membrane protein that undergoes extensive autocatalytic post-translational processing, SUB2 is stored apically in micronemes and secreted onto the merozoite surface at egress, from where it translocates actin-dependently to the parasite posterior pole [PMID:16322767, PMID:10339607, PMID:23834729]. There it cleaves multiple surface proteins at juxtamembrane positions—including MSP1, AMA1, and PTRAMP—with cleavage site selection determined primarily by distance from the parasite membrane rather than primary sequence [PMID:16322767, PMID:16879884, PMID:20735778, PMID:22194692]. Its enzymatic identity is established by the SUB2 propeptide, which binds mature parasite-derived SUB2 and selectively inhibits MSP1 and AMA1 shedding [PMID:16322767, PMID:23011838]. Trafficking is domain-encoded: autocatalytic activity is required to progress beyond an early secretory compartment, the transmembrane domain directs micronemal targeting, and the cytoplasmic domain drives posterior surface translocation [PMID:23834729]. SUB2 is genetically essential for the intraerythrocytic cycle in both P. falciparum and P. berghei; conditional depletion abolishes substrate shedding and causes either abortive invasion with RBC lysis or successful entry followed by developmental arrest, and SUB2 activity is required for sealing of the host RBC membrane after internalization [PMID:14678331, PMID:22194692, PMID:33287958].","teleology":[{"year":1999,"claim":"Establishing that SUB2 exists as a distinct, second subtilisin-like protease of P. falciparum defined the molecular entity and raised the question of its enzymatic role in merozoites.","evidence":"Gene cloning, Western blot, and immunofluorescence/immunoelectron microscopy in P. falciparum merozoites by two independent groups","pmids":["10339607","10551362"],"confidence":"Medium","gaps":["Enzymatic substrate not experimentally confirmed","Proposed MSP1 maturase role remained a hypothesis","Micronemal versus dense-granule assignment not yet resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2002,"claim":"Detection of a SUB2 ortholog released during ookinete midgut migration hinted that SUB2 function extends beyond the blood-stage merozoite.","evidence":"Immunofluorescence localization during P. berghei ookinete invasion of midgut epithelium","pmids":["12225921"],"confidence":"Low","gaps":["Single localization observation with no functional validation","No substrate or phenotype defined at the ookinete stage","Relevance to P. falciparum not addressed"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2004,"claim":"Genetic knockout attempts answered whether SUB2 is dispensable, establishing its essentiality for the intraerythrocytic cycle.","evidence":"Failed gene knockout with successful control tagging of the Pbsub2 locus plus localization in P. berghei/P. yoelii","pmids":["14678331"],"confidence":"High","gaps":["Molecular basis of essentiality not defined","Substrates not identified in this study","Does not distinguish an invasion role from other functions"],"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium yoelii","strain":""}]},{"year":2005,"claim":"Directly identifying SUB2 as the merozoite surface sheddase resolved its enzymatic identity and placed it in the invasion pathway.","evidence":"Recombinant propeptide binding and selective shedding inhibition, immunofluorescence localization, and actin-inhibitor experiments in P. falciparum","pmids":["16322767"],"confidence":"High","gaps":["Full substrate repertoire not enumerated","Mechanism of actin-dependent posterior translocation not resolved","Cleavage site determinants not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"claim":"Identifying PTRAMP as a SUB2 substrate broadened the sheddase's target set beyond MSP1 and AMA1.","evidence":"Shedding assay and Western blot of surface proteins during P. falciparum invasion","pmids":["16879884"],"confidence":"Medium","gaps":["Single-study substrate assignment","Functional consequence of PTRAMP shedding not tested","Cleavage site not mapped"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Defining that SUB2 cleaves AMA1 and MSP1 at juxtamembrane sites chosen by membrane distance rather than sequence explained how one protease processes multiple substrates, and confirmed shedding is functionally essential.","evidence":"Targeted homologous recombination and cleavage-site mutagenesis of MSP1 and AMA1 with growth, invasion, and antibody-inhibition assays in P. falciparum","pmids":["20735778","22194692"],"confidence":"High","gaps":["Structural basis of distance-based recognition not determined","Interplay between substrates during invasion not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"claim":"The NMR structure of the SUB2 inhibitory prodomain provided a structural rationale for propeptide-mediated inhibition and processing site placement.","evidence":"Solution NMR structure determination of the recombinant prosub2 domain","pmids":["23011838"],"confidence":"Medium","gaps":["Binding interface with the catalytic domain inferred by comparison, not experimentally confirmed","No structure of the mature catalytic domain","No enzyme–substrate complex"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"claim":"Dissecting SUB2 trafficking assigned specific transport steps to defined protein regions, explaining how the sheddase reaches micronemes and then the posterior surface.","evidence":"Truncation/domain-swap constructs, transfection, live-cell imaging, and autocatalytic-site mutagenesis in P. falciparum","pmids":["23834729"],"confidence":"High","gaps":["Molecular machinery recognizing the transmembrane and cytoplasmic signals unknown","Mechanistic link between autocatalysis and secretory progression not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"claim":"Localizing SUB2 to osmiophilic bodies of female gametocytes indicated a potential transmission-stage compartmentalization distinct from the merozoite microneme.","evidence":"Comparative proteomics of pfg377-disrupted gametocytes with fluorescent reporter fusions and immunofluorescence in P. falciparum","pmids":["27432909"],"confidence":"Medium","gaps":["Functional role of SUB2 in osmiophilic bodies not determined","No substrate identified at this stage","Relationship to blood-stage sheddase function unclear"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"claim":"Conditional depletion defined the full phenotypic consequences of losing SUB2, distinguishing invasion, replication, and RBC-sealing roles and expanding its substrate list.","evidence":"Conditional genetic depletion of SUB2 with proteomic substrate identification, live-cell invasion imaging, electron microscopy, and substrate-specific conditional lines in P. falciparum","pmids":["33287958"],"confidence":"High","gaps":["Mechanism linking shedding to RBC membrane sealing not defined","Identities and roles of newly recognized substrates not fully characterized"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How SUB2 achieves its distance-based juxtamembrane cleavage specificity structurally, and what its function is in gametocyte osmiophilic bodies and ookinetes, remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of the catalytic domain or an enzyme–substrate complex","No functional assignment of SUB2 at transmission stages","Molecular basis of RBC membrane sealing dependence on SUB2 unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["MSP1 (SUBSTRATE)","AMA1 (SUBSTRATE)","PTRAMP (SUBSTRATE)","SUB2 PROPEPTIDE/PRODOMAIN (AUTOINHIBITORY)"],"other_free_text":["Single-copy gene encoding a large type I integral membrane subtilisin-like serine protease [#1, #2]","Autocatalytic processing required for progression beyond an early secretory compartment; transmembrane domain directs micronemal targeting; cytoplasmic domain drives posterior surface translocation [#8]","Cleaves substrates at juxtamembrane sites selected by distance from the parasite membrane rather than primary sequence [#6]","Genetically essential for the intraerythrocytic cycle in P. falciparum and P. berghei; depletion causes abortive invasion, developmental arrest, and failure of host RBC membrane sealing [#3, #10]","Prodomain NMR structure shows conserved subtilisin prodomain fold despite no detectable sequence homology [#7]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"16322767","id":"PMC_16322767","title":"Molecular identification of a malaria merozoite surface 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2","PfSUB2"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11328,"output_tokens":3338,"usd":0.042027,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9179,"output_tokens":4079,"usd":0.073935,"stage2_stop_reason":"end_turn"},"total_usd":0.115962,"stage1_batch_id":"msgbatch_01DisAaTypwmC8QwdMBuePHo","stage2_batch_id":"msgbatch_0184zxZTqxiEfdYYfPMfkqjb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"SUB2 (PfSUB2) was identified as the merozoite surface sheddase responsible for ectodomain shedding of MSP1 and AMA1. It is stored in micronemes, secreted onto the parasite surface upon merozoite release, and translocates to the posterior pole in an actin-dependent manner. The SUB2 propeptide binds specifically to mature parasite-derived SUB2 and acts as a potent, selective inhibitor of MSP1 and AMA1 shedding, directly establishing SUB2 as the sheddase.\",\n      \"method\": \"Recombinant propeptide binding assay, shedding inhibition assay, immunofluorescence localization, actin inhibitor experiments\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (propeptide binding, functional shedding inhibition, localization), directly establishing enzymatic identity and trafficking\",\n      \"pmids\": [\"16322767\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SUB2 (PfSUB2) is encoded by a single-copy gene and expressed as a large type I integral membrane protein that undergoes extensive post-translational processing; the terminal processing product is expressed in an apical location in merozoites, and SUB2 was proposed as a candidate for the MSP1 maturase based on its subtilisin-like active site and dense granule localization.\",\n      \"method\": \"Gene cloning, Western blot, immunofluorescence/immunoelectron microscopy showing dense granule localization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization by microscopy and post-translational processing demonstrated, but candidate role for MSP1 maturation was not yet experimentally confirmed in this paper\",\n      \"pmids\": [\"10339607\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SUB2 (PfSUB-2) is a second P. falciparum subtilisin-like protein expressed in merozoites as a large type I integral membrane protein that undergoes extensive post-translational processing, with the terminal product in an apical location.\",\n      \"method\": \"Gene identification, Western blot, immunofluorescence localization in merozoites\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct protein characterization and localization by two independent groups (PMID:10339607 and 10551362) with consistent findings\",\n      \"pmids\": [\"10551362\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SUB2 in P. berghei (PbSUB2) is essential for red blood cell invasion; knockout parasites could not be recovered despite successful tagging at the locus, confirming essentiality for the intraerythrocytic cycle. Kinetics of expression and subcellular localization are consistent with a central role in erythrocyte invasion.\",\n      \"method\": \"Gene targeting/knockout attempt in P. berghei, tagging of Pbsub2 locus, immunofluorescence localization\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic essentiality established by failed knockout with successful locus modification as control, replicated concept across species\",\n      \"pmids\": [\"14678331\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}, {\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SUB2 (PfSUB2) sheds PTRAMP (Plasmodium thrombospondin related apical merozoite protein) from the merozoite surface upon erythrocyte invasion, identifying PTRAMP as a substrate of SUB2.\",\n      \"method\": \"Shedding assay, Western blot of surface proteins during invasion\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single study demonstrating SUB2-mediated shedding of a specific substrate; abstract-level detail is limited\",\n      \"pmids\": [\"16879884\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SUB2 (PfSUB2) mediates the secondary (juxtamembrane) processing of MSP1 during erythrocyte invasion; regulated spatiotemporal maturation of MSP1 by SUB2 is essential for parasite growth, as replacement of the secondary processing site with a PfSUB1-sensitive site is deleterious.\",\n      \"method\": \"Targeted homologous recombination to modify MSP1 processing site, parasite growth assay\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-specific mutagenesis of substrate cleavage site via targeted recombination with functional growth readout in a single rigorous study\",\n      \"pmids\": [\"20735778\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SUB2 (PfSUB2) cleaves AMA1 predominantly at a juxtamembrane site; the position of cleavage is determined primarily by distance from the parasite membrane rather than primary sequence. Mutations blocking PfSUB2-mediated shedding could not be stably introduced into the genomic pfama1 locus, establishing that some AMA1 shedding by SUB2 is essential. Parasites expressing shedding-resistant AMA1 show enhanced sensitivity to antibody-mediated invasion inhibition.\",\n      \"method\": \"Targeted homologous recombination, mutagenesis of AMA1 cleavage site, invasion assay, antibody inhibition assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic manipulation of substrate cleavage site with multiple functional readouts (essentiality, antibody sensitivity) in a single rigorous study\",\n      \"pmids\": [\"22194692\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The solution NMR structure of the conserved inhibitory prodomain of SUB2 (PfSUB2) was determined. Despite no detectable sequence homology, the prosub2 domain has structural similarity to bacterial and mammalian subtilisin-like prodomains, suggesting a conserved binding interface with the catalytic domain and providing insight into processing site locations.\",\n      \"method\": \"Solution NMR structure determination of recombinant prosub2 domain\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR structure determined but functional validation of the binding interface was inferred by comparison, not experimentally confirmed in this study\",\n      \"pmids\": [\"23011838\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Trafficking of SUB2 (PfSUB2) to micronemes requires its transmembrane domain; the cytoplasmic domain is essential for surface translocation of the protease to the parasite posterior following discharge from micronemes. Autocatalytic protease activity is required for trafficking of PfSUB2 beyond an early compartment in the secretory pathway. Authentic promoter activity within the intergenic region 5' of the pfsub2 locus is important for correct localization.\",\n      \"method\": \"Truncation/domain-swap constructs, transfection, live-cell imaging, mutagenesis of autocatalytic site\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-specific mutagenesis with multiple functional localization readouts in a single focused study with orthogonal approaches\",\n      \"pmids\": [\"23834729\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SUB2 (PfSUB2) localizes to osmiophilic bodies in P. falciparum female gametocytes, as determined by fluorescent reporter gene fusions and specific antibodies using comparative proteomics of pfg377-disrupted parasites that lack osmiophilic bodies.\",\n      \"method\": \"Comparative label-free proteomics of wild-type vs. pfg377-KO gametocytes, fluorescent reporter fusions, immunofluorescence\",\n      \"journal\": \"Molecular & cellular proteomics : MCP\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — localization established by orthogonal methods (proteomics + reporter fusion + antibody) in a single study, but functional consequence of SUB2 in osmiophilic bodies not determined\",\n      \"pmids\": [\"27432909\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Genetic depletion of SUB2 in P. falciparum abolishes shedding of multiple parasite surface proteins and identifies previously unrecognized substrates. SUB2-null merozoite interaction with RBCs leads to either abortive invasion with rapid RBC lysis, or successful entry but developmental arrest. Selective failure to shed MSP1 reduces intracellular replication, while conditional ablation of the substrate AMA1 produces host RBC lysis. SUB2 activity is critical for host RBC membrane sealing following parasite internalization.\",\n      \"method\": \"Conditional genetic depletion of SUB2, proteomics for substrate identification, live-cell imaging of invasion, electron microscopy\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional knockout with multiple orthogonal readouts (proteomic substrate identification, invasion assays, ultrastructural imaging, substrate-specific conditional lines), rigorous study\",\n      \"pmids\": [\"33287958\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"In P. berghei ookinetes, a SUB2 ortholog (PbSub2) is released during ookinete migration through midgut epithelial cells, suggesting a role for SUB2 in ookinete-stage biology.\",\n      \"method\": \"Immunofluorescence/localization during ookinete midgut invasion\",\n      \"journal\": \"Insect biochemistry and molecular biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single localization observation during ookinete invasion, no functional validation of SUB2 activity at this stage\",\n      \"pmids\": [\"12225921\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"SUB2 (PF3D7_1136900) is an integral membrane subtilisin-like serine protease stored in micronemes that is secreted onto the merozoite surface at egress and translocates actin-dependently to the posterior pole, where it acts as the essential sheddase cleaving multiple surface proteins including MSP1 and AMA1 at juxtamembrane sites; autocatalytic processing is required for secretory pathway trafficking, the transmembrane domain mediates micronemal targeting, and the cytoplasmic domain drives posterior surface translocation; conditional depletion of SUB2 abolishes substrate shedding, causes abortive invasion or developmental arrest, and prevents host RBC membrane sealing, establishing SUB2 as essential for both successful erythrocyte invasion and post-invasion vacuole integrity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SUB2 (PF3D7_1136900) is an essential subtilisin-like serine protease that acts as the merozoite surface sheddase governing erythrocyte invasion in Plasmodium [#0, #10]. Expressed as a single-copy, large type I integral membrane protein that undergoes extensive autocatalytic post-translational processing, SUB2 is stored apically in micronemes and secreted onto the merozoite surface at egress, from where it translocates actin-dependently to the parasite posterior pole [#0, #1, #8]. There it cleaves multiple surface proteins at juxtamembrane positions—including MSP1, AMA1, and PTRAMP—with cleavage site selection determined primarily by distance from the parasite membrane rather than primary sequence [#0, #4, #5, #6]. Its enzymatic identity is established by the SUB2 propeptide, which binds mature parasite-derived SUB2 and selectively inhibits MSP1 and AMA1 shedding [#0, #7]. Trafficking is domain-encoded: autocatalytic activity is required to progress beyond an early secretory compartment, the transmembrane domain directs micronemal targeting, and the cytoplasmic domain drives posterior surface translocation [#8]. SUB2 is genetically essential for the intraerythrocytic cycle in both P. falciparum and P. berghei; conditional depletion abolishes substrate shedding and causes either abortive invasion with RBC lysis or successful entry followed by developmental arrest, and SUB2 activity is required for sealing of the host RBC membrane after internalization [#3, #6, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing that SUB2 exists as a distinct, second subtilisin-like protease of P. falciparum defined the molecular entity and raised the question of its enzymatic role in merozoites.\",\n      \"evidence\": \"Gene cloning, Western blot, and immunofluorescence/immunoelectron microscopy in P. falciparum merozoites by two independent groups\",\n      \"pmids\": [\"10339607\", \"10551362\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzymatic substrate not experimentally confirmed\", \"Proposed MSP1 maturase role remained a hypothesis\", \"Micronemal versus dense-granule assignment not yet resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Detection of a SUB2 ortholog released during ookinete midgut migration hinted that SUB2 function extends beyond the blood-stage merozoite.\",\n      \"evidence\": \"Immunofluorescence localization during P. berghei ookinete invasion of midgut epithelium\",\n      \"pmids\": [\"12225921\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single localization observation with no functional validation\", \"No substrate or phenotype defined at the ookinete stage\", \"Relevance to P. falciparum not addressed\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Genetic knockout attempts answered whether SUB2 is dispensable, establishing its essentiality for the intraerythrocytic cycle.\",\n      \"evidence\": \"Failed gene knockout with successful control tagging of the Pbsub2 locus plus localization in P. berghei/P. yoelii\",\n      \"pmids\": [\"14678331\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of essentiality not defined\", \"Substrates not identified in this study\", \"Does not distinguish an invasion role from other functions\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}, {\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Directly identifying SUB2 as the merozoite surface sheddase resolved its enzymatic identity and placed it in the invasion pathway.\",\n      \"evidence\": \"Recombinant propeptide binding and selective shedding inhibition, immunofluorescence localization, and actin-inhibitor experiments in P. falciparum\",\n      \"pmids\": [\"16322767\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full substrate repertoire not enumerated\", \"Mechanism of actin-dependent posterior translocation not resolved\", \"Cleavage site determinants not defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying PTRAMP as a SUB2 substrate broadened the sheddase's target set beyond MSP1 and AMA1.\",\n      \"evidence\": \"Shedding assay and Western blot of surface proteins during P. falciparum invasion\",\n      \"pmids\": [\"16879884\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-study substrate assignment\", \"Functional consequence of PTRAMP shedding not tested\", \"Cleavage site not mapped\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defining that SUB2 cleaves AMA1 and MSP1 at juxtamembrane sites chosen by membrane distance rather than sequence explained how one protease processes multiple substrates, and confirmed shedding is functionally essential.\",\n      \"evidence\": \"Targeted homologous recombination and cleavage-site mutagenesis of MSP1 and AMA1 with growth, invasion, and antibody-inhibition assays in P. falciparum\",\n      \"pmids\": [\"20735778\", \"22194692\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of distance-based recognition not determined\", \"Interplay between substrates during invasion not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The NMR structure of the SUB2 inhibitory prodomain provided a structural rationale for propeptide-mediated inhibition and processing site placement.\",\n      \"evidence\": \"Solution NMR structure determination of the recombinant prosub2 domain\",\n      \"pmids\": [\"23011838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding interface with the catalytic domain inferred by comparison, not experimentally confirmed\", \"No structure of the mature catalytic domain\", \"No enzyme–substrate complex\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Dissecting SUB2 trafficking assigned specific transport steps to defined protein regions, explaining how the sheddase reaches micronemes and then the posterior surface.\",\n      \"evidence\": \"Truncation/domain-swap constructs, transfection, live-cell imaging, and autocatalytic-site mutagenesis in P. falciparum\",\n      \"pmids\": [\"23834729\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular machinery recognizing the transmembrane and cytoplasmic signals unknown\", \"Mechanistic link between autocatalysis and secretory progression not defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Localizing SUB2 to osmiophilic bodies of female gametocytes indicated a potential transmission-stage compartmentalization distinct from the merozoite microneme.\",\n      \"evidence\": \"Comparative proteomics of pfg377-disrupted gametocytes with fluorescent reporter fusions and immunofluorescence in P. falciparum\",\n      \"pmids\": [\"27432909\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of SUB2 in osmiophilic bodies not determined\", \"No substrate identified at this stage\", \"Relationship to blood-stage sheddase function unclear\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Conditional depletion defined the full phenotypic consequences of losing SUB2, distinguishing invasion, replication, and RBC-sealing roles and expanding its substrate list.\",\n      \"evidence\": \"Conditional genetic depletion of SUB2 with proteomic substrate identification, live-cell invasion imaging, electron microscopy, and substrate-specific conditional lines in P. falciparum\",\n      \"pmids\": [\"33287958\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking shedding to RBC membrane sealing not defined\", \"Identities and roles of newly recognized substrates not fully characterized\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SUB2 achieves its distance-based juxtamembrane cleavage specificity structurally, and what its function is in gametocyte osmiophilic bodies and ookinetes, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of the catalytic domain or an enzyme–substrate complex\", \"No functional assignment of SUB2 at transmission stages\", \"Molecular basis of RBC membrane sealing dependence on SUB2 unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004252\", \"supporting_discovery_ids\": [0, 1, 5, 6]},\n      {\"term_id\": \"GO:0004289\", \"supporting_discovery_ids\": [0, 4, 5, 6, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020009\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0016020\", \"supporting_discovery_ids\": [1, 2, 8]},\n      {\"term_id\": \"GO:0009986\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0020020\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [0, 3, 10]},\n      {\"term_id\": \"GO:0006508\", \"supporting_discovery_ids\": [0, 5, 6, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"MSP1 (substrate)\",\n      \"AMA1 (substrate)\",\n      \"PTRAMP (substrate)\",\n      \"SUB2 propeptide/prodomain (autoinhibitory)\"\n    ],\n    \"other_free_text\": [\n      \"Single-copy gene encoding a large type I integral membrane subtilisin-like serine protease [#1, #2]\",\n      \"Autocatalytic processing required for progression beyond an early secretory compartment; transmembrane domain directs micronemal targeting; cytoplasmic domain drives posterior surface translocation [#8]\",\n      \"Cleaves substrates at juxtamembrane sites selected by distance from the parasite membrane rather than primary sequence [#6]\",\n      \"Genetically essential for the intraerythrocytic cycle in P. falciparum and P. berghei; depletion causes abortive invasion, developmental arrest, and failure of host RBC membrane sealing [#3, #10]\",\n      \"Prodomain NMR structure shows conserved subtilisin prodomain fold despite no detectable sequence homology [#7]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1136900","name":null,"product":"subtilisin-like protease 2","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0911700","name":null,"product":"subtilisin-like protease 2","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0935100","name":null,"product":"subtilisin-like protease 2, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"SUB2","evaluation":null}