{"gene":"TG_321530","gene_symbol":"CPL","run_date":"2026-09-08T15:15:14","timeline":{"discoveries":[{"year":2009,"finding":"TgCPL is the primary molecular target of the invasion-inhibitory compound LHVS (morpholinurea-leucyl-homophenyl-vinyl sulfone phenyl); a 2.0 Å crystal structure of TgCPL in complex with its propeptide was solved, and targeted disruption of the TgCPL gene in two parasite strains abolished LHVS fluorescent labeling, confirming selectivity.","method":"Crystal structure (2.0 Å resolution), fluorescently labeled LHVS compound, targeted gene disruption in two strains","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus in vitro inhibitor assay plus genetic KO across two strains; multiple orthogonal methods in single rigorous study","pmids":["19596863"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2009,"finding":"TgCPL localizes to a discrete vesicular structure in the apical region of extracellular parasites and to multiple puncta throughout the cytoplasm of intracellular replicating parasites, as shown by fluorescently labeled LHVS and TgCPL-specific antibodies.","method":"Fluorescently labeled LHVS compound, TgCPL-specific antibody immunolocalization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization by two complementary labeling methods in one study, but no functional consequence experimentally linked to the specific localization","pmids":["19596863"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2013,"finding":"TgCPL contributes to proteolytic maturation of proTgM2AP and proTgMIC3, and is associated with the residual body in the parasitophorous vacuole after cell division.","method":"Referenced from prior experimental work (cited in review/vaccine study context)","journal":"BMC infectious diseases","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mechanistic claims cited from prior work without independent experimental validation in this paper; single secondary source","pmids":["23651838"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2014,"finding":"CPL processing in the plant-like vacuole/vacuolar compartment (PLV/VAC) requires acidification; in TgVP1-null mutants, CPL processing was deficient only when V-H+-ATPase was additionally inhibited by bafilomycin A1, indicating that either TgVP1 or TgVATPase is sufficient to support CPL maturation.","method":"Genetic null mutant (TgVP1 KO), pharmacological inhibition (bafilomycin A1), western blot for CPL processing","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO combined with pharmacological epistasis in single lab, two orthogonal approaches","pmids":["24975633"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2020,"finding":"CPL is the dominant protease in a proteolytic hierarchy within the VAC: CPB maturation is dependent on CPL, ASP1 maturation is dependent on CPL, and CPB-deficient and ASP1-deficient parasites show normal protein turnover in the VAC, while CPL ablation causes accumulation of undigested protein and loss of viability during chronic infection.","method":"Genetic ablation of CPB and ASP1 (KO parasites), protein turnover assays in VAC, growth/viability assays in acute and chronic infection stages","journal":"mSphere","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic KOs with defined cellular phenotypes (protein digestion, viability), multiple parasite lines tested, builds on prior CPL KO data","pmids":["32051238"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"finding":"Structure-based design of dipeptidic inhibitors targeting TgCPL active site achieved ~50-fold selectivity for TgCPL over human cathepsin L, with potency improved from 2 µM to 110 nM, validating the TgCPL active site as a druggable target for chronic toxoplasmosis.","method":"Structure-based medicinal chemistry, enzyme inhibition assays (IC50), CNS permeability (brain/plasma ratio)","journal":"Bioorganic & medicinal chemistry letters","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with structure-guided mutagenesis/design, single lab, no independent replication","pmids":["29650289"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"finding":"CPL degrades host-derived cytosolic macromolecules internalized by both tachyzoites and bradyzoites; CPL-deficient parasites accumulate host-expressed mCherry protein within the endolysosomal compartment, demonstrating that CPL is required for digestion of ingested host proteins.","method":"CPL genetic ablation, host-expressed fluorescent reporter (mCherry) accumulation assay, two cystogenic strains (ME49, Pru)","journal":"mSphere","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined biochemical readout (protein accumulation), replicated in two independent cystogenic strains","pmids":["33504659"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"},{"species":"Toxoplasma gondii","strain":"Pru"}]},{"year":2025,"finding":"CPL resides in the PLVAC and degrades host protein cargo delivered via the ingestion pathway; Δcpl mutants show reduced amino acids and glycolytic intermediates and exhibit exacerbated growth defects under amino acid-depleted conditions, demonstrating CPL's role in nutrient scavenging from the host.","method":"Genome-wide CRISPR fitness screen (Δcpl vs WT), bulk metabolomics, growth assays in amino acid-depleted media","journal":"mSphere","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide CRISPR screen combined with metabolomics and targeted growth assays, peer-reviewed publication","pmids":["40172222"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2025,"finding":"Using CPL as a bait protein for TurboID proximity labeling, 9 novel PLVAC-associated proteins were identified, confirming CPL's PLVAC residence and its utility as a marker for this compartment.","method":"TurboID proximity labeling with CPL as bait, mass spectrometry identification of PLVAC-associated proteins","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proximity labeling with defined bait, single lab, no independent replication of PLVAC localization per se but consistent with prior work","pmids":["39864696"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgCPL is a cysteine protease residing in the plant-like vacuolar compartment (PLVAC/VAC) of Toxoplasma gondii that functions as the dominant endolysosomal protease: it matures CPB, ASP1, and micronemal cargo proteins (proTgM2AP, proTgMIC3), degrades host cytosolic macromolecules delivered via the GRA14/ESCRT-driven ingestion pathway to supply amino acids and support parasite metabolism, and is the primary target of the invasion-inhibitory compound LHVS, as established by crystal structure, genetic ablation, metabolomics, and CRISPR fitness screens."},"narrative":{"mechanistic_narrative":"TgCPL is a cysteine protease that acts as the dominant endolysosomal protease of the Toxoplasma gondii plant-like vacuolar compartment (PLVAC/VAC), where it drives proteolytic maturation and bulk protein digestion required for nutrient scavenging and chronic-stage viability [PMID:32051238, PMID:40172222]. It sits at the top of a VAC proteolytic hierarchy, being required for maturation of the downstream proteases CPB and ASP1, such that its ablation—but not that of CPB or ASP1—causes accumulation of undigested protein and loss of viability during chronic infection [PMID:32051238]. CPL degrades host-derived cytosolic macromolecules internalized by both tachyzoites and bradyzoites; in its absence host-expressed reporter protein accumulates within the endolysosomal compartment, and Δcpl parasites show reduced amino acids and glycolytic intermediates and exacerbated growth defects under amino acid depletion, establishing its role in supplying nutrients from the host [PMID:33504659, PMID:40172222]. Its proteolytic maturation depends on acidification of the VAC, supported redundantly by TgVP1 or the V-H+-ATPase [PMID:24975633]. CPL is the primary molecular target of the invasion-inhibitory compound LHVS, and its active site has been validated as a druggable target: a 2.0 Å crystal structure of the CPL–propeptide complex enabled structure-based design of dipeptidic inhibitors with ~50-fold selectivity over human cathepsin L [PMID:19596863, PMID:29650289].","teleology":[{"year":2009,"claim":"Establishing what LHVS actually inhibits was needed to interpret its anti-invasion activity; identifying CPL as the selective target and solving its structure gave a molecular handle on the enzyme.","evidence":"2.0 Å crystal structure of CPL–propeptide complex, fluorescent LHVS labeling, and CPL gene disruption in two strains","pmids":["19596863"],"confidence":"High","gaps":["Cellular substrates not yet defined","Functional consequence of specific subcellular localization not established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2009,"claim":"Locating CPL within the parasite was needed to place its activity in a cellular compartment; labeling showed apical vesicular and cytoplasmic punctate distributions.","evidence":"Fluorescent LHVS labeling and CPL-specific antibody immunolocalization","pmids":["19596863"],"confidence":"Medium","gaps":["Localization not yet functionally linked to any activity","Compartment identity not defined at this stage"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2013,"claim":"Whether CPL processes secretory cargo was addressed by associating it with maturation of proTgM2AP and proTgMIC3 and with the residual body.","evidence":"Claims cited from prior experimental work in a review/vaccine-study context","pmids":["23651838"],"confidence":"Low","gaps":["Cited secondary source without independent experimental validation here","Direct enzyme–substrate relationship not demonstrated in this work"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2014,"claim":"How CPL becomes active was unresolved; showing that its processing requires VAC acidification supported redundantly by TgVP1 or the V-H+-ATPase defined the conditions for its maturation.","evidence":"TgVP1-null mutant combined with bafilomycin A1 inhibition and western blot for CPL processing","pmids":["24975633"],"confidence":"Medium","gaps":["Molecular mechanism of pH-dependent activation not defined","Autocatalytic vs trans-processing not distinguished"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2020,"claim":"The relationship among VAC proteases was unknown; reciprocal knockouts placed CPL at the apex of a proteolytic hierarchy, maturing CPB and ASP1 and being uniquely required for protein turnover and chronic viability.","evidence":"Genetic ablation of CPB and ASP1, VAC protein turnover assays, and viability assays across infection stages","pmids":["32051238"],"confidence":"High","gaps":["Direct cleavage of CPB/ASP1 by CPL not shown biochemically in isolation","Contribution of each downstream protease to specific substrates unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"claim":"Whether CPL digests host-derived material was tested by tracking an ingested host reporter; its accumulation in CPL-deficient parasites established CPL as required for degradation of ingested host proteins.","evidence":"CPL ablation with host-expressed mCherry accumulation assay in two cystogenic strains (ME49, Pru)","pmids":["33504659"],"confidence":"High","gaps":["Full spectrum of host substrates not defined","Delivery route of host cargo to the VAC not fully mapped here"],"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"},{"species":"Toxoplasma gondii","strain":"Pru"}]},{"year":2025,"claim":"The metabolic purpose of host-protein digestion was unclear; combining a genome-wide fitness screen, metabolomics, and amino-acid-depletion growth assays showed CPL supplies amino acids and glycolytic intermediates from the host.","evidence":"Genome-wide CRISPR fitness screen (Δcpl vs WT), bulk metabolomics, and growth in amino acid-depleted media","pmids":["40172222"],"confidence":"High","gaps":["Individual nutrient dependencies not dissected","Coupling between ingestion pathway and CPL activity not mechanistically resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2025,"claim":"Defining the CPL compartment's protein composition was addressed using CPL as a proximity-labeling bait, confirming its PLVAC residence and identifying novel PLVAC-associated proteins.","evidence":"TurboID proximity labeling with CPL bait and mass spectrometry","pmids":["39864696"],"confidence":"Medium","gaps":["Functional roles of identified PLVAC proteins not established","Direct interactions vs mere proximity not distinguished"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The direct enzymatic substrate repertoire of CPL and the mechanism coupling host-cargo delivery to its proteolytic activity remain to be fully defined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No comprehensive substrate map","Mechanism linking ingestion pathway to CPL-mediated digestion not resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["CPB (SUBSTRATE; MATURED BY CPL)","ASP1 (SUBSTRATE; MATURED BY CPL)","PROTGM2AP (SUBSTRATE)","PROTGMIC3 (SUBSTRATE)","TGVP1 / V-H+-ATPASE (ACIDIFICATION SUPPORTING CPL MATURATION)"],"other_free_text":["Primary molecular target of the invasion-inhibitory compound LHVS.","Active site validated as a druggable target with dipeptidic inhibitors ~50-fold selective over human cathepsin L.","Used as a TurboID bait and marker for the PLVAC compartment.","Required for viability during chronic infection and for nutrient scavenging under amino acid depletion."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"19596863","id":"PMC_19596863","title":"Toxoplasma gondii cathepsin L is the primary target of the invasion-inhibitory compound morpholinurea-leucyl-homophenyl-vinyl sulfone phenyl.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19596863","citation_count":54,"is_preprint":false},{"pmid":"24975633","id":"PMC_24975633","title":"A vacuolar-H(+) -pyrophosphatase (TgVP1) is required for microneme secretion, host cell invasion, and extracellular survival of Toxoplasma gondii.","date":"2014","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/24975633","citation_count":53,"is_preprint":false},{"pmid":"23651838","id":"PMC_23651838","title":"Toxoplasma gondii cathepsin proteases are undeveloped prominent vaccine antigens against toxoplasmosis.","date":"2013","source":"BMC infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/23651838","citation_count":24,"is_preprint":false},{"pmid":"32051238","id":"PMC_32051238","title":"Toxoplasma Cathepsin Protease B and Aspartyl Protease 1 Are Dispensable for Endolysosomal Protein Digestion.","date":"2020","source":"mSphere","url":"https://pubmed.ncbi.nlm.nih.gov/32051238","citation_count":17,"is_preprint":false},{"pmid":"29650289","id":"PMC_29650289","title":"Optimization of dipeptidic inhibitors of cathepsin L for improved Toxoplasma gondii selectivity and CNS permeability.","date":"2018","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/29650289","citation_count":15,"is_preprint":false},{"pmid":"33504659","id":"PMC_33504659","title":"Acquisition of Host Cytosolic Protein by Toxoplasma gondii Bradyzoites.","date":"2021","source":"mSphere","url":"https://pubmed.ncbi.nlm.nih.gov/33504659","citation_count":14,"is_preprint":false},{"pmid":"40172222","id":"PMC_40172222","title":"Metabolic adaptability and nutrient scavenging in Toxoplasma gondii: insights from ingestion pathway-deficient mutants.","date":"2025","source":"mSphere","url":"https://pubmed.ncbi.nlm.nih.gov/40172222","citation_count":6,"is_preprint":false},{"pmid":"39864696","id":"PMC_39864696","title":"A novel ENTH domain-containing protein TgTEPSIN is essential for structural maintenance of the plant-like vacuolar compartment and bradyzoite differentiation in toxoplasma gondii.","date":"2025","source":"International journal of biological macromolecules","url":"https://pubmed.ncbi.nlm.nih.gov/39864696","citation_count":1,"is_preprint":false},{"pmid":"39651188","id":"PMC_39651188","title":"Metabolic Adaptability and Nutrient Scavenging in Toxoplasma gondii: Insights from Ingestion Pathway-Deficient Mutants.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/39651188","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7493,"output_tokens":2421,"usd":0.029397,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7924,"output_tokens":3390,"usd":0.062185,"stage2_stop_reason":"end_turn"},"total_usd":0.091582,"stage1_batch_id":"msgbatch_01S6GjoYQm8LTPUsdhASdqag","stage2_batch_id":"msgbatch_01VX63RTMdBJqsG6gQMqoCjz","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"TgCPL is the primary molecular target of the invasion-inhibitory compound LHVS (morpholinurea-leucyl-homophenyl-vinyl sulfone phenyl); a 2.0 Å crystal structure of TgCPL in complex with its propeptide was solved, and targeted disruption of the TgCPL gene in two parasite strains abolished LHVS fluorescent labeling, confirming selectivity.\",\n      \"method\": \"Crystal structure (2.0 Å resolution), fluorescently labeled LHVS compound, targeted gene disruption in two strains\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus in vitro inhibitor assay plus genetic KO across two strains; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"19596863\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TgCPL localizes to a discrete vesicular structure in the apical region of extracellular parasites and to multiple puncta throughout the cytoplasm of intracellular replicating parasites, as shown by fluorescently labeled LHVS and TgCPL-specific antibodies.\",\n      \"method\": \"Fluorescently labeled LHVS compound, TgCPL-specific antibody immunolocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization by two complementary labeling methods in one study, but no functional consequence experimentally linked to the specific localization\",\n      \"pmids\": [\"19596863\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TgCPL contributes to proteolytic maturation of proTgM2AP and proTgMIC3, and is associated with the residual body in the parasitophorous vacuole after cell division.\",\n      \"method\": \"Referenced from prior experimental work (cited in review/vaccine study context)\",\n      \"journal\": \"BMC infectious diseases\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mechanistic claims cited from prior work without independent experimental validation in this paper; single secondary source\",\n      \"pmids\": [\"23651838\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CPL processing in the plant-like vacuole/vacuolar compartment (PLV/VAC) requires acidification; in TgVP1-null mutants, CPL processing was deficient only when V-H+-ATPase was additionally inhibited by bafilomycin A1, indicating that either TgVP1 or TgVATPase is sufficient to support CPL maturation.\",\n      \"method\": \"Genetic null mutant (TgVP1 KO), pharmacological inhibition (bafilomycin A1), western blot for CPL processing\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO combined with pharmacological epistasis in single lab, two orthogonal approaches\",\n      \"pmids\": [\"24975633\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CPL is the dominant protease in a proteolytic hierarchy within the VAC: CPB maturation is dependent on CPL, ASP1 maturation is dependent on CPL, and CPB-deficient and ASP1-deficient parasites show normal protein turnover in the VAC, while CPL ablation causes accumulation of undigested protein and loss of viability during chronic infection.\",\n      \"method\": \"Genetic ablation of CPB and ASP1 (KO parasites), protein turnover assays in VAC, growth/viability assays in acute and chronic infection stages\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic KOs with defined cellular phenotypes (protein digestion, viability), multiple parasite lines tested, builds on prior CPL KO data\",\n      \"pmids\": [\"32051238\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Structure-based design of dipeptidic inhibitors targeting TgCPL active site achieved ~50-fold selectivity for TgCPL over human cathepsin L, with potency improved from 2 µM to 110 nM, validating the TgCPL active site as a druggable target for chronic toxoplasmosis.\",\n      \"method\": \"Structure-based medicinal chemistry, enzyme inhibition assays (IC50), CNS permeability (brain/plasma ratio)\",\n      \"journal\": \"Bioorganic & medicinal chemistry letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with structure-guided mutagenesis/design, single lab, no independent replication\",\n      \"pmids\": [\"29650289\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CPL degrades host-derived cytosolic macromolecules internalized by both tachyzoites and bradyzoites; CPL-deficient parasites accumulate host-expressed mCherry protein within the endolysosomal compartment, demonstrating that CPL is required for digestion of ingested host proteins.\",\n      \"method\": \"CPL genetic ablation, host-expressed fluorescent reporter (mCherry) accumulation assay, two cystogenic strains (ME49, Pru)\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined biochemical readout (protein accumulation), replicated in two independent cystogenic strains\",\n      \"pmids\": [\"33504659\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"},\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Pru\"}\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CPL resides in the PLVAC and degrades host protein cargo delivered via the ingestion pathway; Δcpl mutants show reduced amino acids and glycolytic intermediates and exhibit exacerbated growth defects under amino acid-depleted conditions, demonstrating CPL's role in nutrient scavenging from the host.\",\n      \"method\": \"Genome-wide CRISPR fitness screen (Δcpl vs WT), bulk metabolomics, growth assays in amino acid-depleted media\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide CRISPR screen combined with metabolomics and targeted growth assays, peer-reviewed publication\",\n      \"pmids\": [\"40172222\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Using CPL as a bait protein for TurboID proximity labeling, 9 novel PLVAC-associated proteins were identified, confirming CPL's PLVAC residence and its utility as a marker for this compartment.\",\n      \"method\": \"TurboID proximity labeling with CPL as bait, mass spectrometry identification of PLVAC-associated proteins\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proximity labeling with defined bait, single lab, no independent replication of PLVAC localization per se but consistent with prior work\",\n      \"pmids\": [\"39864696\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    }\n  ],\n  \"current_model\": \"TgCPL is a cysteine protease residing in the plant-like vacuolar compartment (PLVAC/VAC) of Toxoplasma gondii that functions as the dominant endolysosomal protease: it matures CPB, ASP1, and micronemal cargo proteins (proTgM2AP, proTgMIC3), degrades host cytosolic macromolecules delivered via the GRA14/ESCRT-driven ingestion pathway to supply amino acids and support parasite metabolism, and is the primary target of the invasion-inhibitory compound LHVS, as established by crystal structure, genetic ablation, metabolomics, and CRISPR fitness screens.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TgCPL is a cysteine protease that acts as the dominant endolysosomal protease of the Toxoplasma gondii plant-like vacuolar compartment (PLVAC/VAC), where it drives proteolytic maturation and bulk protein digestion required for nutrient scavenging and chronic-stage viability [#4, #7]. It sits at the top of a VAC proteolytic hierarchy, being required for maturation of the downstream proteases CPB and ASP1, such that its ablation—but not that of CPB or ASP1—causes accumulation of undigested protein and loss of viability during chronic infection [#4]. CPL degrades host-derived cytosolic macromolecules internalized by both tachyzoites and bradyzoites; in its absence host-expressed reporter protein accumulates within the endolysosomal compartment, and Δcpl parasites show reduced amino acids and glycolytic intermediates and exacerbated growth defects under amino acid depletion, establishing its role in supplying nutrients from the host [#6, #7]. Its proteolytic maturation depends on acidification of the VAC, supported redundantly by TgVP1 or the V-H+-ATPase [#3]. CPL is the primary molecular target of the invasion-inhibitory compound LHVS, and its active site has been validated as a druggable target: a 2.0 Å crystal structure of the CPL–propeptide complex enabled structure-based design of dipeptidic inhibitors with ~50-fold selectivity over human cathepsin L [#0, #5].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Establishing what LHVS actually inhibits was needed to interpret its anti-invasion activity; identifying CPL as the selective target and solving its structure gave a molecular handle on the enzyme.\",\n      \"evidence\": \"2.0 Å crystal structure of CPL–propeptide complex, fluorescent LHVS labeling, and CPL gene disruption in two strains\",\n      \"pmids\": [\"19596863\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular substrates not yet defined\", \"Functional consequence of specific subcellular localization not established\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Locating CPL within the parasite was needed to place its activity in a cellular compartment; labeling showed apical vesicular and cytoplasmic punctate distributions.\",\n      \"evidence\": \"Fluorescent LHVS labeling and CPL-specific antibody immunolocalization\",\n      \"pmids\": [\"19596863\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Localization not yet functionally linked to any activity\", \"Compartment identity not defined at this stage\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Whether CPL processes secretory cargo was addressed by associating it with maturation of proTgM2AP and proTgMIC3 and with the residual body.\",\n      \"evidence\": \"Claims cited from prior experimental work in a review/vaccine-study context\",\n      \"pmids\": [\"23651838\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Cited secondary source without independent experimental validation here\", \"Direct enzyme–substrate relationship not demonstrated in this work\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"How CPL becomes active was unresolved; showing that its processing requires VAC acidification supported redundantly by TgVP1 or the V-H+-ATPase defined the conditions for its maturation.\",\n      \"evidence\": \"TgVP1-null mutant combined with bafilomycin A1 inhibition and western blot for CPL processing\",\n      \"pmids\": [\"24975633\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of pH-dependent activation not defined\", \"Autocatalytic vs trans-processing not distinguished\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The relationship among VAC proteases was unknown; reciprocal knockouts placed CPL at the apex of a proteolytic hierarchy, maturing CPB and ASP1 and being uniquely required for protein turnover and chronic viability.\",\n      \"evidence\": \"Genetic ablation of CPB and ASP1, VAC protein turnover assays, and viability assays across infection stages\",\n      \"pmids\": [\"32051238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct cleavage of CPB/ASP1 by CPL not shown biochemically in isolation\", \"Contribution of each downstream protease to specific substrates unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Whether CPL digests host-derived material was tested by tracking an ingested host reporter; its accumulation in CPL-deficient parasites established CPL as required for degradation of ingested host proteins.\",\n      \"evidence\": \"CPL ablation with host-expressed mCherry accumulation assay in two cystogenic strains (ME49, Pru)\",\n      \"pmids\": [\"33504659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full spectrum of host substrates not defined\", \"Delivery route of host cargo to the VAC not fully mapped here\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}, {\"species\": \"Toxoplasma gondii\", \"strain\": \"Pru\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The metabolic purpose of host-protein digestion was unclear; combining a genome-wide fitness screen, metabolomics, and amino-acid-depletion growth assays showed CPL supplies amino acids and glycolytic intermediates from the host.\",\n      \"evidence\": \"Genome-wide CRISPR fitness screen (Δcpl vs WT), bulk metabolomics, and growth in amino acid-depleted media\",\n      \"pmids\": [\"40172222\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual nutrient dependencies not dissected\", \"Coupling between ingestion pathway and CPL activity not mechanistically resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defining the CPL compartment's protein composition was addressed using CPL as a proximity-labeling bait, confirming its PLVAC residence and identifying novel PLVAC-associated proteins.\",\n      \"evidence\": \"TurboID proximity labeling with CPL bait and mass spectrometry\",\n      \"pmids\": [\"39864696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional roles of identified PLVAC proteins not established\", \"Direct interactions vs mere proximity not distinguished\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct enzymatic substrate repertoire of CPL and the mechanism coupling host-cargo delivery to its proteolytic activity remain to be fully defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No comprehensive substrate map\", \"Mechanism linking ingestion pathway to CPL-mediated digestion not resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004197\", \"supporting_discovery_ids\": [0, 4, 5, 6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0016485\", \"supporting_discovery_ids\": [2, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [6, 7, 8], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006508\", \"supporting_discovery_ids\": [4, 6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0015031\", \"supporting_discovery_ids\": [6, 7], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}, {\"species\": \"Toxoplasma gondii\", \"strain\": \"Pru\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CPB (substrate; matured by CPL)\",\n      \"ASP1 (substrate; matured by CPL)\",\n      \"proTgM2AP (substrate)\",\n      \"proTgMIC3 (substrate)\",\n      \"TgVP1 / V-H+-ATPase (acidification supporting CPL maturation)\"\n    ],\n    \"other_free_text\": [\n      \"Primary molecular target of the invasion-inhibitory compound LHVS.\",\n      \"Active site validated as a druggable target with dipeptidic inhibitors ~50-fold selective over human cathepsin L.\",\n      \"Used as a TurboID bait and marker for the PLVAC compartment.\",\n      \"Required for viability during chronic infection and for nutrient scavenging under amino acid depletion.\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_321530","name":"CPL","product":"cathepsin CPL","uniprot_acc":"A0A125YST9","chromosome":"TGME49_chrIb","start_pos":1751620},{"strain":"GT1","gene_id":"TGGT1_321530","name":null,"product":"cathepsin CPL","uniprot_acc":null,"chromosome":"TGGT1_chrIb","start_pos":1759925},{"strain":"RH88","gene_id":"TGRH88_020940","name":null,"product":"cathepsin CPL","uniprot_acc":null,"chromosome":"CM023082","start_pos":212065},{"strain":"VEG","gene_id":"TGVEG_321530","name":null,"product":"cathepsin CPL","uniprot_acc":"A0A0F7US01","chromosome":"TGVEG_chrIb","start_pos":1770802}]}