{"id":"cf2f9162-0946-5d92-a1db-d4272d0de89a","stable_key":"cfa4bd86-d88d-555a-975c-68877bf00e0f:lutein-bco2-mature-active","predicate":"supports","statement":"Removing the mitochondrial targeting sequence improved human BCO2a solubility and enabled carotenoid-cleavage activity.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"6e946015-85b2-5cb5-b296-9dfa3c45f51d","mechanism_event_label":"Processing and expression conditions revealed active human enzyme.","subject":{"id":"3d1f01e1-56d2-58f3-85b7-b85743824258","slug":"human-bco2a-mts-removed","display_name":"Human BCO2a with mitochondrial targeting sequence removed","entity_type_key":"protein_state"},"object":{"id":"9d4c2464-5f85-5778-a94b-52164550998d","slug":"human-bco2-carotenoid-cleavage","display_name":"Human BCO2 carotenoid cleavage activity","entity_type_key":"cellular_process"},"evidence_count":1,"mechanism_event":{"id":"6e946015-85b2-5cb5-b296-9dfa3c45f51d","stable_key":"cfa4bd86-d88d-555a-975c-68877bf00e0f:lutein-bco2-mature-active-event","event_type":"biochemical_relationship","label":"Processing and expression conditions revealed active human enzyme.","description":"Removing the mitochondrial targeting sequence improved human BCO2a solubility and enabled carotenoid-cleavage activity.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"3d1f01e1-56d2-58f3-85b7-b85743824258","slug":"human-bco2a-mts-removed","display_name":"Human BCO2a with mitochondrial targeting sequence removed","entity_type_key":"protein_state"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"9d4c2464-5f85-5778-a94b-52164550998d","slug":"human-bco2-carotenoid-cleavage","display_name":"Human BCO2 carotenoid cleavage activity","entity_type_key":"cellular_process"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""}]},"contexts":[{"dimension":"evidence_span","value_text":"{\"source_cache\": \"artifacts/lutein-research/32873706.abstract.txt\", \"locator\": \"Primary indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"1555914c4a5090c968595f2aba72ce276054594a66423916be600a600a28349f\", \"start_char\": 0, \"end_char\": 1517, \"text_sha256\": \"1555914c4a5090c968595f2aba72ce276054594a66423916be600a600a28349f\"}","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Isoform targeting, recombinant expression and enzyme assays","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Removal of N-terminal mitochondrial targeting sequence; expression optimization","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Activity of processed recombinant protein does not quantify retinal flux; mouse chimeric substrate results remain mouse-specific.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Lutein research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"lutein","display_name":"Lutein","entity_type_key":"small_molecule"}},{"dimension":"organism","value_text":"Human BCO2 isoforms and engineered mouse protein","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"Processing and expression conditions revealed active human enzyme.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[lutein-p32873706] The human mitochondrial enzyme BCO2 exhibits catalytic activity toward carotenoids and apocarotenoids. (2020). https://pubmed.ncbi.nlm.nih.gov/32873706/ DOI: 10.1074/jbc.ra120.015515","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"ARPE-19 cells and bacterial expression","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"cd076e93-e2f7-5672-8221-8b6daddfe7d2","evidence_kind":"source_excerpt","locator":"Lines 281-292","start_line":281,"end_line":292,"excerpt":"### lutein-bco2-mature-active\nRemoving the mitochondrial targeting sequence improved human BCO2a solubility and enabled carotenoid-cleavage activity.\nCondition category: normal\nnutrient_topic: Lutein research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Processing and expression conditions revealed active human enzyme.\norganism: Human BCO2 isoforms and engineered mouse protein\ntissue_or_cell_type: ARPE-19 cells and bacterial expression\nexperimental_model: Isoform targeting, recombinant expression and enzyme assays\nlimitations: Activity of processed recombinant protein does not quantify retinal flux; mouse chimeric substrate results remain mouse-specific.\nexposure: Removal of N-terminal mitochondrial targeting sequence; expression optimization\nevidence_span: {\"source_cache\": \"artifacts/lutein-research/32873706.abstract.txt\", \"locator\": \"Primary indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"1555914c4a5090c968595f2aba72ce276054594a66423916be600a600a28349f\", \"start_char\": 0, \"end_char\": 1517, \"text_sha256\": \"1555914c4a5090c968595f2aba72ce276054594a66423916be600a600a28349f\"}\n[lutein-p32873706] The human mitochondrial enzyme BCO2 exhibits catalytic activity toward carotenoids and apocarotenoids. (2020). https://pubmed.ncbi.nlm.nih.gov/32873706/ DOI: 10.1074/jbc.ra120.015515","model_system":"Isoform targeting, recombinant expression and enzyme assays","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [lutein-p32873706] The human mitochondrial enzyme BCO2 exhibits catalytic activity toward carotenoids and apocarotenoids. (2020). https://pubmed.ncbi.nlm.nih.gov/32873706/ DOI: 10.1074/jbc.ra120.015515","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"beef4241-6ebd-5b36-864c-6ef3ed7e61b8","stable_key":"import-cfa4bd86-d88d-555a-975c-68877bf00e0f","title":"Lutein: metabolism, signaling and nutrient connections (2026-09-17)","document_type":"imported_text","citation_label":"AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text.","file_path":"","sha256":"1514ec459913a7044b4c4e1012ed367bcb918298181ebabd2a9e2ccecd789053","revision_id":"bae2c856-0785-546f-b08f-869318c27f9e","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[{"id":"dac36506-0124-5e66-8730-d84782ea605b","title":"Is human BCO2 inactive, or does its preparation conceal activity?","kind":"qualification","status":"open","why":"The 2014 paper interpreted absent activity as human BCO2 inactivity explaining macular pigment retention. Later primary papers explicitly challenged that general conclusion and demonstrated activity after changes to targeting-sequence processing, expression and assay conditions. This is a published mechanistic disagreement, not a correction to ledger prose.","resolution":"The blanket claim that human BCO2 is catalytically inactive is not supported by the later evidence. Preserve the original negative assay and the demonstrated effects of protein processing and preparation. Human retinal cleavage rates and the contribution to selective pigment retention remain unresolved; the 2025 expression study adds regional and mitochondrial context.","created_at":"2026-09-18 03:35:38","record_type":"conflict","display_label":"Recorded conflict","record_url":"/conflicts/dac36506-0124-5e66-8730-d84782ea605b","sides":[{"conflict_id":"dac36506-0124-5e66-8730-d84782ea605b","ordinal":0,"label":"One early assay found no detectable human enzyme activity.","revision_id":"bae2c856-0785-546f-b08f-869318c27f9e","start_line":255,"end_line":266,"quote":"### lutein-bco2-2014-inactive\nThe 2014 expression assay detected zeaxanthin cleavage by mouse BCO2 but not human BCO2.\nCondition category: normal\nnutrient_topic: Lutein research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: One early assay found no detectable human enzyme activity.\norganism: Human and mouse proteins; bacterial expression\ntissue_or_cell_type: Recombinant BCO2 and retina\nexperimental_model: Recombinant enzyme expression and comparative binding\nlimitations: Historical assay result; later work demonstrates human catalytic competence with altered protein processing and expression conditions.\nexposure: Zeaxanthin-producing bacteria; surface plasmon resonance\nevidence_span: {\"source_cache\": \"artifacts/lutein-research/24982131.abstract.txt\", \"locator\": \"Primary indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"975bef59c81c57ad6e18b45581b23174165732965e8d7e017275fe98ca3ab4a0\", \"start_char\": 0, \"end_char\": 1743, \"text_sha256\": \"975bef59c81c57ad6e18b45581b23174165732965e8d7e017275fe98ca3ab4a0\"}\n[lutein-p24982131] Inactivity of human β,β-carotene-9',10'-dioxygenase (BCO2) underlies retinal accumulation of the human macular carotenoid pigment. (2014). https://pubmed.ncbi.nlm.nih.gov/24982131/ DOI: 10.1073/pnas.1402526111","source_key":"import-cfa4bd86-d88d-555a-975c-68877bf00e0f","source_title":"Lutein: metabolism, signaling and nutrient connections (2026-09-17)","claim_ids":["9b0500c8-5f88-5e2a-89e4-5f3ee42064b2"]},{"conflict_id":"dac36506-0124-5e66-8730-d84782ea605b","ordinal":1,"label":"Processing and expression conditions revealed active human enzyme.","revision_id":"bae2c856-0785-546f-b08f-869318c27f9e","start_line":281,"end_line":292,"quote":"### lutein-bco2-mature-active\nRemoving the mitochondrial targeting sequence improved human BCO2a solubility and enabled carotenoid-cleavage activity.\nCondition category: normal\nnutrient_topic: Lutein research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Processing and expression conditions revealed active human enzyme.\norganism: Human BCO2 isoforms and engineered mouse protein\ntissue_or_cell_type: ARPE-19 cells and bacterial expression\nexperimental_model: Isoform targeting, recombinant expression and enzyme assays\nlimitations: Activity of processed recombinant protein does not quantify retinal flux; mouse chimeric substrate results remain mouse-specific.\nexposure: Removal of N-terminal mitochondrial targeting sequence; expression optimization\nevidence_span: {\"source_cache\": \"artifacts/lutein-research/32873706.abstract.txt\", \"locator\": \"Primary indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"1555914c4a5090c968595f2aba72ce276054594a66423916be600a600a28349f\", \"start_char\": 0, \"end_char\": 1517, \"text_sha256\": \"1555914c4a5090c968595f2aba72ce276054594a66423916be600a600a28349f\"}\n[lutein-p32873706] The human mitochondrial enzyme BCO2 exhibits catalytic activity toward carotenoids and apocarotenoids. (2020). https://pubmed.ncbi.nlm.nih.gov/32873706/ DOI: 10.1074/jbc.ra120.015515","source_key":"import-cfa4bd86-d88d-555a-975c-68877bf00e0f","source_title":"Lutein: metabolism, signaling and nutrient connections (2026-09-17)","claim_ids":["cf2f9162-0946-5d92-a1db-d4272d0de89a"]},{"conflict_id":"dac36506-0124-5e66-8730-d84782ea605b","ordinal":2,"label":"How the protein was prepared changed the measured activity.","revision_id":"bae2c856-0785-546f-b08f-869318c27f9e","start_line":320,"end_line":331,"quote":"### lutein-bco2-method-dependence\nExpression temperature and detergent choice affected recombinant BCO2 binding and xanthophyll turnover, including meso-zeaxanthin.\nCondition category: normal\nnutrient_topic: Lutein research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: How the protein was prepared changed the measured activity.\norganism: Primate and murine BCO2\ntissue_or_cell_type: Protein preparations and human hepatic cell line\nexperimental_model: Comparative recombinant enzyme and cell experiments\nlimitations: Conserved activity does not demonstrate identical rates across species or diets.\nexposure: Low-temperature expression and detergent variation\nevidence_span: {\"source_cache\": \"artifacts/lutein-research/26307071.abstract.txt\", \"locator\": \"Primary indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"6b225e90d2edb66a12583bcdaefb8247cf57c26dffd4f02a1a189907c6f97916\", \"start_char\": 0, \"end_char\": 1495, \"text_sha256\": \"6b225e90d2edb66a12583bcdaefb8247cf57c26dffd4f02a1a189907c6f97916\"}\n[lutein-p26307071] Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism. (2015). https://pubmed.ncbi.nlm.nih.gov/26307071/ DOI: 10.1074/jbc.m115.668822","source_key":"import-cfa4bd86-d88d-555a-975c-68877bf00e0f","source_title":"Lutein: metabolism, signaling and nutrient connections (2026-09-17)","claim_ids":["cb38cb12-0dc6-587a-99ee-965f2706709d"]}]}],"corrections":[],"research":null}