{"id":"a2a1cff0-a227-53af-aa95-6cf71eb189dd","stable_key":"548ab9d6-3a9b-5bed-879c-17d03813b636:b2-met-human-etf-fad-heterodimer","predicate":"binds-cofactor","statement":"Human ETF crystal structure places its single FAD in a cleft shared by ETFA and ETFB, with most FAD contacts in the alpha-chain C-terminal region.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"cf68b7c6-ad10-501b-97d9-d96016d43aa5","mechanism_event_label":"ETF is a two-protein electron shuttle carrying one B2-derived cofactor.","subject":{"id":"8851f7f6-96e8-534d-ba5f-d3eab68eb3db","slug":"electron-transfer-flavoprotein","display_name":"Human electron transfer flavoprotein / ETF","entity_type_key":"protein_complex"},"object":{"id":"e2cd7179-f218-54e8-9ce9-7a836ae35fac","slug":"fad","display_name":"FAD","entity_type_key":"small_molecule"},"evidence_count":1,"mechanism_event":{"id":"cf68b7c6-ad10-501b-97d9-d96016d43aa5","stable_key":"548ab9d6-3a9b-5bed-879c-17d03813b636:b2-met-human-etf-fad-heterodimer-event","event_type":"biochemical_relationship","label":"ETF is a two-protein electron shuttle carrying one B2-derived cofactor.","description":"Human ETF crystal structure places its single FAD in a cleft shared by ETFA and ETFB, with most FAD contacts in the alpha-chain C-terminal region.","status":"provisional","compartment":{"slug":"mitochondria","display_name":"Mitochondria"},"participants":[{"entity":{"id":"949ab4a0-5377-5106-9ca4-6077d83bf31b","slug":"etfa","display_name":"Human electron transfer flavoprotein alpha / ETFA","entity_type_key":"protein"},"role":"alpha subunit","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"2c78956f-60c1-5351-91eb-67abc16b46a2","slug":"etfb","display_name":"Human electron transfer flavoprotein beta / ETFB","entity_type_key":"protein"},"role":"beta subunit","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"8851f7f6-96e8-534d-ba5f-d3eab68eb3db","slug":"electron-transfer-flavoprotein","display_name":"Human electron transfer flavoprotein / ETF","entity_type_key":"protein_complex"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"e2cd7179-f218-54e8-9ce9-7a836ae35fac","slug":"fad","display_name":"FAD","entity_type_key":"small_molecule"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""}]},"contexts":[{"dimension":"evidence_spans","value_text":"[{\"source_bundle\": \"artifacts/riboflavin_metabolism_sources.json\", \"source_key\": \"PMC26136\", \"locator\": \"HTML article p\", \"paragraph_index\": 30, \"char_start\": 0, \"char_end\": 1354, \"evidence_access\": \"full-text\"}]","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Recombinant human ETFA/ETFB expressed in E. coli and crystallized at 2.1 Angstrom resolution.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"No nutrient intervention; structural or biochemical characterization.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Static structure; not a measurement of cellular cofactor availability.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Riboflavin research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"riboflavin","display_name":"Riboflavin (vitamin B2)","entity_type_key":"small_molecule"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"ETF is a two-protein electron shuttle carrying one B2-derived cofactor.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[roberts-1996-human-etf] Three-dimensional structure of human electron transfer flavoprotein to 2.1-A resolution (1996). https://pubmed.ncbi.nlm.nih.gov/8962055/ DOI: 10.1073/pnas.93.25.14355","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Recombinant protein expressed in E. coli","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"80982ec9-5efc-5242-8d25-57e06a2ee838","evidence_kind":"source_excerpt","locator":"Lines 728-739","start_line":728,"end_line":739,"excerpt":"### b2-met-human-etf-fad-heterodimer\nHuman ETF crystal structure places its single FAD in a cleft shared by ETFA and ETFB, with most FAD contacts in the alpha-chain C-terminal region.\nCondition category: normal\nnutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: ETF is a two-protein electron shuttle carrying one B2-derived cofactor.\norganism: Homo sapiens\ntissue_or_cell_type: Recombinant protein expressed in E. coli\nexperimental_model: Recombinant human ETFA/ETFB expressed in E. coli and crystallized at 2.1 Angstrom resolution.\nlimitations: Static structure; not a measurement of cellular cofactor availability.\nexposure: No nutrient intervention; structural or biochemical characterization.\nevidence_spans: [{\"source_bundle\": \"artifacts/riboflavin_metabolism_sources.json\", \"source_key\": \"PMC26136\", \"locator\": \"HTML article p\", \"paragraph_index\": 30, \"char_start\": 0, \"char_end\": 1354, \"evidence_access\": \"full-text\"}]\n[roberts-1996-human-etf] Three-dimensional structure of human electron transfer flavoprotein to 2.1-A resolution (1996). https://pubmed.ncbi.nlm.nih.gov/8962055/ DOI: 10.1073/pnas.93.25.14355","model_system":"Recombinant human ETFA/ETFB expressed in E. coli and crystallized at 2.1 Angstrom resolution.","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [roberts-1996-human-etf] Three-dimensional structure of human electron transfer flavoprotein to 2.1-A resolution (1996). https://pubmed.ncbi.nlm.nih.gov/8962055/ DOI: 10.1073/pnas.93.25.14355","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"4f7c9578-82bf-5e2d-b5c4-72a79fb4f6af","stable_key":"import-548ab9d6-3a9b-5bed-879c-17d03813b636","title":"Riboflavin: mechanisms, deficiency and nutrient interactions (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":"680cb6bc8249877f2410f551807f10d390fdd719014137d7414ba3420e29228d","revision_id":"7a61e299-908d-5372-860b-99ed190f9d7a","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}