{"id":"da3a82c7-2acc-582e-a890-46f52bece082","stable_key":"434e1e27-eb90-583a-956b-62472726ffba:ca-cardiac-troponin-calcium-switch","predicate":"binds","statement":"Calcium binds the regulatory site of cardiac troponin C; the calcium-loaded ternary structure supports altered inhibitory troponin-I interactions with actin.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"c0d41a93-25bf-5e84-b403-3788b16fdcc7","mechanism_event_label":"Troponin C senses calcium to regulate cardiac contraction.","subject":{"id":"e359bc15-e675-5d83-b0fe-1d70814e130b","slug":"calcium-ion","display_name":"Calcium ion","entity_type_key":"ion"},"object":{"id":"a975904a-af1b-52e5-9f62-4d6efaf1d8a6","slug":"tnnc1","display_name":"Cardiac and slow skeletal troponin C / TNNC1","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"c0d41a93-25bf-5e84-b403-3788b16fdcc7","stable_key":"434e1e27-eb90-583a-956b-62472726ffba:ca-cardiac-troponin-calcium-switch-event","event_type":"binding","label":"Troponin C senses calcium to regulate cardiac contraction.","description":"Calcium binds the regulatory site of cardiac troponin C; the calcium-loaded ternary structure supports altered inhibitory troponin-I interactions with actin.","status":"provisional","compartment":{"slug":"sarcomere","display_name":"Sarcomere"},"participants":[{"entity":{"id":"e359bc15-e675-5d83-b0fe-1d70814e130b","slug":"calcium-ion","display_name":"Calcium ion","entity_type_key":"ion"},"role":"regulatory_ligand","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"a975904a-af1b-52e5-9f62-4d6efaf1d8a6","slug":"tnnc1","display_name":"Cardiac and slow skeletal troponin C / TNNC1","entity_type_key":"protein"},"role":"calcium_sensor","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"055ec4f2-0728-5e2f-b594-1554dadff73b","slug":"tnni3","display_name":"Cardiac troponin I / TNNI3","entity_type_key":"protein"},"role":"inhibitory_subunit","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"07cd7be1-0bc5-591e-8f4c-2698708418c6","slug":"sarcomere","display_name":"Sarcomere","entity_type_key":"organelle"},"role":"experimental_location","stoichiometry":null,"state_label":"","sequence_order":3,"notes":"Study location; presence here is not a separate transport or causal claim."}]},"contexts":[{"dimension":"compartment_description","value_text":"Sarcomeric thin-filament regulatory complex","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Purified human cardiac troponin ternary core; crystallography","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Actin-disengagement is a structural model; this is not a direct whole-heart force measurement or a smooth-muscle mechanism.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Calcium research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"calcium","display_name":"Calcium","entity_type_key":"nutrient_element"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"Troponin C senses calcium to regulate cardiac contraction.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[ca-takeda2003] Structure of the core domain of human cardiac troponin in the Ca2+-saturated form (2003). https://pubmed.ncbi.nlm.nih.gov/12840750/ DOI: 10.1038/nature01780","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"research_relationship_category","value_text":"binding","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Cardiac troponin core","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"c05be805-e38b-5e5e-b69b-caeafa8c0252","evidence_kind":"source_excerpt","locator":"Lines 770-781","start_line":770,"end_line":781,"excerpt":"### ca-cardiac-troponin-calcium-switch\nCalcium binds the regulatory site of cardiac troponin C; the calcium-loaded ternary structure supports altered inhibitory troponin-I interactions with actin.\nCondition category: normal\nnutrient_topic: Calcium research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Troponin C senses calcium to regulate cardiac contraction.\norganism: Homo sapiens\ntissue_or_cell_type: Cardiac troponin core\nexperimental_model: Purified human cardiac troponin ternary core; crystallography\nlimitations: Actin-disengagement is a structural model; this is not a direct whole-heart force measurement or a smooth-muscle mechanism.\nresearch_relationship_category: binding\ncompartment_description: Sarcomeric thin-filament regulatory complex\n[ca-takeda2003] Structure of the core domain of human cardiac troponin in the Ca2+-saturated form (2003). https://pubmed.ncbi.nlm.nih.gov/12840750/ DOI: 10.1038/nature01780","model_system":"Purified human cardiac troponin ternary core; crystallography","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. 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