{"id":"a52a315e-9c56-5e80-83d2-52c63efaf030","stable_key":"7fc92b9e-9cbf-556e-8719-6b5244625250:b12-abs-calcium-recognition","predicate":"supports","statement":"In the human IF-cobalamin/CUB5-8 structure, calcium-dependent contacts connect cubilin ligand-binding domains to intrinsic factor, providing a molecular basis for calcium-dependent recognition.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"111b6015-04cc-5b5a-8b90-19caf5f76e18","mechanism_event_label":"Calcium helps intrinsic factor dock with the B12 receptor.","subject":{"id":"e359bc15-e675-5d83-b0fe-1d70814e130b","slug":"calcium-ion","display_name":"Calcium ion","entity_type_key":"ion"},"object":{"id":"514599c6-aab8-5349-9d63-d4383a3da229","slug":"cubn-if-cobalamin-binding","display_name":"Human cubilin binding of intrinsic factor-cobalamin","entity_type_key":"cellular_process"},"evidence_count":1,"mechanism_event":{"id":"111b6015-04cc-5b5a-8b90-19caf5f76e18","stable_key":"7fc92b9e-9cbf-556e-8719-6b5244625250:b12-abs-calcium-recognition-event","event_type":"biochemical_relationship","label":"Calcium helps intrinsic factor dock with the B12 receptor.","description":"In the human IF-cobalamin/CUB5-8 structure, calcium-dependent contacts connect cubilin ligand-binding domains to intrinsic factor, providing a molecular basis for calcium-dependent recognition.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"b6d9b937-895d-5e0a-8cc5-0454a0b7d373","slug":"vitamin-b12","display_name":"Vitamin B12 (cobalamins)","entity_type_key":"chemical_species"},"role":"nutrient","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"7a3dab53-fbcd-58da-9942-21f1a3ed088d","slug":"cubn","display_name":"Human cubilin / CUBN","entity_type_key":"protein"},"role":"receptor","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"490161eb-b7f8-56b6-82bc-77c8c0bdc1ca","slug":"gif","display_name":"Human gastric intrinsic factor / GIF","entity_type_key":"protein"},"role":"ligand-carrier","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"e359bc15-e675-5d83-b0fe-1d70814e130b","slug":"calcium-ion","display_name":"Calcium ion","entity_type_key":"ion"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"514599c6-aab8-5349-9d63-d4383a3da229","slug":"cubn-if-cobalamin-binding","display_name":"Human cubilin binding of intrinsic factor-cobalamin","entity_type_key":"cellular_process"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"true","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Recombinant human proteins; crystal complex at 3.3 angstrom","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Purified complex containing calcium ions","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Does not define a dietary calcium intake target or prove nutritional calcium deficiency causes B12 malabsorption.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"vitamin-b12","display_name":"Vitamin B12 (cobalamins)","entity_type_key":"chemical_species"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"Calcium helps intrinsic factor dock with the B12 receptor.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[andersen-2010-if-cubn] Structural basis for receptor recognition of vitamin-B(12)-intrinsic factor complexes. (2010). https://pubmed.ncbi.nlm.nih.gov/20237569/ DOI: 10.1038/nature08874","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Extracellular ileal receptor binding site","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"dae4547d-39d7-5d20-9501-4f06389cebfd","evidence_kind":"source_excerpt","locator":"Lines 257-268","start_line":257,"end_line":268,"excerpt":"### b12-abs-calcium-recognition\nIn the human IF-cobalamin/CUB5-8 structure, calcium-dependent contacts connect cubilin ligand-binding domains to intrinsic factor, providing a molecular basis for calcium-dependent recognition.\nCondition category: normal\nnutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Calcium helps intrinsic factor dock with the B12 receptor.\norganism: Homo sapiens\ntissue_or_cell_type: Extracellular ileal receptor binding site\nexperimental_model: Recombinant human proteins; crystal complex at 3.3 angstrom\nlimitations: Does not define a dietary calcium intake target or prove nutritional calcium deficiency causes B12 malabsorption.\nexposure: Purified complex containing calcium ions\ncross_nutrient: true\n[andersen-2010-if-cubn] Structural basis for receptor recognition of vitamin-B(12)-intrinsic factor complexes. (2010). https://pubmed.ncbi.nlm.nih.gov/20237569/ DOI: 10.1038/nature08874","model_system":"Recombinant human proteins; crystal complex at 3.3 angstrom","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [andersen-2010-if-cubn] Structural basis for receptor recognition of vitamin-B(12)-intrinsic factor complexes. (2010). https://pubmed.ncbi.nlm.nih.gov/20237569/ DOI: 10.1038/nature08874","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"73145023-2982-5848-aff2-8d8875d6b9c5","stable_key":"import-7fc92b9e-9cbf-556e-8719-6b5244625250","title":"Vitamin B12: 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. 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