{"id":"9631823e-1466-5e19-93bc-205d19055a6d","stable_key":"7fc92b9e-9cbf-556e-8719-6b5244625250:b12-mmad-cys261-co-s","predicate":"coordinates-cobalamin-on","statement":"Human MMADHC donated the Cys261 sulfur ligand to MMACHC-bound cob(II)alamin, forming an interprotein complex that oxidized to thiolato-cob(III)alamin.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"f2acc32e-9316-5a8f-8aee-eac61ea2070f","mechanism_event_label":"A sulfur atom on one chaperone helped hold B12 while it remained bound to the other.","subject":{"id":"c0fe6bd6-68d8-5ab4-a062-e9f4c70f94a3","slug":"mmadhc","display_name":"Human MMADHC / cobalamin-trafficking protein CblD","entity_type_key":"protein"},"object":{"id":"70ae4c83-37b2-5bd7-931d-021cace41eef","slug":"mmachc","display_name":"Human MMACHC / cobalamin-processing protein CblC","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"f2acc32e-9316-5a8f-8aee-eac61ea2070f","stable_key":"7fc92b9e-9cbf-556e-8719-6b5244625250:b12-mmad-cys261-co-s-event","event_type":"biochemical_relationship","label":"A sulfur atom on one chaperone helped hold B12 while it remained bound to the other.","description":"Human MMADHC donated the Cys261 sulfur ligand to MMACHC-bound cob(II)alamin, forming an interprotein complex that oxidized to thiolato-cob(III)alamin.","status":"provisional","compartment":{"slug":"cytosol","display_name":"Cytosol"},"participants":[{"entity":{"id":"fe0ad86e-a233-56c6-94ea-a188d81ce1c0","slug":"cob-ii-alamin","display_name":"Cob(II)alamin","entity_type_key":"small_molecule"},"role":"initial bound cofactor","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"88c49063-bdbd-5fdd-bfe1-da1541c79c8f","slug":"mmachc-mmadhc-cobalamin-complex","display_name":"Human MMACHC–MMADHC cobalamin coordination complex","entity_type_key":"protein_complex"},"role":"coordination product","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"c0fe6bd6-68d8-5ab4-a062-e9f4c70f94a3","slug":"mmadhc","display_name":"Human MMADHC / cobalamin-trafficking protein CblD","entity_type_key":"protein"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"70ae4c83-37b2-5bd7-931d-021cace41eef","slug":"mmachc","display_name":"Human MMACHC / cobalamin-processing protein CblC","entity_type_key":"protein"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"false","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"evidence_location","value_text":"Abstract; indexed Results: CblD binds H2OCbl and forms a complex with CblC","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Human recombinant chaperones; cysteine scanning and EPR/X-ray absorption","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"MMACHC-bound cob(II)alamin mixed with MMADHC; oxygen controls","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Chemical complex formation does not alone prove the complete in-cell route from lysosome to either client enzyme.","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":"A sulfur atom on one chaperone helped hold B12 while it remained bound to the other.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[li-2020-co-s] An Interprotein Co-S Coordination Complex in the B12-Trafficking Pathway (2020). https://pubmed.ncbi.nlm.nih.gov/32871076/ DOI: 10.1021/jacs.0c06590","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Cell-free assay","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"d71b052a-3b7f-52dc-ada4-8fb53ba1c81f","evidence_kind":"source_excerpt","locator":"Lines 879-891","start_line":879,"end_line":891,"excerpt":"### b12-mmad-cys261-co-s\nHuman MMADHC donated the Cys261 sulfur ligand to MMACHC-bound cob(II)alamin, forming an interprotein complex that oxidized to thiolato-cob(III)alamin.\nCondition category: normal\nnutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: A sulfur atom on one chaperone helped hold B12 while it remained bound to the other.\norganism: Homo sapiens\ntissue_or_cell_type: Cell-free assay\nexperimental_model: Human recombinant chaperones; cysteine scanning and EPR/X-ray absorption\nlimitations: Chemical complex formation does not alone prove the complete in-cell route from lysosome to either client enzyme.\nexposure: MMACHC-bound cob(II)alamin mixed with MMADHC; oxygen controls\ncross_nutrient: false\nevidence_location: Abstract; indexed Results: CblD binds H2OCbl and forms a complex with CblC\n[li-2020-co-s] An Interprotein Co-S Coordination Complex in the B12-Trafficking Pathway (2020). https://pubmed.ncbi.nlm.nih.gov/32871076/ DOI: 10.1021/jacs.0c06590","model_system":"Human recombinant chaperones; cysteine scanning and EPR/X-ray absorption","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [li-2020-co-s] An Interprotein Co-S Coordination Complex in the B12-Trafficking Pathway (2020). https://pubmed.ncbi.nlm.nih.gov/32871076/ DOI: 10.1021/jacs.0c06590","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. Not publisher full text.","file_path":"","sha256":"ad5b3a51d36e856aa7fdfd1cc23f690b094689bad87d28e1a621a54675a01c92","revision_id":"118bd616-0c13-549f-bfeb-bc439715b89c","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}