{"id":"47d3825b-dc70-58aa-90db-0c26fb309daa","stable_key":"649e861b-265a-5912-bc36-3a73e53ef892:l-serine-psph-metal","predicate":"supports_catalysis_by","statement":"Human PSPH uses an active-site Mg2+ ion; replacing it with Ca2+ changes coordination of catalytic Asp20 in a way that impedes nucleophilic attack.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"c58bf48d-17e6-5c53-ba74-05b921b713d1","mechanism_event_label":"Two minerals can bind differently to the same enzyme.","subject":{"id":"bff427ab-35f9-59c2-bb24-fd5953bbaec2","slug":"magnesium-ion","display_name":"Mg2+","entity_type_key":"ion"},"object":{"id":"1177919d-d7f4-5272-b40c-444f5dbee4d2","slug":"psph","display_name":"Human phosphoserine phosphatase / PSPH","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"c58bf48d-17e6-5c53-ba74-05b921b713d1","stable_key":"649e861b-265a-5912-bc36-3a73e53ef892:l-serine-psph-metal-event","event_type":"observed_relationship","label":"Two minerals can bind differently to the same enzyme.","description":"Human PSPH uses an active-site Mg2+ ion; replacing it with Ca2+ changes coordination of catalytic Asp20 in a way that impedes nucleophilic attack.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"bff427ab-35f9-59c2-bb24-fd5953bbaec2","slug":"magnesium-ion","display_name":"Mg2+","entity_type_key":"ion"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"1177919d-d7f4-5272-b40c-444f5dbee4d2","slug":"psph","display_name":"Human phosphoserine phosphatase / PSPH","entity_type_key":"protein"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"c882cd0b-9d83-5b07-bd1c-fe4d45657dcb","slug":"l-serine","display_name":"L-Serine","entity_type_key":"small_molecule"},"role":"context_participant","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":"context_participant","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"f8d93623-1546-5bb5-a8a8-55761070bf49","slug":"o-phospho-l-serine","display_name":"O-Phospho-L-serine, free metabolite","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"evidence_access","value_text":"Primary abstract","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Human enzyme crystallography; the calcium-bound structure used 0.7 M CaCl2 crystallization conditions.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"The high-calcium structure does not establish inhibition by normal dietary calcium.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"L-Serine collection; species, compartment, exposure, co-substrates and manipulation remain explicit.","comparator":null,"unit":null,"notes":"","entity":{"slug":"l-serine","display_name":"L-Serine","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"Two minerals can bind differently to the same enzyme.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"How calcium inhibits the magnesium-dependent enzyme human phosphoserine phosphatase. · 2004 · https://pubmed.ncbi.nlm.nih.gov/15291819/ · DOI 10.1111/j.0014-2956.2004.04277.x","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"6785beb8-c995-550c-8d60-889123dc32b8","evidence_kind":"source_excerpt","locator":"Lines 54-60","start_line":54,"end_line":60,"excerpt":"## l-serine-psph-metal\nTwo minerals can bind differently to the same enzyme.\nHuman PSPH uses an active-site Mg2+ ion; replacing it with Ca2+ changes coordination of catalytic Asp20 in a way that impedes nucleophilic attack.\nModel: Human enzyme crystallography; the calcium-bound structure used 0.7 M CaCl2 crystallization conditions.\nLimitations: The high-calcium structure does not establish inhibition by normal dietary calcium.\nEvidence access: Primary abstract\nHow calcium inhibits the magnesium-dependent enzyme human phosphoserine phosphatase. · 2004 · https://pubmed.ncbi.nlm.nih.gov/15291819/ · DOI 10.1111/j.0014-2956.2004.04277.x","model_system":"Human enzyme crystallography; the calcium-bound structure used 0.7 M CaCl2 crystallization conditions.","directness":"reported_statement","verification_status":"source_derived_draft","notes":"Original curation paraphrase; evidence access and experimental limitations specified.","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"70bcf57a-36bb-563f-9073-2d616e5f155a","stable_key":"import-649e861b-265a-5912-bc36-3a73e53ef892","title":"L-Serine: synthesis, one-carbon metabolism, lipids and cross-nutrient mechanisms (2026-09-19)","document_type":"imported_text","citation_label":"AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text.","file_path":"","sha256":"22a750ce2b94f8607268c58322c48c4f0468f403b72a4008307538a6e5ff86d5","revision_id":"c1d6a7e1-9558-5bc6-9e3b-7080c26d3dbc","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}