{"doi":"10.1016/j.jbc.2025.108258","title":"Kinetics insight into the roles of the N- and C-lobes of calmodulin in RyR1 channel regulation","abstract":"Calmodulin (CaM) activates the skeletal muscle Ca 2+ release channel (ryanodine receptor, RyR1) at nanomolar Ca 2+ and inhibits it at micromolar Ca 2+ . CaM conversion from RyR1 activator to inhibitor is due to structural changes induced by Ca 2+ binding at CaM's two lobes. However, it remains unclear which lobe provides the switch for this conversion. Here, we attached the environment-sensitive fluorophore acrylodan (Acr) at either lobe of intact CaM or lobe-specific Ca 2+ -sensitive CaM mutants, and monitored the effects of Ca 2+ binding via the fluorescence change of free or RyR1-bound Acr CaM. Using steady state measurements, we found that Ca 2+ binding to free CaM causes a dramatic structural change in the N-lobe, but only a slight effect on the C-lobe of the Ca 2+ -sensitive lobe-specific mutants, in addition to the previously known higher Ca 2+ affinity at the C-lobe versus the N-lobe. Using stopped-flow measurements, we found ∼30x faster Ca 2+ dissociation from the N- versus C-lobe, and ∼20x slower Ca 2+ association to the N-lobe versus C-lobe. These Ca 2+ binding properties hold for the CaM/RyR1 complex, and Ca 2+ affinity is enhanced at the CaM C-lobe but decreased at the N-lobe by RyR1 binding. We propose that fast Ca 2+ -binding at the C-lobe of CaM initiates its inhibition to RyR1 at high [Ca 2+ ], while slow Ca 2+ binding to the N-lobe is necessary for timely enhancement of the inhibitory effect. The dysregulation of RyR1 by M124Q-CaM may be explained by the lower Ca 2+ affinity versus WT-CaM, as suggested by both steady-state and transient kinetics results.","journal":"Journal of Biological Chemistry","year":2025,"id":551459,"datarank":0.10397207708399181,"base_score":0.6931471805599453,"endowment":0.6931471805599453,"self_citation_contribution":0.10397207708399181,"citation_network_contribution":0.0,"self_endowment_contribution":0.10397207708399181,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":1,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9555,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":794503,"name":"Levy M. Treinen","orcid":null,"position":1,"is_corresponding":false},{"id":1447585,"name":"Skylar J Mast","orcid":null,"position":2,"is_corresponding":false},{"id":442849,"name":"Megan R. McCarthy","orcid":null,"position":3,"is_corresponding":false},{"id":430804,"name":"Bengt Svensson","orcid":"0000-0003-3932-2376","position":4,"is_corresponding":false},{"id":417547,"name":"David D. Thomas","orcid":"0000-0002-8822-2040","position":5,"is_corresponding":false},{"id":417548,"name":"Rǎzvan L. Cornea","orcid":"0000-0001-5739-0992","position":6,"is_corresponding":false},{"id":793960,"name":"Jingyan Zhang","orcid":"0000-0001-6979-0969","position":0,"is_corresponding":true}],"reference_count":58,"raw_metadata":{"citation_network_status":"fetched"},"created_at":"2026-07-19T02:54:25.065895Z","pmid":"39904484","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}