biostudies-literatureHorne CRNational Health and Medical Research CouncilBCJ20253431https://www.ebi.ac.uk/biostudies/studies/S-EPMC12751073biostudies-literatureUnknown482(23)Calmodulin (CaM) serves an essential role in eukaryotic cells as a Ca2+ sensor. Ca2+ binding leads to conformation changes in CaM that enable engagement of a repertoire of enzymes and the regulation of their catalytic activities. Classically, Ca2+-CaM binds to an inhibitory pseudosubstrate sequence C-terminal to the kinase domain in members of the Ca2+-CaM-dependent protein kinase (CAMK) family and relieves inhibition to promote catalytic activity. Here, we report an unexpected mechanism by which CaM can bind CHK2 kinase to inhibit its kinase activity. Using biochemical, biophysical and structural mass spectrometry, we identify a direct interaction of Ca2+-CaM with the CHK2 kinase domain that suppresses CHK2 catalytic activity in vitro and identify K373 in CHK2 as crucial for cell proliferThe Biochemical journalUnconventional binding of calmodulin to CHK2 kinase inhibits catalytic activity.PMC127510731172929, 2034104, 9000719, 2034044, 2001817Horne CRScott JWYoung SNBurke JEPetersen JBelousoff MJVaibhav VManning GDite TASuresh SWang TDavies KADagley LFNyvall HGMurphy JMMeans ARGonzalez Castro AMather LJfalseUnconventional binding of calmodulin to CHK2 kinase inhibits catalytic activity.Calmodulin (CaM) serves an essential role in eukaryotic cells as a Ca2+ sensor. Ca2+ binding leads to conformation changes in CaM that enable engagement of a repertoire of enzymes and the regulation of their catalytic activities. Classically, Ca2+-CaM binds to an inhibitory pseudosubstrate sequence C-terminal to the kinase domain in members of the Ca2+-CaM-dependent protein kinase (CAMK) family and relieves inhibition to promote catalytic activity. Here, we report an unexpected mechanism by which CaM can bind CHK2 kinase to inhibit its kinase activity. Using biochemical, biophysical and structural mass spectrometry, we identify a direct interaction of Ca2+-CaM with the CHK2 kinase domain that suppresses CHK2 catalytic activity in vitro and identify K373 in CHK2 as crucial for cell prolifer2025-01-01T00:00:00Z2025 Dec2026-07-15T11:58:08.282Z2026-07-04T03:12:17.156ZS-EPMC127510734100324210.1042/BCJ20253431