biostudies-literature00460Sondergaard MTAlberta InnovatesNovo NordiskNHLBI NIH HHSNational Institutes of HealthLundbeckfondenNovo Nordisk FondenLundbeck FoundationNIGMS NIH HHSCIHRDet Frie Forskningsråd1385-1395https://www.ebi.ac.uk/biostudies/studies/S-EPMC5270481biostudies-literatureUnknown292(4)A number of point mutations in the intracellular Ca²⁺-sensing protein calmodulin (CaM) are arrhythmogenic, yet their underlying mechanisms are not clear. These mutations generally decrease Ca²⁺ binding to CaM and impair inhibition of CaM-regulated Ca²⁺ channels like the cardiac Ca²⁺ release channel (ryanodine receptor, RyR2), and it appears that attenuated CaM Ca²⁺ binding correlates with impaired CaM-dependent RyR2 inhibition. Here, we investigated the RyR2 inhibitory action of the CaM p.Phe142Leu mutation (F142L; numbered including the start-Met), which markedly reduces CaM Ca²⁺ binding. Surprisingly, CaM-F142L had little to no aberrant effect on RyR2-mediated store overload-induced Ca²⁺ release in HEK293 cells compared with CaM-WT. Furthermore, CaM-F142L enhanced CaM-dependent RyR2 inhibition at the single channel level compared with CaM-WT. This is in stark contrast to the actions of arrhythmogenic CaM mutations N54I, D96V, N98S, and D130G, which all diminish CaM-dependent RyR2 inhibition. Thermodynamic analysis showed that apoCaM-F142L converts an endothermal interaction between CaM and the CaM-binding domain (CaMBD) of RyR2 into an exothermal one. Moreover, NMR spectra revealed that the CaM-F142L-CaMBD interaction is structurally different from that of CaM-WT at low Ca²⁺ These data indicate a distinct interaction between CaM-F142L and the RyR2 CaMBD, which may explain the stronger CaM-dependent RyR2 inhibition by CaM-F142L, despite its reduced Ca²⁺ binding. Collectively, these results add to our understanding of CaM-dependent regulation of RyR2 as well as the mechanistic effects of arrhythmogenic CaM mutations. The unique properties of the CaM-F142L mutation may provide novel clues on how to suppress excessive RyR2 Ca²⁺ release by manipulating the CaM-RyR2 interaction.The Journal of biological chemistryThe Arrhythmogenic Calmodulin p.Phe142Leu Mutation Impairs C-domain Ca2+ Binding but Not Calmodulin-dependent Inhibition of the Cardiac Ryanodine Receptor.PMC52704812013–14432HL057832DFF-4093–00242DFF-4181–00447NNF15OC0017762R01 HL057832AR054098201400104NNF16OC0023344R151-2013-14432R01 GM111397NNF15OC001776299Liu YLarsen KTWang RWimmer RVan Petegem FTian XHolt CChen SRSondergaard MTNani AFill MOvergaard MT46falseThe Arrhythmogenic Calmodulin p.Phe142Leu Mutation Impairs C-domain Ca2+ Binding but Not Calmodulin-dependent Inhibition of the Cardiac Ryanodine Receptor.A number of point mutations in the intracellular Ca²⁺-sensing protein calmodulin (CaM) are arrhythmogenic, yet their underlying mechanisms are not clear. These mutations generally decrease Ca²⁺ binding to CaM and impair inhibition of CaM-regulated Ca²⁺ channels like the cardiac Ca²⁺ release channel (ryanodine receptor, RyR2), and it appears that attenuated CaM Ca²⁺ binding correlates with impaired CaM-dependent RyR2 inhibition. Here, we investigated the RyR2 inhibitory action of the CaM p.Phe142Leu mutation (F142L; numbered including the start-Met), which markedly reduces CaM Ca²⁺ binding. Surprisingly, CaM-F142L had little to no aberrant effect on RyR2-mediated store overload-induced Ca²⁺ release in HEK293 cells compared with CaM-WT. Furthermore, CaM-F142L enhanced CaM-dependent RyR2 inhibition at the single channel level compared with CaM-WT. This is in stark contrast to the actions of arrhythmogenic CaM mutations N54I, D96V, N98S, and D130G, which all diminish CaM-dependent RyR2 inhibition. Thermodynamic analysis showed that apoCaM-F142L converts an endothermal interaction between CaM and the CaM-binding domain (CaMBD) of RyR2 into an exothermal one. Moreover, NMR spectra revealed that the CaM-F142L-CaMBD interaction is structurally different from that of CaM-WT at low Ca²⁺ These data indicate a distinct interaction between CaM-F142L and the RyR2 CaMBD, which may explain the stronger CaM-dependent RyR2 inhibition by CaM-F142L, despite its reduced Ca²⁺ binding. Collectively, these results add to our understanding of CaM-dependent regulation of RyR2 as well as the mechanistic effects of arrhythmogenic CaM mutations. The unique properties of the CaM-F142L mutation may provide novel clues on how to suppress excessive RyR2 Ca²⁺ release by manipulating the CaM-RyR2 interaction.2017-01-01T00:00:00Z2017 Jan2024-10-17T16:25:45.68Z2019-03-27T02:35:05ZS-EPMC52704812792798510.1074/jbc.M116.766253