CPVT-associated calmodulin variants N53I and A102V dysregulate calcium signalling via different mechanisms.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited condition that can cause fatal cardiac arrhythmia. Human mutations in the Ca2+ sensor calmodulin (CaM) have been associated with CPVT susceptibility, suggesting that CaM dysfunction is a key driver of the disease. However, the detailed molecular mechanism remains unclear. Focusing on the interaction with the cardiac ryanodine receptor (RyR2), we determined the effect of CPVT-associated variants N53I and A102V on the structural characteristics of CaM and on Ca2+ fluxes in live cells. We provide novel data showing that binding of both Ca2+/CaM-N53I and Ca2+/CaM-A102V to RyR23583-3603 is decreased. Ca2+/CaM:RyR23583-3603 high-resolution crystal structures highlight subtle conformational changes for the N53I variant, with A102V being similar to wild-type. We show that co-expression of CaM-N53I or CaM-A102V with RyR2 in HEK293 cells significantly increased the duration of Ca2+ events, CaM-A102V exhibited a lower frequency of Ca2+ oscillations. In addition, we show that CaMKIIδ phosphorylation activity is increased for A102V, compared to CaM-WT. This paper provides novel insight into the molecular mechanisms of CPVT-associated CaM variants and will facilitate development of strategies for future therapies.