CPVT-associated calmodulin variants N53I and A102V dysregulate Ca(2+) signalling via different mechanisms

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited condition that can cause fatal cardiac arrhythmia. Human mutations in the Ca(2+) 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 Ca(2+) fluxes in live cells. We provide novel data showing that interaction of both Ca(2+)/CaM-N53I and Ca(2+)/CaM-A102V with the RyR2 binding domain is decreased. Ca(2+)/CaM–RyR2(3583-3603) high-resolution crystal structures highlight subtle conformational changes for the N53I variant, with A102V being similar to wild type (WT). We show that co-expression of CaM-N53I or CaM-A102V with RyR2 in HEK293 cells significantly increased the duration of Ca(2+) events; CaM-A102V exhibited a lower frequency of Ca(2+) oscillations. In addition, we show that CaMKIIδ (also known as CAMK2D) 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 the development of strategies for future therapies.