Human Calmodulin Mutations

Abstract

Fluxes of calcium (Ca2+) across cell membranes enable fast cellular responses. Calmodulin (CaM) senses local changes in Ca2+ concentration and relays the information to numerous interaction partners. The critical role of accurate Ca2+ signaling on cellular function is underscored by the fact that there are three independent CaM genes (CALM1-3) in the human genome. All three genes are functional and encode the exact same CaM protein. Moreover, CaM has a completely conserved amino acid sequence across all vertebrates. Given this degree of conservation, it was long thought that mutations in CaM were incompatible with life. It was therefore a big surprise when the first CaM mutations in humans were identified six years ago. Today, more than a dozen human CaM missense mutations have been described, all found in patients with severe cardiac arrhythmias. Biochemical studies have demonstrated differential effects on Ca2+ binding affinities for these CaM variants. Moreover, CaM regulation of central cardiac ion channels is impaired, including the voltage-gated Ca2+ channel, CaV1.2, and the sarcoplasmic reticulum Ca2+ release channel, ryanodine receptor isoform 2, RyR2. Currently, no non-cardiac phenotypes have been described for CaM variant carriers. However, sequencing of large human cohorts reveals a cumulative frequency of additional rare CaM mutations that raise the possibility of CaM variants not exclusively causing severe cardiac arrhythmias. Here, we provide an overview of the identified CaM variants and their known consequences for target regulation and cardiac disease phenotype. We discuss experimental data, patient genotypes and phenotypes as well as which questions remain open to understand this complexity.

Diminished inhibition and facilitated activation of RyR2‐mediated Ca2+ release is a common defect of arrhythmogenic calmodulin mutations

“…The effect of CaM mutations on RyR2 regulation in cardiac cells is difficult to separate from effects on e.g. Ca V 1.2, Na V 1.5 and many other CaM signalling pathways, but the results presented here show such studies are well warranted to delineate the moelcular disease mechanism [2,[55][56][57].…”

“…Experiments with RyR2-expressing HEK293 cells approximate diastole-and early systole-like Ca 2+ conditions in cardiomyocytes and have repeatedly proven a valid model for investigating perturbations of cardiomyocyte intracellular Ca 2+ release [24,46,48,49,53,54]. One reason is that cardiac Ca 2+ -cycling requires tightly controlled Ca 2+ homeostasis and even small perturbations to RyR2 Ca 2+ release can cause severe disease [2,[55][56][57]. Taken together, our results indicate that all the 14 CaM mutations investigated cause increased SOICR activation and/or excessive Ca 2+ release through RyR2, albeit to various extents depending on cytosolic Ca 2+ concentrations.…”

Role of cardiac ryanodine receptor calmodulin‐binding domains in mediating the action of arrhythmogenic calmodulin N‐domain mutation N54I

“…Calmodulin is a central regulator of intracellular Ca 2+ release and excitation–contraction coupling in cardiomyocytes and mutations in CaM cause severe arrhythmias . One erroneous regulation caused by the CaM mutations is a diminished CaM‐dependent inhibition of RyR2‐mediated Ca 2+ release from the ER/SR Ca 2+ store .…”

Using deep mutational scanning to benchmark variant effect predictors and identify disease mutations

“…Of the 11 human proteins with DMS datasets, 7 have known pathogenic or likely pathogenic missense variants in ClinVar (93 for BRCA1, 31 for HRAS, 189 for P53, 108 for PTEN, 9 for CALM1, 5 for TPK1 and 2 for MAPK1). For CALM1 and TPK1, we identified additional pathogenic missense mutations in the literature (40)(41)(42)(43)(44), leading to a total of 19 for CALM1 and 8 for TPK1. MAPK1 has too few recorded pathogenic variants to include in this analysis.…”