PMID: 32317284

Authors:

Holt C, Hamborg L, Lau K, Brohus M, Sorensen AB, Larsen KT, Sommer C, Van Petegem F, Overgaard MT, Wimmer R

Title:

The arrhythmogenic N53I variant subtly changes the structure and dynamics in the calmodulin N-domain, altering its interaction with the cardiac ryanodine receptor.

Journal:

J Biol Chem. 2020 Apr 21. pii: RA120.013430. doi: 10.1074/jbc.RA120.013430.

Abstract:

Mutations in the genes encoding the highly conserved Ca(2+)-sensing protein calmodulin (CaM) cause severe cardiac arrhythmias, including catecholaminergic polymorphic ventricular tachycardia (CPVT) or long QT syndrome, and sudden cardiac death. Most of the identified arrhythmogenic mutations reside in the C-terminal domain of CaM, and mostly affect Ca(2+)-coordinating residues. One exception is the CPVT-causing N53I substitution, which resides in the N-terminal domain (N-domain). It does not affect Ca(2+)-coordination and has only a minor impact on binding affinity toward Ca(2+) and on other biophysical properties. Nevertheless, the N53I substitution dramatically affects CaM's ability to reduce the open probability of the cardiac ryanodine receptor (RyR2), while having no effect on the regulation of the plasmalemmal voltage-gated Ca(2+) channel, Cav1.2. To gain more insights into the molecular disease mechanism of this mutant, we used NMR to investigate the structures and dynamics of both apo- and Ca(2+)-bound CaM-N53I in solution. We also solved the crystal structures of wild-type and N53I CaM in complex with the primary calmodulin binding domain (CaMBD2) from RyR2 at 1.84-2.13 A resolutions. We found that all structures of the arrhythmogenic CaM-N53I variant are highly similar to those of wild type CaM. However, we noted that the N53I substitution exposes an additional hydrophobic surface, and that the intramolecular dynamics of the protein are significantly altered such that they destabilize the CaM N-domain. We conclude that the N53I-induced changes alter the interaction of the CaM N-domain with RyR2 and thereby likely cause the arrhythmogenic phenotype of this mutation.