The catecholaminergic polymorphic ventricular tachycardia mutation R33Q disrupts the N-terminal structural motif that regulates reversible calsequestrin polymerization.
Calsequestrin undergoes dynamic polymerization with increasing calcium concentration by front-to-front dimerization and back-to-back packing, forming wire-shaped structures. A recent finding that point mutation R33Q leads to lethal catecholaminergic polymorphic ventricular tachycardia (CPVT) implies a crucial role for the N terminus. In this study, we demonstrate that this mutation resides in a highly conserved alternately charged residue cluster (DGKDR; cluster 1) in the N-terminal end of calsequestrin. We further show that this cluster configures itself as a ring system and that the dipolar arrangement within the cluster brings about a critical conformational flip of Lys(31)-Asp(32) essential for dimer stabilization by formation of a H-bond network. We additionally show that Ca(2+)-induced calsequestrin aggregation is nonlinear and reversible and can regain the native conformation by Ca(2+) chelation with EGTA. This study suggests that cluster 1 works as a molecular switch and governs the bidirectional transition between the CASQ2 monomer and dimer. We further demonstrate that mutations disrupting the alternating charge pattern of the cluster, including R33Q, impair Ca(2+)-CASQ2 interaction, leading to altered polymerization-depolymerization dynamics. This study provides new mechanistic insight into the functional effects of the R33Q mutation and its potential role in CPVT.
Bal
Naresh C
NC
Department of Physiology and Cell Biology, The Ohio State University College of Medicine, and the Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA.
Sharon
Ashoke
A
Gupta
Subash C
SC
Jena
Nivedita
N
Shaikh
Sana
S
Gyorke
Sandor
S
Periasamy
Muthu
M
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002155:Calsequestrin / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D002938:Ciona intestinalis; D019295:Computational Biology / Q000379:methods; D019281:Dimerization; D004533:Egtazic Acid / Q000737:chemistry; D006801:Humans; D006860:Hydrogen Bonding; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D051381:Rats; D017386:Sequence Homology, Amino Acid; D017180:Tachycardia, Ventricular / Q000235:genetics* / Q000378:metabolism
D002155:Calsequestrin; D002395:Catecholamines; D002614:Chelating Agents; D004533:Egtazic Acid; D002118:Calcium