Phylogenetic and biochemical analysis of calsequestrin structure and association of its variants with cardiac disorders

Abstract

Calsequestrin is among the most abundant proteins in muscle sarcoplasmic reticulum and displays a high capacity but a low affinity for Ca2+ binding. In mammals, calsequestrin is encoded by two genes, CASQ1 and CASQ2, which are expressed almost exclusively in skeletal and cardiac muscles, respectively. Phylogenetic analysis indicates that calsequestrin is an ancient gene in metazoans, and that the duplication of the ancestral calsequestrin gene took place after the emergence of the lancelet. CASQ2 gene variants associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) in humans are positively correlated with a high degree of evolutionary conservation across all calsequestrin homologues. The mutations are distributed in diverse locations of the calsequestrin protein and impart functional diversity but remarkably manifest in a similar phenotype in humans.

The Structural–Functional Crosstalk of the Calsequestrin System: Insights and Pathological Implications

“…Skeletal CASQ1 pathological missense mutations in heterozygous conditions are linked to either malignant hyperthermia (CASQ1 M87T) or tubular aggregate myopathy (CASQ1 D44N, G103D, D244G, I387T) [15,83,84], whereas the numerous pathological mutations of the cardiac isoform lead to Catecholaminergic Polymorphic Ventricular Tachycardia type 2 (CPVT2) mainly in homozygosis [31,36,85]. CASQ1 and CASQ2 missense mutations are scattered across all three thioredoxin domains of CASQ and the mutated proteins do not share any common defect in their Ca 2+ -dependent polymerization properties [31,36,85,86].…”

“…Skeletal CASQ1 pathological missense mutations in heterozygous conditions are linked to either malignant hyperthermia (CASQ1 M87T) or tubular aggregate myopathy (CASQ1 D44N, G103D, D244G, I387T) [15,83,84], whereas the numerous pathological mutations of the cardiac isoform lead to Catecholaminergic Polymorphic Ventricular Tachycardia type 2 (CPVT2) mainly in homozygosis [31,36,85]. CASQ1 and CASQ2 missense mutations are scattered across all three thioredoxin domains of CASQ and the mutated proteins do not share any common defect in their Ca 2+ -dependent polymerization properties [31,36,85,86]. Moreover, most of the published biochemical analyses on either the polymerization and/or Ca 2+ -buffering capabilities of recombinant CASQ missense pathological mutants [15,28,31,[33][34][35][36][85][86][87][88][89][90] (Table 1) are sometimes difficult to interpret or in contrast with each other.…”

“…CASQ1 and CASQ2 missense mutations are scattered across all three thioredoxin domains of CASQ and the mutated proteins do not share any common defect in their Ca 2+ -dependent polymerization properties [31,36,85,86]. Moreover, most of the published biochemical analyses on either the polymerization and/or Ca 2+ -buffering capabilities of recombinant CASQ missense pathological mutants [15,28,31,[33][34][35][36][85][86][87][88][89][90] (Table 1) are sometimes difficult to interpret or in contrast with each other. Table 1.…”

“…A first limitation that may have led to this situation is the previously described hyper sensitivity of CASQ to the ionic conditions [85,86]. Secondly, the very intimate relationship between Ca 2+ -binding events and polymerization complicates the interpretation of Ca 2+ -binding curves, particularly those obtained with methods such as MicroScale Thermophoresis, which are sensitive to changes in molecular size.…”

How Functional Genomics Can Keep Pace With VUS Identification

“…Combined, ClinVar reports >3400 VUS or with conflicting interpretations for these calcium handling proteins ( Figure 2A ). While HTP functional analysis is lacking for CASQ2 and Cav1.2, numerous functional assays have been described for CASQ2 ( 83 ) and automated patch clamp has been reported for pharmacological screening of Cav1.2 using HEK 293 cells. While this latter system should be adaptable for HTP functional analysis, Cav1.2 is more complex requiring its two subunits and an inward rectifier for optimization ( 84 ).…”