Comparison of the structure-function of five newly members of the calcin family.

Calcins are a group of scorpion toxin peptides specifically binding to ryanodine receptors (RyRs) with high affinity, and have the ability to activate and stabilize RyR in a long-lasting subconductance state. Five newly calcins synthesized compounds exhibit typical structural characteristics of a specific family through chemical synthesis and virtual analysis. As the calcins from the same species, Petersiicalcin1 and Petersiicalcin2, Jendekicalcin2 and Jendekicalcin3, have only one residue difference.

The Effect of Acidic Residues on the Binding between Opicalcin1 and Ryanodine Receptor from the Structure-Functional Analysis.

Calcin is a group ligand with high affinity and specificity for the ryanodine receptors (RyRs). Little is known about the effect of its acidic residues on the spacial structure as well as the interaction with RyRs. We screened the opicalcin1 acidic mutants and investigated the effect of mutation on activity.

OpiCa1-PEG-PLGA nanomicelles antagonize acute heart failure induced by the cocktail of epinephrine and caffeine.

Background: Reducing Ca content in the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs) by calcin is a potential intervention strategy for the SR Ca overload triggered by β-adrenergic stress in acute heart diseases.

Methods: OpiCal-PEG-PLGA nanomicelles were prepared by thin film dispersion, of which the antagonistic effects were observed using an acute heart failure model induced by epinephrine and caffeine in mice. In addition, cardiac targeting, self-stability as well as biotoxicity were determined.

Sorcin promotes migration in cancer and regulates the EGF-dependent EGFR signaling pathways.

The epidermal growth factor receptor (EGFR) is one of the main tumor drivers and is an important therapeutic target for many cancers. Calcium is important in EGFR signaling pathways. Sorcin is one of the most important calcium sensor proteins, overexpressed in many tumors, that promotes cell proliferation, migration, invasion, epithelial-to-mesenchymal transition, malignant progression and resistance to chemotherapeutic drugs.

Cryo-EM analysis of scorpion toxin binding to Ryanodine Receptors reveals subconductance that is abolished by PKA phosphorylation.

Calcins are peptides from scorpion venom with the unique ability to cross cell membranes, gaining access to intracellular targets. Ryanodine Receptors (RyR) are intracellular ion channels that control release of Ca from the endoplasmic and sarcoplasmic reticulum. Calcins target RyRs and induce long-lived subconductance states, whereby single-channel currents are decreased.

Preserved cardiac performance and adrenergic response in a rabbit model with decreased ryanodine receptor 2 expression.

Ryanodine receptor 2 (RyR2) is an ion channel in the heart responsible for releasing into the cytosol most of the Ca required for contraction. Proper regulation of RyR2 is critical, as highlighted by the association between channel dysfunction and cardiac arrhythmia. Lower RyR2 expression is also observed in some forms of heart disease; however, there is limited information on the impact of this change on excitation-contraction (e-c) coupling, Ca-dependent arrhythmias, and cardiac performance.

The V2475F CPVT1 mutation yields distinct RyR2 channel populations that differ in their responses to cytosolic Ca and Mg.

Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is a lethal genetic disease causing arrhythmias and sudden cardiac death in children and young adults and is linked to mutations in the cardiac ryanodine receptor (RyR2). The effects of CPVT1 mutations on RyR2 ion-channel function are often investigated using purified recombinant RyR2 channels homozygous for the mutation. However, CPVT1 patients are heterozygous for the disease, so this approach does not reveal the true changes to RyR2 function across the entire RyR2 population of channels in the heart.

Impaired Binding to Junctophilin-2 and Nanostructural Alteration in CPVT Mutation.

[Figure: see text].

Cardiac hypertrophy and arrhythmia in mice induced by a mutation in ryanodine receptor 2.

Hypertrophic cardiomyopathy (HCM) is triggered mainly by mutations in genes encoding sarcomeric proteins, but a significant proportion of patients lack a genetic diagnosis. We identified a novel mutation in the ryanodine receptor 2, RyR2-P1124L, in a patient from a genotype-negative HCM cohort. The aim of this study was to determine whether RyR2-P1124L triggers functional and structural alterations in isolated RyR2 channels and whole hearts.

Atrial Infarction-Induced Spontaneous Focal Discharges and Atrial Fibrillation in Sheep: Role of Dantrolene-Sensitive Aberrant Ryanodine Receptor Calcium Release.

Background: The mechanisms underlying spontaneous atrial fibrillation (AF) associated with atrial ischemia/infarction are incompletely elucidated. Here, we investigate the mechanisms underlying spontaneous AF in an ovine model of left atrial myocardial infarction (LAMI).

Methods And Results: LAMI was created by ligating the atrial branch of the left anterior descending coronary artery.

Structure-function relationships of peptides forming the calcin family of ryanodine receptor ligands.

Calcins are a novel family of scorpion peptides that bind with high affinity to ryanodine receptors (RyRs) and increase their activity by inducing subconductance states. Here, we provide a comprehensive analysis of the structure-function relationships of the eight calcins known to date, based on their primary sequence, three-dimensional modeling, and functional effects on skeletal RyRs (RyR1). Primary sequence alignment and evolutionary analysis show high similarity among all calcins (≥78.

Enhanced Classification of Brugada Syndrome-Associated and Long-QT Syndrome-Associated Genetic Variants in the SCN5A-Encoded Na(v)1.5 Cardiac Sodium Channel.

Background: A 2% to 5% background rate of rare SCN5A nonsynonymous single nucleotide variants (nsSNVs) among healthy individuals confounds clinical genetic testing. Therefore, the purpose of this study was to enhance interpretation of SCN5A nsSNVs for clinical genetic testing using estimated predictive values derived from protein-topology and 7 in silico tools.

Methods And Results: Seven in silico tools were used to assign pathogenic/benign status to nsSNVs from 2888 long-QT syndrome cases, 2111 Brugada syndrome cases, and 8975 controls.

Arrhythmogenesis in a catecholaminergic polymorphic ventricular tachycardia mutation that depresses ryanodine receptor function.

Current mechanisms of arrhythmogenesis in catecholaminergic polymorphic ventricular tachycardia (CPVT) require spontaneous Ca(2+) release via cardiac ryanodine receptor (RyR2) channels affected by gain-of-function mutations. Hence, hyperactive RyR2 channels eager to release Ca(2+) on their own appear as essential components of this arrhythmogenic scheme. This mechanism, therefore, appears inadequate to explain lethal arrhythmias in patients harboring RyR2 channels destabilized by loss-of-function mutations.

Arrhythmogenic mechanisms in ryanodine receptor channelopathies.

Ryanodine receptors (RyRs) are the calcium release channels of sarcoplasmic reticulum (SR) that provide the majority of calcium ions (Ca(2+)) necessary to induce contraction of cardiac and skeletal muscle cells. In their intracellular environment, RyR channels are regulated by a variety of cytosolic and luminal factors so that their output signal (Ca(2+)) induces finely-graded cell contraction without igniting cellular processes that may lead to aberrant electrical activity (ventricular arrhythmias) or cellular remodeling. The importance of RyR dysfunction has been recently highlighted with the demonstration that point mutations in RYR2, the gene encoding for the cardiac isoform of the RyR (RyR2), are associated with catecholaminergic polymorphic ventricular tachycardia (CPVT), an arrhythmogenic syndrome characterized by the development of adrenergically-mediated ventricular tachycardia in individuals with an apparently normal heart.

Caveolin-3 suppresses late sodium current by inhibiting nNOS-dependent S-nitrosylation of SCN5A.

Aims: Mutations in CAV3-encoding caveolin-3 (Cav3) have been implicated in type 9 long QT syndrome (LQT9) and sudden infant death syndrome (SIDS). When co-expressed with SCN5A-encoded cardiac sodium channels these mutations increased late sodium current (INa) but the mechanism was unclear. The present study was designed to address the mechanism by which the LQT9-causing mutant Cav3-F97C affects the function of caveolar SCN5A.

Digenic inheritance novel mutations in SCN5a and SNTA1 increase late I(Na) contributing to LQT syndrome.

SCN5A and SNTA1 are reported susceptible genes for long QT syndrome (LQTS). This study was designed to elucidate a plausible pathogenic arrhythmia mechanism for the combined novel mutations R800L-SCN5A and A261V-SNTA1 on cardiac sodium channels. A Caucasian family with syncope and marginally prolonged QT interval was screened for LQTS-susceptibility genes and found to harbor the R800L mutation in SCN5A and A261V mutation in SNTA1, and those with both mutations had the strongest clinical phenotype.

LQTS-associated mutation A257G in α1-syntrophin interacts with the intragenic variant P74L to modify its biophysical phenotype.

The -encoded α1-syntrophin (SNTA1) missense mutation, p.A257G, causes long QT syndrome (LQTS) by pathogenic accentuation of Nav1.5's sodium current ().

Fatty acids antagonize bupivacaine-induced I(Na) blockade.

Theories regarding the mechanism of intravenous fat emulsion for bupivacaine cardiotoxicity include creation of an intravascular lipid sink into which the cardiotoxic drug is sequestered, an improvement of impaired cardiac metabolism, and restoration of cardiomyocyte function by increasing intracellular calcium. However, work in this area is inconclusive and a more mechanistic explanation is desirable. We used a heterologous expression system (HEK-293 cells) and voltage clamp techniques to study the electrophysiologic effects of bupivacaine, polyunsaturated, and saturated fatty acids on sodium current (I(Na)) in stable cell lines expressing human cardiac sodium channels.

The common African American polymorphism SCN5A-S1103Y interacts with mutation SCN5A-R680H to increase late Na current.

The common polymorphism SCN5A-S1103Y (∼13% allelic frequency in African Americans) is a risk factor for arrhythmia, sudden unexplained death (SUD), and sudden infant death syndrome. Prompted by a case of autopsy-negative SUD in a 23-year-old African American man who collapsed while playing football, we hypothesized that S1103Y interacted with other SCN5A variants to pathologically modify sodium current (I(Na)). Mutational analysis of arrhythmia-associated genes in the victim revealed the variants SCN5A-R680H and SCN5A-S1103Y.

Sudden infant death syndrome-associated mutations in the sodium channel beta subunits.

Background: Approximately 10% of sudden infant death syndrome (SIDS) cases may stem from potentially lethal cardiac channelopathies, with approximately half of channelopathic SIDS involving the Na(V)1.5 cardiac sodium channel. Recently, Na(V) beta subunits have been implicated in various cardiac arrhythmias.