Spyros Zissimopoulos

Swansea University | SWAN · Medical School

The ryanodine receptor (RyR) is a homotetrameric channel mediating sarcoplasmic reticulum Ca ²⁺ release required for skeletal and cardiac muscle contraction. Mutations in RyR1 and RyR2 lead to life-threatening malignant hyperthermia episodes and ventricular tachycardia, respectively. In this brief report, we use chemical cross-linking to demonstrat...

The ryanodine receptor (RyR2) has a critical role in controlling Ca2+ release from the sarcoplasmic reticulum (SR) throughout the cardiac cycle. RyR2 protein has multiple functional domains with specific roles, and four of these RyR2 protomers are required to form the quaternary structure that comprises the functional channel. Numerous mutations in...

Two-pore channels are ion channels expressed on acidic organelles such as the various vesicles that constitute the endo-lysosomal system. They are permeable to Ca2+ and Na+ and activated by the second messenger NAADP as well as the phosphoinositide, PI(3,5)P2 and/or voltage. Here, we review the proteins that interact with these channels including r...

Rationale: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare disease, manifested by syncope or sudden death in children or young adults under stress conditions. Mutations in the Ca ²⁺ release channel/ryanodine receptor (RyR2) gene account for about 60% of the identified mutations. Recently, we found and described a mutation in...

Aims The cardiac ryanodine receptor (RyR2), which mediates intracellular Ca2+ release to trigger cardiomyocyte contraction, participates in development of acquired and inherited arrhythmogenic cardiac disease. This study was undertaken to characterize the network of inter- and intra-subunit interactions regulating the activity of the RyR2 homotetr...

The cardiac muscle ryanodine receptor-Ca2+ release channel (RyR2) constitutes the sarcoplasmic reticulum (SR) Ca2+ efflux mechanism that initiates myocyte contraction, while cardiac myosin binding protein-C (cMyBP-C) mediates regulation of acto-myosin cross-bridge cycling. In this report, we provide the first evidence for the presence of direct int...

Cardiac muscle contraction requires sarcoplasmic reticulum (SR) Ca(2+) release mediated by the quaternary complex comprising the ryanodine receptor (RyR2), calsequestrin (CSQ2), junctin and triadin. Here, we demonstrate that a direct interaction exists between RyR2 and CSQ2. Topologically, CSQ2 binding occurs at the first luminal loop of RyR2. Co-e...

Oligomerization is often a structural requirement for proteins to accomplish their specific cellular function. For instance, tetramerization of the ryanodine receptor (RyR) is necessary for the formation of a functional Ca(2+) release channel pore. Here, we describe detailed protocols for the assessment of protein self-association, including yeast...

The ryanodine receptor/Ca2+ release channel plays a pivotal role in skeletal and cardiac muscle excitation-contraction coupling. Defective regulation leads to neuromuscular disorders and arrhythmogenic cardiac disease. This mini-review focuses on channel regulation through structural intra- and inter-subunit interactions and their implications in r...

Catecholaminergic polymorphic ventricular tachycardia is a malignant disease, due to mutations in proteins controlling Ca2+ homeostasis. While the phenotype is characterized by polymorphic ventricular arrhythmias under stress, supraventricular arrhythmias may occur and are not fully characterized.Methods Twenty-five relatives from a Spanish family...

Catecholaminergic polymorphic ventricular tachycardia is a malignant disease, due to mutations in proteins controlling Ca2+ homeostasis. While the phenotype is characterized by polymorphic ventricular arrhythmias under stress, supraventricular arrhythmias may occur and are not fully characterized.Methods Twenty-five relatives from a Spanish family...

The ryanodine receptor (RyR2) is an intracellular Ca(2+) release channel essential for cardiac excitation-contraction coupling. Abnormal RyR2 channel function results in the generation of arrhythmias and sudden cardiac death. The present study was undertaken to investigate the mechanistic basis of RyR2 dysfunction in inherited arrhythmogenic cardia...

Ryanodine receptors type 2 (RyR2) regulate excitation-contraction coupling. Their dysfunction leads to pathological states, such as arrhythmia, heart failure and sudden death. Our homology model detected comparable structural determinants in the pores of the K+ channel KcsA and RyR2. A Glycine hinge motif in the inner transmembrane helix of many K+...

Background: A hallmark of heart failure is impaired cytoplasmic Ca(2+) handling of cardiomyocytes. It remains unknown whether specific alterations in nuclear Ca(2+) handling via altered excitation-transcription coupling contribute to the development and progression of heart failure. Methods and results: Using tissue and isolated cardiomyocytes f...

Oligomerisation of all three mammalian ryanodine receptor isoforms, a structural requirement for normal intracellular Ca2+ release channel function, is displayed by the discrete N-terminal domain which assembles into homo- and hetero-tetramers. This is demonstrated in yeast, mammalian cells and native tissue by complementary yeast two-hybrid, chemi...

Two-pore channels (TPC1-3) are recently identified endolysosomal ion channels. The mechanism by which these channels are regulated at the molecular level is presently unclear. To identify putative protein regulators of TPCs, we performed unbiased transcriptome-wide screens using the yeast two-hybrid technique to identify potential protein-protein i...

The ryanodine receptor (RyR) is an ion channel composed of four identical subunits mediating calcium efflux from the endo/sarcoplasmic reticulum of excitable and non-excitable cells. We present several lines of evidence indicating that the RyR2 amino-terminus is capable of self-association. A combination of yeast two-hybrid screens, co-immunoprecip...

The inositol 1,4,5-trisphosphate receptor (IP3R) is a ubiquitously expressed intracellular calcium release channel composed of four ∼300kDa subunits. Calcium signalling mediated via the IP3R and the related ryanodine receptor (RyR) is involved in numerous cellular processes including fertilisation, gene transcription, neurotransmitter release and m...

The type 2 ryanodine receptor (RyR2) mediates calcium release from the sarcoplasmic reticulum of cardiomyocytes. RyR2 mutations found in three clusters including the amino-terminus are associated with arrhythmogenic cardiac disease. Arrhythmia-linked mutations are proposed to disrupt interactions between discrete functional domains within the RyR2...

The FK506-binding proteins (FKBP12 and FKBP12.6; also known as FKBP1A and FKBP1B, respectively) are accessory subunits of the ryanodine receptor (RyR) Ca(2+) release channel. Aberrant RyR2-FKBP12.6 interactions have been proposed to be the underlying cause of channel dysfunction in acquired and inherited cardiac disease. However, the stoichiometry...

The cardiac ryanodine receptor (RyR2) mediates the release of calcium from the sarcoplasmic reticulum of cardiac myocytes. The functional channel is composed of four identical subunits with the C-terminal part comprising the transmembrane domain predicted to form the Ca2+-conducting pore. The large N-terminal cytoplasmic portion of RyR2 is believed...

The mineralocorticoid pathway is involved in cardiac arrhythmias associated with heart failure through mechanisms that are incompletely understood. Defective regulation of the cardiac ryanodine receptor (RyR) is an important cause of the initiation of arrhythmias. Here, we examined whether the aldosterone pathway might modulate RyR function. Using...

In the present paper we show that distinct human RyR2 (ryanodine receptor type 2) inherited mutations expressed in mammalian cells exhibit either unaltered or increased FKBP12.6 (12.6 kDa FK506-binding protein) binding compared with the wild-type. Oxidizing conditions result in decreased FKBP12.6 binding, but to the same extent as for the wild-type...

The cardiac muscle ryanodine receptor-calcium release channel (RyR2) and its interaction with an accessory protein, FK506-binding protein (FKBP12.6), have been implicated in the molecular pathogenesis of acquired and inherited cardiac disease (e.g. catecholaminergic polymorphic ventricular tachycardia; CPVT). We have assessed the FKBP12.6 binding c...

BACKGROUND: The mineralocorticoid pathway is involved in cardiac arrhythmias associated with heart failure through mechanisms that are incompletely understood. Defective regulation of the cardiac ryanodine receptor (RyR) is an important cause of the initiation of arrhythmias. Here, we examined whether the aldosterone pathway might modulate RyR func...

The ryanodine receptor (RyR) is an intracellular calcium release channel located on the sarco(endo)plasmic reticulum of muscle and non-muscle cells. The functional channel is composed of four identical subunits of approximately 560 kDa, which combine to form a high-conductance cation-permeable protein pore. There are three mammalian RyR isoforms th...

The ryanodine receptor (RyR) calcium release channel functions as a redox sensor that is sensitive to channel modulators. The FK506-binding protein (FKBP) is an important regulator of channel activity, and disruption of the RyR2-FKBP12.6 association has been implicated in cardiac disease. In the present study, we investigated whether the RyR-FKBP a...

The RyR (ryanodine receptor)/calcium release channel contains a number of highly reactive thiol groups that endow it with redox sensitivity. In general, oxidizing conditions favour channel opening, while reducing conditions have the opposite effect. Thiol modification affects the channel sensitivity to its principal effectors, Ca2+, Mg2+ and ATP, a...

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited disease characterized by life threatening arrhythmias and mutations in the gene encoding the ryanodine receptor (RyR2). Disagreement exists on whether (1) RyR2 mutations induce abnormal calcium transients in the absence of adrenergic stimulation; (2) decreased affinity of...

Ca2+ stores were studied in a preparation of freshly dissociated terminals from hypothalamic magnocellular neurons. Depolarization from a holding level of -80 mV in the absence of extracellular Ca2+ elicited Ca2+ release from intraterminal stores, a ryanodine-sensitive process designated as voltage-induced Ca2+ release (VICaR). The release took one...

The ryanodine receptor (RyR) is a widely expressed intracellular calcium (Ca(2+))-release channel regulating processes such as muscle contraction and neurotransmission. Snapin, a ubiquitously expressed SNARE-associated protein, has been implicated in neurotransmission. Here, we report the identification of snapin as a novel RyR2-interacting protein...

The ryanodine receptor-calcium release channel complex (RyR) plays a pivotal role in excitation-contraction coupling in skeletal and cardiac muscle. RyR channel activity is modulated by interaction with FK506-binding protein (FKBP), and disruption of the RyR-FKBP association has been implicated in cardiomyopathy, cardiac hypertrophy, and heart fail...

The immunophilin, FK506-binding protein (FKBP12), is an essential component of the ryanodine receptor channel complex of skeletal muscle (RyR1) and modulates intracellular calcium signaling from the endoplasmic reticulum. The cardiac muscle RyR isoform (RyR2) specifically associates with a distinct FKBP isoform, FKBP12.6. Previous studies have led...

Specific interactions between adjacent ryanodine receptor (RyR) molecules to form ordered two-dimensional arrays in the membrane have been demonstrated using electron microscopy both in situ, in tissues and cells, and in vitro, with the purified protein. RyR interoligomeric association has also been inferred from observations of simultaneous channe...

The C-terminal 100 amino acids of the RyR (ryanodine receptor), referred to as the C-terminal tail, is a highly conserved sequence that is present in all known RyR isoforms and which has been implicated in channel function. Deleting the final 15 amino acids from the full-length skeletal muscle RyR resulted in an inactive channel, attributed to impa...