Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P21817 (RyR1)
 1,154 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ryanodine receptors (RyRs) are intracellular channels that regulate the release of Ca2+ from the endoplasmic reticulum of many cell types. The RyRs are physically associated with FK506-binding proteins (FKBPs); immunophilins, with cis-trans peptidyl-prolyl isomerase activity. FKBP12 copurifies with RyR1 (skeletal isoform) and modulates its gating. A different form of FKBP with a slightly higher molecular weight copurifies with RyR2 (cardiac isoform). Previous studies have demonstrated that FKBP stablizes gating of the skeletal Ca(2+)-release channel. In the present study, we measured the activity of cardiac RyRs incorporated into planar lipid bilayers to show that rapamycin, a drug that inhibits the prolyl isomerase activity of FKBP and dissociates FKBP from the RyR, increases the open probability and reduces the current amplitude of cardiac muscle Ca(2+)-release channels. These experiments show for the first time that submicromolar concentrations of rapamycin can alter channel function. Our results provide support for the hypotheses that FKBP functionally associates with the RyR and that the immunosuppressant drug, rapamycin, alters the function of both cardiac and skeletal muscle isoforms of the Ca(2+)-release channel. Our findings suggest that FKBP-dependent modulation of channel function may be generally applicable to all members of the intracellular Ca(2+)-release channel family and that FKBPs may play important regulatory roles in many cell processes, ranging from long-term depression in neurons to contractility in cardiomyocytes.
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PMID:Effects of rapamycin on ryanodine receptor/Ca(2+)-release channels from cardiac muscle. 863 49

A 12-kDa immunophilin (FKBP12) is an integral component of the skeletal muscle ryanodine receptor (RyR). The RyR is a hetero-oligomeric complex with structural formula (FKBP)4(Ryr1)4, where Ryr1 is the 565-kDa product of the Ryr1 gene. To aid in the detection of the immunophilin's location in the receptor, we exchanged the FKBP12 present in RyR-enriched vesicles derived from sarcoplasmic reticulum with an engineered construct of FKBP12 fused to glutathione S-transferase and then isolated the complexes. Cryoelectron microscopy and image averaging of the complexes (in an orientation displaying the RyR's fourfold symmetry) revealed four symmetrically distributed, diffuse density regions that were located just outside the boundary defining the cytoplasmic assembly of the RyR. These regions are attributed to the glutathione transferase portion of the fusion protein because they are absent from receptors lacking the fusion protein. To more precisely define the location of FKBP12, we similarly analyzed complexes of RyR containing FKBP12 itself. Apparently some FKBP is lost during the purification or storage of the RyR because, to detect the receptor-bound immunophilin, it was necessary to add FKBP12 to the purified receptor before electron microscopy. Averaged images of these complexes showed a region of density that had not been observed previously in images of isolated receptors, and its position, along the edges of the transmembrane assembly, agreed with the position of the FKBP12 deduced from the experiments with the fusion protein. The proposed locations for FKBP12 are about 10 nm from the transmembrane baseplate assembly that contains the ion channel of the RyR.
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PMID:Cryoelectron microscopy resolves FK506-binding protein sites on the skeletal muscle ryanodine receptor. 878 29

The FK506 binding protein (FKBP12) is the cytosolic receptor for the immunosuppressant drugs FK506 and rapamycin. Recently, we have shown that FKBP12 copurifies with the ryanodine receptor (RyR), a 565,000-Da protein with four subunits that form the intracellular calcium release channels of the sarcoplasmic reticulum and endoplasmic reticulum. To identify the cellular function of FKBP12, in the absence of the ligands rapamycin and FK506, we coexpressed RyR and FKBP12 in insect cells. By measuring the single-channel properties of the RyR-FKBP complex reconstituted into planar lipid bilayers, we showed that FKBP12 modulates channel gating by decreasing channels with subconductance states, decreasing open probability after caffeine activation, and increasing mean open time. These effects were reversed by adding FK506 or rapamycin, both of which inhibit FKBP12 isomerase activity and dissociate the FKBP-RyR complex. These studies provided a natural cellular (ligand-independent) function for FKBP12 and established that the functional calcium release channel complex includes FKBP12. We also expressed recombinant RyR1 in Xenopus laevis oocytes that lack FKBP12. Functional studies showed that the properties of the cloned RyR1, expressed in oocytes, were comparable to those of the native RyR1. These studies showed that FKBP12 is not required for tetrameric formation of the channel structure or for insertion into an intracellular calcium-containing membrane. Both insect cells (Sf9) and Xenopus oocytes are excellent models for heterologous expression of FKBP12 and RyR. Combined with determination of the single-channel properties of the resulting complex reconstituted into planar lipid bilayers, these approaches are well suited to the study of the role of FKBP12 as a modulator of calcium channel function.
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PMID:Immunophilin Modulation of Calcium Channel Gating 881 65

In this report we demonstrate that the immunosuppressive drug, rapamycin, can reversibly activate the skeletal muscle ryanodine receptor calcium release channel (RyR) in terminal cisternae vesicles incorporated into planar lipid bilayers. This reveals a second mechanism of activation of RyRs by rapamycin. Irreversible channel activation and openings to subconductance levels are seen when rapamycin forms a complex with and removes the tightly bound 12 kDa FK506-binding protein (FKBP12) from the RyR. We show here that micromolar rapamycin activates RyRs which were previously 'stripped' of > 95% of their FKBP12s. Rapamycin caused a 6-fold increase in mean current, which was largely reversible, but no increase in the fraction of openings to subconductance levels. Therefore native RyRs, stripped of FKBP12, are directly activated by the macrocyclic lactone, rapamycin.
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PMID:Ryanodine receptors from rabbit skeletal muscle are reversibly activated by rapamycin. 914 79

In the present study, we compare functional consequences of dissociation and reconstitution of binding proteins FKBP12 and FKBP12.6 with ryanodine receptors from cardiac (RyR2) and skeletal muscle (RyR1). The skeletal muscle RyR1 channel became activated on removal of endogenously bound FKBP12, consistent with previous reports. Both FKBP12 and FKBP12.6 rebind to FKBP-depleted RyR1 and restore its quiescent channel behavior by altering ligand sensitivity, as studied by single-channel recordings in planar lipid bilayers, and macroscopic behavior of the channels (ryanodine binding and net energized Ca2- uptake). By contrast, removal of FKBP12.6 from the cardiac RyR2 did not modulate the function of the channel using the same types of assays as for RyR1. FKBP12 or FKBP12.6 had no effect on channel activity of FKBP12.6-depleted cardiac RyR2, although FKBP12.6 rebinds. Our studies reveal important differences between the two ryanodine receptor isoforms with respect to their functional interaction with FKBP12 and FKBP12.6.
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PMID:Different interactions of cardiac and skeletal muscle ryanodine receptors with FK-506 binding protein isoforms. 917 65

FKBP12, a cis-trans prolyl isomerase that binds the immunosuppressants FK506 and rapamycin, is ubiquitously expressed and interacts with proteins in several intracellular signal transduction systems. Although FKBP12 interacts with the cytoplasmic domains of type I receptors of the transforming growth factor-beta (TGF-beta) superfamily in vitro, the function of FKBP12 in TGF-beta superfamily signalling is controversial. FKBP12 also physically interacts stoichiometrically with multiple intracellular calcium release channels including the tetrameric skeletal muscle ryanodine receptor (RyR1). In contrast, the cardiac ryanodine receptor, RyR2, appears to bind selectively the FKBP12 homologue, FKBP12.6. To define the functions of FKBP12 in vivo, we generated mutant mice deficient in FKBP12 using embryonic stem (ES) cell technology. FKBP12-deficient mice have normal skeletal muscle but have severe dilated cardiomyopathy and ventricular septal defects that mimic a human congenital heart disorder, noncompaction of left ventricular myocardium. About 9% of the mutants exhibit exencephaly secondary to a defect in neural tube closure. Physiological studies demonstrate that FKBP12 is dispensable for TGF-beta-mediated signalling, but modulates the calcium release activity of both skeletal and cardiac ryanodine receptors.
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PMID:Cardiac defects and altered ryanodine receptor function in mice lacking FKBP12. 946 Dec 16

Excitation-contraction coupling in skeletal muscle requires the release of intracellular calcium ions (Ca2+) through ryanodine receptor (RyR1) channels in the sarcoplasmic reticulum. Half of the RyR1 channels are activated by voltage-dependent Ca2+ channels in the plasma membrane. In planar lipid bilayers, RyR1 channels exhibited simultaneous openings and closings, termed "coupled gating." Addition of the channel accessory protein FKBP12 induced coupled gating, and removal of FKBP12 uncoupled channels. Coupled gating provides a mechanism by which RyR1 channels that are not associated with voltage-dependent Ca2+ channels can be regulated.
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PMID:Coupled gating between individual skeletal muscle Ca2+ release channels (ryanodine receptors) 971 84

The ryanodine receptor/calcium release channel (RyR1) of sarcoplasmic reticulum from rabbit skeletal muscle terminal cisternae (TC) contains four tightly associated FK506-binding proteins (FKBP12). Dissociation and reconstitution studies have shown that RyR1 can be modulated by FKBP12, which helps to maintain the channel in the quiescent state. In this study, we found that the association of FKBP with RyR1 of skeletal muscle is common to each of the five classes of vertebrates. TC from skeletal muscle representing animals from different vertebrates, i.e. mammals (rabbit), birds (chicken), reptiles (turtle), fish (salmon and rainbow trout), and amphibians (frog), were isolated. For each, we find the following: 1) FKBP12 is localized to the TC (there are four FKBP binding sites/ryanodine receptor); 2) soluble FKBP exchanges with the bound form on RyR1 of TC; 3) release of FKBP from terminal cisternae by drug (FK590) treatment leads to a significant reduction in the net calcium loading rate, consistent with channel activation (the calcium loading rate is restored to the control value by reconstitution with FKBP12); and 4) RyR1 of skeletal muscle TC can bind to and exchange with either FKBP12 or FKBP12.6 (FKBP12.6 is the novel FKBP isoform found selectively associated with RyR2 of dog cardiac sarcoplasmic reticulum). We conclude that FKBP is an integral part of the RyR1 of skeletal muscle in each of the classes of vertebrate animals. The studies are consistent with a role for FKBP in skeletal muscle excitation-contraction coupling.
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PMID:FK-binding protein is associated with the ryanodine receptor of skeletal muscle in vertebrate animals. 985 7

FK506-binding protein (FKBP12) has been found to be associated with the skeletal muscle ryanodine receptor (RyR1) (calcium release channel), whereas FKBP12.6, a novel isoform of FKBP, is selectively associated with the cardiac ryanodine receptor (RyR2). For both RyRs, the stoichiometry is 4 FKBP/RyR. Although FKBP12.6 differs from FKBP12 by only 18 of 108 amino acids, FKBP12.6 selectively binds to RyR2 and exchanges with bound FKBP12.6 of RyR2, whereas both FKBP isoforms bind to RyR1 and exchange with bound FKBP12 of RyR1. To assess the amino acid residues of FKBP12.6 that are critical for selective binding to RyR2, the residues of FKBP12.6 that differ with FKBP12 were mutated to the respective residues of FKBP12. RyR2 of cardiac sarcoplasmic reticulum, prelabeled by exchange with [35S]FKBP12.6, was used as assay system for binding/exchange with the mutants. The triple mutant (Q31E/N32D/F59W) of FKBP12.6 was found to lack selective binding to the cardiac RyR2, comparable with that of FKBP12.0. In complementary studies, mutations of FKBP12 to the three critical amino acids of FKBP12.6, conferred selective binding to RyR2. Each of the FKBP12.6 and FKBP12 mutants retained binding to the skeletal muscle RyR1. We conclude that three amino acid residues (Gln31, Asn32, and Phe59) of human FKBP12.6 account for the selective binding to cardiac RyR2.
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PMID:Three amino acid residues determine selective binding of FK506-binding protein 12.6 to the cardiac ryanodine receptor. 1033 16

The present study documents the binding interaction of skeletal muscle sarcoplasmic reticulum (SR) transmembrane protein triadin with peripheral histidine-rich, Ca(2+)-binding protein (HCP). In addition to providing further evidence that HCP coenriches with RyR1, FKBP-12, triadin and calsequestrin (CS) in sucrose-density-purified TC vesicles, using specific polyclonal antibody, we show it to be expressed as a single protein species, both in fast-twitch and slow-twitch fibers, and to identically localize to the I-band. Colocalization of HCP and triadin at junctional triads is supported by the overlapping staining pattern using monoclonal antibodies to triadin. We show a specific binding interaction between digoxigenin-HCP and triadin, using ligand blot techniques. The importance of this finding is strengthened by the similarities in binding affinity and in Ca2+ dependence, (0.1-1 mM Ca2+) of the interaction of digoxigenin-HCP with immobilized TC vesicles. Suggesting that triadin dually interacts with HCP and with CS, at distinct sites, we have found that triadin-CS interaction in overlays does not require the presence of Ca2+. Consistent with the binding of CS to triadin luminal domain (Guo and Campbell, 1995), we show that binding sites for digoxigenin-CS, although not binding sites for digoxigenin-HCP, can be recovered in the 92 kDa triadin fragment, after chymotryptic cleavage of the NH2-terminal end of the folded molecule in intact TC vesicles. These differential effects form the basis for the hypothesis that HCP anchors to the junctional membrane domain of the SR, through binding to triadin short cytoplasmic domain at the NH2 terminus. Although the function of this interaction, as such, is not well understood, it seems of potential biological interest within the more general context of the structural-functional role of triadin at the triadic junction in skeletal muscle.
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PMID:Interaction of triadin with histidine-rich Ca(2+)-binding protein at the triadic junction in skeletal muscle fibers. 1053 21


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