High impact information on JSRP1

• A new structure consisting of bridges spanning the junctional gap is described, and a model is proposed in which the cytoplasmic but not the luminal membrane leaflets of the transverse tubule and of the junctional sarcoplasmic reticulum (SR) are continuous [1].
• The HRC gene encodes the histidine-rich calcium-binding protein, which is found in the lumen of the junctional sarcoplasmic reticulum (SR) of cardiac and skeletal muscle and within calciosomes of arterial smooth muscle [2].
• The novel skeletal muscle sarcoplasmic reticulum JP-45 protein. Molecular cloning, tissue distribution, developmental expression, and interaction with alpha 1.1 subunit of the voltage-gated calcium channel [3].
• Double immunofluorescence of adult skeletal muscle fibers demonstrates that JP-45 co-localizes with the sarcoplasmic reticulum calcium release channel [3].
• Extended junctional sarcoplasmic reticulum of avian cardiac muscle contains functional ryanodine receptors [4].

Biological context of JSRP1

• The results may be explained by a modulatory effect of JP-45 related to its reported in vitro interaction with the dihydropyridine receptor and the SR Ca(2+) binding protein calsequestrin (CSQ) [5].
• Effect of changes in action potential spike configuration, junctional sarcoplasmic reticulum micro-architecture and altered t-tubule structure in human heart failure [6].
• We measured the kinetics of calcium dissociation from calsequestrin in solution or forming part of isolated junctional sarcoplasmic reticulum membranes by mixing calsequestrin equilibrated with calcium with calcium-free solutions in a stopped-flow system [7].
• A protein complex present at the junctional sarcoplasmic reticulum (SR) membrane is implicated in the Ca(2+) release process during muscle contraction [8].
• Rapid kinetic characterization of active transport and passive release of calcium in vesicular fragments of longitudinal and junctional sarcoplasmic reticulum [9].

Anatomical context of JSRP1

• JP-45 is a novel integral protein constituent of the skeletal muscle sarcoplasmic reticulum junctional face membrane [3].
• Fractionation of the triadic junction into junctional transverse tubular membranes and junctional sarcoplasmic reticulum membranes has shown that dystrophin is enriched in junctional transverse tubular membranes [10].
• The formation of these complexes of cisterns was regarded as an extreme form of overdevelopment of extended junctional sarcoplasmic reticulum in atrial muscle cells [11].
• Furthermore, the location of junctional sarcoplasmic reticulum and transverse tubule membranes is maintained in myotubes in which the I-Z-I have been removed and the regular disposition of the intermediate filaments is disrupted, supporting a role for sarcoplasmic reticulum in the proper positioning of triad junctions [12].
• Both these values exceed the limit of resolution of the optical system, but their similarity suggests that at high [EGTA] the Ca(2+) domains in adult mammalian muscle fibers are confined to Ca(2+) release sites located at the junctional sarcoplasmic reticulum (SR) [13].

Associations of JSRP1 with chemical compounds

• The glycoprotein calsequestrin (CS) is segregated to the junctional sarcoplasmic reticulum (jSR) and is responsible for intraluminal Ca(2+) binding [14].

Physical interactions of JSRP1

• Junctin is a calsequestrin binding protein detected in junctional sarcoplasmic reticulum of striated muscles [15].

Other interactions of JSRP1

• At higher resolution with immunogold electron microscopy, we observed that DMPK is localized at the cytoplasmic surface of junctional and extended junctional sarcoplasmic reticulum, suggesting that DMPK is involved in the regulation of excitation-contraction coupling [16].

Analytical, diagnostic and therapeutic context of JSRP1

• Co-immunoprecipitation experiments with a monoclonal antibody against JP-45 show that JP-45 interacts with the alpha1.1 subunit voltage-gated calcium channel and calsequestrin [3].
• Western blot analysis revealed that isolated triads contained the integral membrane subunits gp91(phox) and p22(phox), which were markedly enriched in isolated transverse tubules but absent from junctional sarcoplasmic reticulum vesicles [17].
• For this purpose, we expressed JP-45 C-terminally tagged with the fluorescent protein DsRed2 by nuclear microinjection in myotubes derived from the C2C12 skeletal muscle cell line and performed whole-cell voltage-clamp experiments [5].
• Immunoelectron microscopy showed that the kinase was mainly expressed in both corbular and junctional sarcoplasmic reticulum, but not in network sarcoplasmic reticulum [18].
• We have used electron-probe microanalysis (EPMA) to address the question of Ca2+ release by junctional sarcoplasmic reticulum (JSR) as well as Ca2+ regulation by mitochondria (MT) during cardiac muscle contraction [19].

References