Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Calsequestrin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources

Photolabeling of the integral proteins of skeletal muscle sarcoplasmic reticulum: comparison of junctional and nonjunctional membrane fractions.

Rabbit skeletal muscle sarcoplasmic reticulum (SR) was fractionated by isopycnic density gradient centrifugation into longitudinal tubules (LSR) and terminal cisternae (TC). Junctional face membranes (JFM) were obtained by Triton X-100 treatment of the TC fraction (Costello, B., Chadwick, C., Saito, A., Chu, A., Maurer, A. and Fleischer, S. (1986) J. Cell Biol. 103, 741-753). Photoactivatable phospholipid analogs were introduced into LSR, TC, and JFM fractions to specifically label integral membrane proteins. Remarkably different labeling patterns were observed. Proteins of the following Mr were labeled and identified in the junctional sarcoplasmic reticulum (JFM): 350,000, 325,000, 80,000, 49,000, 37,000, 32,000, 30,000, and 6000. Polypeptides of Mr 105,000 (Ca2+-dependent ATPase), 77,000, 55,000, 41,000, 22,000, and 9000 (proteolipid) were labeled and found to be selectively localized in the nonjunctional sarcoplasmic reticulum (LSR). Calsequestrin, a key protein responsible for Ca2+ storage within the SR lumen, was never labeled, whether 1 mM CaCl2 was present or absent, and is termed a nonintegral membrane protein.

Affinity Labels↗

Polylysine induces a rapid Ca2+ release from sarcoplasmic reticulum vesicles by mediation of its binding to the foot protein.

The addition of polylysine to a heavy fraction of sarcoplasmic reticulum (SR) vesicles produces a rapid Ca2+ release with no appreciable lag period. The polylysine concentration for half-maximal activation (C1/2) is approximately 0.99 micrograms/ml, or 0.3 microM, the lowest C 1/2 for Ca2+ release-inducing reagents reported in the literature. The time course and the [Ca2+] dependence of polylysine-induced release are similar to those of caffeine-induced Ca2+ release. At higher concentrations of polylysine (e.g., 10 micrograms/ml), however, little or no Ca2+ release occurs. Upon photolysis of SR vesicles with the photocrosslinkable radiolabeled polylysine derivative, [3H]succinimidyl azido benzoate polylysine, 0.28 and 0.52-1.2 mol polylysine were bound to 1 mol of the 400-kDa foot protein at activating (3 micrograms/ml) and inhibitory (10 micrograms/ml) concentrations of polylysine, respectively. On the other hand, the amounts of polylysine bound to the other SR proteins (mol/mol) were negligible (e.g., less than or equal to 0.0127 mol polylysine/mol calsequestrin). This suggests that the binding of polylysine to the foot protein is responsible not only for the induction of release but also for inactivation. These results provide direct evidence that the receptor for the chemical trigger of Ca2+ release is localized within the foot protein. Ruthenium red, which inhibits polylysine-induced Ca2+ release, does not inhibit polylysine binding to the foot protein, suggesting that the polylysine binding domain of the foot protein is different from the channel domain.

Affinity Labels↗

Modification of acidic residues normalizes sodium dodecyl sulfate-polyacrylamide gel electrophoresis of caldesmon and other proteins that migrate anomalously.

Caldesmon migrates as a 140-kDa protein during polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), although its true molecular mass is close to 90 kDa. Since caldesmon's high acidic residue content may be responsible for this anomaly, it was reasoned that modification of these residues, with a loss of negative charge, might restore normal electrophoretic migration. Therefore caldesmon was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide in the presence of excess ethanolamine, which results in negatively charged carboxylates being converted to neutral amides without protein cross-linking. The absence of cross-linking was shown by rotary shadow electron microscopy. In accord with expectations, modified caldesmon migrated as a 94-kDa protein when compared to standards, which were much less affected by modification. The anomalous migration of caldesmon might be due to the repulsion of negatively charged SDS by caldesmon's acidic residues. Low binding of SDS to caldesmon is consistent with the fact that SDS, up to 1%, had little or no effect on the secondary structure of caldesmon, as monitored by circular dichroism. However, other mechanisms can also explain these observations. The abnormal migration of tropomyosin and calsequestrin, both of which have a high percentage of acidic amino acids, was also "normalized" by this treatment. Thus this method might have general application for the electrophoresis of proteins which have a high acidic residue content and migrate anomalously.

Calmodulin-Binding Proteins↗

Enhanced Ca2+-induced calcium release by isolated sarcoplasmic reticulum vesicles from malignant hyperthermia susceptible pig muscle.

To further define the possible involvement of sarcoplasmic reticulum calcium accumulation and release in the skeletal muscle disorder malignant hyperthermia (MH), we have examined various properties of sarcoplasmic reticulum fractions isolated from normal and MH-susceptible pig muscle. A sarcoplasmic reticulum preparation enriched in vesicles derived from the terminal cisternae, was further fractionated on discontinuous sucrose density gradients (Meissner, G. (1984) J. Biol. Chem. 259, 2365-2374). The resultant MH-susceptible and normal sarcoplasmic reticulum fractions, designated F0-F4, did not differ in yield, cholesterol and phospholipid content, or nitrendipine binding capacity. Calcium accumulation (0.27 mumol Ca/mg per min at 22 degrees C), Ca2+-ATPase activity (0.98 mumol Pi/mg per min at 22 degrees C), and calsequestrin content were also similar for MH-susceptible and normal sarcoplasmic reticulum fraction F3. To examine sarcoplasmic reticulum calcium release, fraction F3 vesicles were passively loaded with 45Ca (approx. 40 nmol Ca/mg), and rapidly diluted into a medium of defined Ca2+ concentration. Upon dilution into 1 microM Ca2+, the extent of Ca2+-dependent calcium release measured after 5 s was significantly greater for MH-susceptible than for normal sarcoplasmic reticulum, 65.9 +/- 2.8% vs. 47.7 +/- 3.9% of the loaded calcium, respectively. The C1/2 for Ca2+ stimulation of this calcium release (5 s value) from MH-susceptible sarcoplasmic reticulum also appeared to be shifted towards a higher Ca2+-sensitivity when compared to normal sarcoplasmic reticulum. Dantrolene had no effect on calcium release from fraction F3, however, halothane (0.1-0.5 mM) increased the extent of calcium release (5 s) similarly in both MH-susceptible and normal sarcoplasmic reticulum. Furthermore, Mg2+ was less effective at inhibiting, while ATP and caffeine were more effective in stimulating, this Ca2+-dependent release of calcium from MH-susceptible, when compared to normal sarcoplasmic reticulum. Our results demonstrate that while sarcoplasmic reticulum calcium-accumulation appears unaffected in MH, aspect(s) of the sarcoplasmic reticulum Ca2+-induced calcium release mechanism are altered. Although the role of the Ca2+-induced calcium release mechanism of sarcoplasmic reticulum in situ is not yet clear, our results suggest that an abnormality in the regulation of sarcoplasmic reticulum calcium release may play an important role in the MH syndrome.

Animals↗

Covalent labeling of the cytoplasmic or luminal domains of the sarcoplasmic reticulum Ca(2+)-ATPase with fluorescent azido dyes.

Sarcoplasmic reticulum (SR) vesicles were incubated with azido derivatives of Cascade blue (ACB), Lucifer yellow (ALY), 2,7-naphthalene-disulfonic acid (ANDS), and fluorescein (AF) for 0.1-24 h at 2 degrees C. All four dyes gave intense reaction with the cytoplasmic domain of the Ca(2+)-ATPase on photoactivation after brief incubation. The penetration of the dyes into the luminal space of the SR was determined after centrifugation through Sephadex microcolumns to remove the external dye, followed by photolabeling and gel electrophoresis of the photolabeled proteins. The reaction of ACB and ANDS with the Ca(2+)-ATPase and with calsequestrin increased progressively during incubation up to 24 h indicating their slow accumulation in the luminal space, while ALY and AF did not show significant penetration into the vesicles. The distribution of the covalently attached ACB in the Ca(2+)-ATPase was tested by tryptic proteolysis after labeling exclusively from the outside (OS), from the inside (IS) or from both sides (BS). In all cases intense ACB fluorescence was seen in the A fragment with inhibition of ATPase activity. In the OS preparations the A1, while in IS the A2 fragment was more intensely labeled. There was no significant incorporation of ACB into the region of B fragment identified by FITC fluorescence. The crystallization of the Ca(2+)-ATPase by EGTA + decavanadate was completely inhibited in the BS samples after labeling either in the Ca2E1 or E2V conformation. There was no inhibition of crystallization in the OS preparations. In the IS preparations labeled in the Ca2E1 state the crystallization was impaired, while in the E2V state there was only slight disorganization of the crystals. The total amount of ACB photoincorporated into SR proteins after incubation for 24 h was 1.75 nmol/mg protein; 2/3 of this labeling occurred from the outside and 1/3 from the inside. Similar level of labeling was obtained in media that stabilize the E1 or the E2 conformation of the Ca(2+)-ATPase.

Amino Acid Sequence↗

Low-affinity Ca(2+)-binding sites versus Zn(2+)-binding sites in histidine-rich Ca(2+)-binding protein of skeletal muscle sarcoplasmic reticulum.

Histidine-rich Ca(2+)-binding protein (HRC) is a 170 kDa protein that can be identified in the isolated sarcoplasmic reticulum from rabbit skeletal muscle by its ability to bind [125I]low-density lipoprotein on blots after SDS-PAGE and that appears to be bound to the junctional membrane through calcium bridges. Molecular cDNA cloning of this protein predicts the existence of a Ca(2+)-binding domain and of a distinct heavy-metal binding domain at the cystein-rich COOH-terminus. Here we demonstrate, using radioactive ligand blot techniques, that HRC protein binds 45Ca at low affinity, as well as being able to bind 65Zn, but at different sites, that are largely inhibitable by prior reductive alkylation of the protein. In contrast to Ca(2+)-binding protein calsequestrin not having detectable 65Zn-binding sites, HRC protein bound selectively to immobilized Zn2+ on IDA-agarose affinity columns. Our results also indicate that rabbit and human 140 kDa HRC protein have common properties.

Animals↗

The calcium signal and neutrophil activation.

The cytosolic free calcium concentration, [Ca2+]i in phagocytic cells (e.g. neutrophils, human leukemic cell line HL-60) is an important determinant of cellular activity. In resting phagocytes [Ca2+]i is low (approximately 100 nM), but in response to occupation of cell surface receptors, it rises to micromolar levels, thereby activating a variety of cellular functions. The increases in [Ca2+]i consist of two components: an immediate that is independent of extracellular Ca2+, and a more delayed that is abolished by the removal of extracellular Ca2+. These two components reflect the involvement of two subcellular structures in intracellular Ca2+ homeostasis: an intracellular Ca2+ store, referred to as the calciosome; and the plasma membrane. The function of the intracellular Ca2(+)-store depends on a Ca2(+)-pump, functionally and immunologically related to the cardiac sarcoplasmic reticulum Ca2(+)-ATPase, a Ca2(+)-storage protein, similar to muscle calsequestrin, and a Ca2(+)-release channel, which is sensitive to inositol 1,4,5-trisphosphate. The Ca2(+)-regulatory function of the plasma membrane depends on a Ca2+ pump, similar to the erythrocyte-type Ca2(+)-ATPase, and a Ca2+ channel; the activity of the Ca2+ channel is closely coupled to phosphatidylinositol turnover.

Calcium↗

Characterization of sea urchin egg endoplasmic reticulum in cortical preparations.

The cortical endoplasmic reticulum (ER) of sea urchin eggs was localized on isolated egg cortices by staining with aqueous suspensions of the dicarbocyanine "DiI." Immunofluorescence localization of a calsequestrin-like protein was essentially identical; this is consistent with a role for the ER in calcium regulation. The ER often encircles cortical granules, making it well-suited for initiating fusion and propagating the calcium wave. Thiazole orange and Hoechst dye 33258 at pH 2 stain ribosomes bound to the ER, providing evidence that the cortical ER is rough ER. High chloride concentrations were found to disrupt ER continuity.

Animals↗

Characterization of the terminal cisternae and longitudinal tubules of sarcoplasmic reticulum from malignant hyperpyrexia susceptible porcine skeletal muscle.

1. The sarcoplasmic reticulum (SR) from malignant hyperpyrexia susceptible (MHS) and control porcine skeletal muscle was separated into vesicular fractions enriched in the membrane elements of the terminal cisternae and longitudinal tubules. 2. The two membrane preparations were highly purified and had distinctive features which were associated with their origins in the SR membraneous network. 3. Calsequestrin and calcium were enriched in the terminal cisternae fraction (HSR), in comparison to longitudinal tubule preparations (LSR). 4. The HSR membrane also had a greater total capacity to store Ca2+ and Ca2+ release was more rapid than from LSR preparations. 5. No distinction could be made between the membrane morphology, Ca2+ -fluxes or Ca2+ -dependent ATPase activities, associated with these functionally distinct regions of MHS and control preparations.

Animals↗

Analysis of sarcoplasmic reticulum proteins in patients susceptible to malignant hyperthermia.

It has been suspected that the cause of malignant hyperthermia (MH) is an abnormality in the sarcoplasmic reticulum of skeletal muscle. We isolated the sarcoplasmic reticulum from malignant hyperthermia-susceptible (MHS) patients and controls and analysed the protein composition with sodium dodecyl sulfate polyacrylamide gel electrophoresis. There were no remarkable changes in the sarcoplasmic reticulum protein composition profile of the scanned gel of the patients. Quantitative measurement of the relative proportion of each band in the gel, however, revealed a slight decrease in calsequestrin and a slight increase in protein of molecular weight 23,000. (Ca2+ -Mg2+)ATPase had no altered subfragments in MHS patients. Crude mitochondrial proteins and myoplasmic proteins showed minor alterations in composition in some patients. The data supported the thesis that malignant hyperthermia is due to defects in several different cell membranes including the sarcoplasmic reticulum and the mitochondria.

Disease Susceptibility↗

A calcium antagonist drug binding site in skeletal muscle sarcoplasmic reticulum: evidence for a calcium channel.

The sarcoplasmic reticulum (S.R.) of rabbit skeletal muscle has been found to contain a single, high affinity binding site for the Ca antagonist drug [3H]-nitrendipine. Two subfractions of the reticulum were studied, the heavy (HSR) and light (LSR) preparations, which exhibited similar nitrendipine equilibrium dissociation constants (KD) of 1nM. Crude cardiac and brain membranes assayed under the same conditions exhibited KD values of 0.2-0.3nM. The concentration of binding sites per mg. protein (Bmax) in HSR was found to be very high, namely 6.7 picomoles/mg, some four times greater than that of LSR. [3H]-nitrendipine binding to HSR was reversible and inhibited by the Ca antagonists flunarizine and verapamil, and by the intracellular Ca release antagonist TMB-8 (8-diethylamino-octyl 3,4,5-trimethylbenzoate hydrochloride). However, unlabelled nitrendipine at 2 X 10(-5)M had no effect on contraction of isolated electrically stimulated rabbit lumbrical or rat diaphragm muscles, nor did it affect the neuromuscular junction as studied in rat phrenic nerve-diaphragm preparations. Also, little effect of 2 X 10(-5)M nitrendipine was seen on net 45Ca uptake by HSR. These results suggest that [3H]-nitrendipine binding to skeletal muscle S.R. resembles that of brain membranes, which also contain a high affinity binding site for [3H]-nitrendipine and which similarly are pharmacologically insensitive to this dihydropyridine type of Ca channel blocking agent. Since HSR is also enriched in calsequestrin and terminal cysternae from which Ca is released in vivo, it seems likely that the [3H]-nitrendipine binding sites in S.R. are associated with Ca channels in the S.R.

Animals↗

Isolation of a calreticulin-like calcium binding protein from bovine brain.

Intracellular calcium levels are stringently regulated in all cells. The nature of this regulation is incompletely understood, but recent evidence indicates that the endoplasmic reticulum plays an important role in sequestering intracellular calcium. Using methods for isolating both calsequestrin and calreticulin, we have isolated a 58 kDa, high capacity calcium binding protein that exists in microsomes that shift their density in an oxalate-mediated density shift assay. This protein which we call CBP-58 bears similarities to the endoplasmic reticulum protein, calreticulin, in that it has a pI of 4.7 containing approximately 30% glutamate and aspartate, has a high capacity for calcium, and stains blue with the carbocyanine dye, 'Stains-all'. Peptide, amino acid, nucleotide and immunochemical analyses reveal further similarities between CBP-58 and calreticulin, but also some marked differences. Its tissue distribution suggests it is highly enriched in brain versus other tissues. We believe that CBP-58 is a calreticulin-like protein and that differences in the amino acid composition and sequences may reflect species diversity in calreticulin.

Amino Acid Sequence↗

Differences in the subcellular localization of calreticulin and organellar Ca(2+)-ATPase in neurons.

It has become clear that calcium is an important mediator in the transduction of signals due to ligand binding to cell surface receptors. Cytosolic calcium is typically maintained at low levels in both muscle and non-muscle cells and intracellular sequestering of calcium appears to be important in this process. The identification of intracellular calcium pools has been the subject of much recent study, and it has been proposed that such pools would contain three components: a calcium-activated pump or Ca(2+)-ATPase, a calcium channel such as the inositol trisphosphate receptor or ryanodine receptor, and a high-capacity calcium-binding protein such as calsequestrin or calreticulin. We report here on the localization of two components, the organellar Ca(2+)-ATPase (SERCA) and calreticulin, in neuronal tissues. Using immunofluorescence and subcellular fractionation, we have found that for the most part, these two proteins do not co-localize in neuron cell bodies, dendrites, or axons; but may co-localize at the axon terminal.

Animals↗

Comparative biochemical study of sarcolemma and sarcoplasmic reticulum fractions isolated from mouse skeletal and cardiac muscles.

1. Ca-ATPase activity, calcium-binding proteins and Concanavalin-A-bound glycoproteins of sarcolemma and sarcoplasmic reticulum were compared in mouse cardiac and skeletal muscles. 2. Ca-ATPase activity and calsequestrin were quite reduced in cardiac muscle, and the quantity of calcium bound to these two proteins was practically negligible, contrary to what was observed with skeletal muscle. In addition, the quantity of lipid bound calcium was not greater in cardiac muscle than in skeletal muscle. 3. Certain proteins seemed exclusively specific for skeletal muscle, including a 30,000 mol. wt glycoprotein which was totally absent in cardiac muscle sarcolemma.

Animals↗

Calreticulin expression in spinal motoneurons of the rat.

We have examined the expression of calreticulin in rat spinal motoneurons in order to reveal the occurrence and distribution of Ca2(+)-storage organelles in these neurons. Calreticulin, the non-muscle equivalent of calsequestrin, is the low-affinity, high-capacity calcium-binding protein responsible for intracompartmental Ca2(+)-storage in a number of different cell types. The results of the present immunohistochemical study show that all spinal motoneurons express calreticulin at approximately the same level; no significant differences in cytoplasmic immunostaining intensity were observed between different motoneuron pools or between small and large spinal motoneurons. Immunoelectron microscopy revealed that the intracellular localization of calreticulin within spinal motoneurons was confined to the endoplasmic reticulum and to spherical or pleiomorphic, frequently 'coated' vesicles with a diameter ranging between 120 and 150 nm. Some of these vesicles may represent the so-called calciosomes, the intracellular Ca2(+)-storage vesicles described in liver cells and in cerebellar Purkinje cells. The molecular components responsible for the uptake and release of Ca2+ from the Ca2(+)-storage organelles in spinal motoneurons still remain to be identified.

Animals↗

Skeletal muscle sarcoplasmic reticulum phenotype in myotonic dystrophy.

In this study we investigated the sarcoplasmic reticulum (SR), alongside myofibrillar phenotype, in muscle samples from five Myotonic Dystrophy (DM) patients and five control individuals. DM muscles exhibited as a common feature, a decrease in the slow isoform of myosin heavy chain (MHC) and of troponin C in myofibrils. We observed a match between myofibrillar changes and changes in SR membrane markers specific to fiber type, i.e. the fast (SERCA1) Ca(2+)-ATPase isoform increased concomitantly with a decrease of protein phospholamban (PLB), which in native SR membranes colocalizes with the slow (SERCA2a) SR Ca(2+)-ATPase, and regulates its activity depending on phosphorylation by protein kinases. Our results outline a cellular process selectively affecting slow-twitch fibers, and non-degenerative in nature, since neither the total number of Ca(2+)-pumps or of ryanodine receptor/Ca(2+)-release channels, or their ratio to the dihydropyridine receptor/voltage sensor in junctional transverse tubules, were found to be significantly changed in DM muscle. The only documented, apparently specific molecular changes associated with this process in the SR of DM muscle, are the defective expression of the slow/cardiac isoform of Ca(2+)-binding protein calsequestrin, together with an increased phosphorylation activity of membrane-bound 60 kDa Ca(2+)-calmodulin (CaM) dependent protein kinase. Enhanced phosphorylation of PLB by membrane-bound Ca(2+)-CaM protein kinase also appeared to be most pronounced in biopsy from a patient with a very high CTG expansion, as was the overall 'slow-to-fast' transformation of the same muscle biopsy. Animal studies showed that endogenous Ca(2+)-CaM protein kinase exerts a dual activatory role on SERCA2a SR Ca(2+)-ATPase, i.e. either by direct phosphorylation of the Ca(2+)-ATPase protein, or mediated by phosphorylation of PLB. Our results seem to be consistent with a maturational-related abnormality and/or with altered modulatory mechanisms of SR Ca(2+)-transport in DM slow-twitch muscle fibers.

Adolescent↗

Differential expression of the fast skeletal muscle proteome following chronic low-frequency stimulation.

Physiological and biochemical responses of skeletal muscle fibres to enhanced neuromuscular activity under conditions of maximum activation can be studied experimentally by chronic low-frequency stimulation of fast muscles. Stimulation-induced changes in the expression pattern of the rabbit fast skeletal muscle proteome were evaluated by two-dimensional gel electrophoresis and compared to the altered isoform expression profile of established transformation markers such as the Ca2+-ATPase, calsequestrin and the myosin heavy chain. Sixteen muscle proteins exhibited a marked change in their expression level. This included albumin with a 4-fold increase in abundance. In contrast, glycolytic enzymes, such as enolase and aldolase, showed a decreased expression. Concomitant changes were observed with marker elements of the contractile apparatus. While the fast isoforms of troponin T and myosin light chain 2 were drastically down-regulated, their slow counterparts exhibited increased expression. Interestingly, mitochondrial creatine kinase expression increased while the cytosolic isoform of this key muscle enzyme decreased. The expression of the small heat shock protein HSP-B5/alphaB-crystallin and the oxygen carrier protein myoglobin were both increased 2-fold following stimulation. The observed changes indicate that the conversion into fatigue-resistant red fibres depends on: (i) the optimum utilization of free fatty acids via albumin transportation, (ii) a rearrangement of the creatine kinase isozyme pattern for enhanced mitochondrial activity, (iii) an increased availability of oxygen for aerobic metabolism via myoglobin transport, (iv) the conversion of the contractile apparatus to isoforms with slower twitch characteristics and (v) the up-regulation of chaperone-like proteins for stabilising myofibrillar components during the fast-to-slow transition process.

Albumins↗

Microarray profiling of skeletal muscle sarcoplasmic reticulum proteins.

Microarrays were developed to profile the level of proteins associated with calcium regulation in sarcoplasmic reticulum (SR) isolated from porcine Longissimus muscle. The microarrays consisted of SR preparations printed onto to glass slides and probed with monoclonal antibodies to 7 target proteins. Proteins investigated included: ryanodine receptor, (RyR), dihydropyridine receptor, (DHPR), triadin (TRI), calsequestrin (CSQ), 90 kDa junctional protein (JSR90), and fast-twitch and slow-twitch SR calcium ATPases (SERCA1 and SERCA2). Signal from a fluorescently-labeled detection antibody was measured and quantitated using a slide reader. The microarray developed was also employed to profile Longissimus muscle SR proteins from halothane genotyped animals. Significant (P<0.05) reductions in levels of several proteins were found including: RyR, CSQ, TRI, DHPR and SERCA2 in SR samples from halothane positive animals. The results illustrate the potential of microarrays as a tool for profiling SR proteins and aiding investigations of calcium regulation.

Animals↗