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Ca2+ Binding (ca2+ + binding)
Terms modified by Ca2+ Binding Selected AbstractsSpecific Ca2+ Fluorescent Sensor: Signaling by Conformationally Induced PET Suppression in a Bichromophoric AcridinedioneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 34 2009Pichandi Ashokkumar Abstract A series of acridinedione-based bichromophoric podand systems 1a,c were synthesized and characterized. Among these, bichromophore 1c shows specific binding of Ca2+ in the presence of other biologically important metal ions like Na+, K+, Mg2+, and Zn2+. The selective complexation was proved by steady-state emission, time-resolved emission, and 1H NMR titration. Signaling of the binding event was achieved by Ca2+ -induced folding of the bichromophore, resulting in PET suppression in the acridinedione chromophore. Involvement of a PET process in the optical signaling was confirmed by comparing bichromophores 1a,c with non-PET compound 2 and monochromophore model compound 3. Non-PET compound 2 failed to give optical response upon Ca2+ binding as a result of the absence of a PET process in the Ca2+ -bound complex. Monochromophore 3 shows a similar optical response, which is the same as that in 1c. Titration of the metal-ion-bound complex of 1c with EDTA released the metal ion from the complex, thereby regaining the original photophysical properties of the bichromophore.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Irregular dimerization of guanylate cyclase-activating protein 1 mutants causes loss of target activationFEBS JOURNAL, Issue 18 2004Ji-Young Hwang Guanylate cyclase-activating proteins (GCAPs) are neuronal calcium sensors that activate membrane bound guanylate cyclases (EC 4.6.1.2.) of vertebrate photoreceptor cells when cytoplasmic Ca2+ decreases during illumination. GCAPs contain four EF-hand Ca2+ -binding motifs, but the first EF-hand is nonfunctional. It was concluded that for GCAP-2, the loss of Ca2+ -binding ability of EF-hand 1 resulted in a region that is crucial for targeting guanylate cyclase [Ermilov, A.N., Olshevskaya, E.V. & Dizhoor, A.M. (2001) J. Biol. Chem.276, 48143,48148]. In this study we tested the consequences of mutations in EF-hand 1 of GCAP-1 with respect to Ca2+ binding, Ca2+ -induced conformational changes and target activation. When the nonfunctional first EF-hand in GCAP-1 is replaced by a functional EF-hand the chimeric mutant CaM,GCAP-1 bound four Ca2+ and showed similar Ca2+ -dependent changes in tryptophan fluorescence as the wild-type. CaM,GCAP-1 neither activated nor interacted with guanylate cyclase. Size exclusion chromatography revealed that the mutant tended to form inactive dimers instead of active monomers like the wild-type. Critical amino acids in EF-hand 1 of GCAP-1 are cysteine at position 29 and proline at position 30, as changing these to glycine was sufficient to cause loss of target activation without a loss of Ca2+ -induced conformational changes. The latter mutation also promoted dimerization of the protein. Our results show that EF-hand 1 in wild-type GCAP-1 is critical for providing the correct conformation for target activation. [source] Inhibition of SERCA Ca2+ pumps by 2-aminoethoxydiphenyl borate (2-APB)FEBS JOURNAL, Issue 15 20022-APB reduces both Ca2+ binding, by interfering with the pathway leading to the Ca2+ -binding sites, phosphoryl transfer from ATP 2-Aminoethoxydiphenyl Borate (2-APB) has been extensively used recently as a membrane permeable modulator of inositol-1,4,5-trisphosphate-sensitive Ca2+ channels and store-operated Ca2+ entry. Here, we report that 2-APB is also an inhibitor of sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA) Ca2+ pumps, and additionally increases ion leakage across the phospholipid bilayer. Therefore, we advise caution in the interpretation of results when used in Ca2+ signalling experiments. The inhibition of 2-APB onthe SERCA Ca2+ pumps is isoform-dependent, with SERCA 2B being more sensitive than SERCA 1A (IC50 values for inhibition being 325 and 725 µm, respectively, measured at pH 7.2). The Ca2+ -ATPase is also more potently inhibited at lower pH (IC50 = 70 µm for SERCA1A at pH 6). 2-APB decreases the affinity for Ca2+ binding to the ATPase by more than 20-fold, and also inhibits phosphoryl transfer from ATP (by 35%), without inhibiting nucleotide binding. Activity studies performed using mutant Ca2+ -ATPases show that Tyr837 is critical for the inhibition of activity by 2-APB. Molecular modeling studies of 2-APB binding to the Ca2+ ATPase identified two potential binding sites close to this residue, near or between transmembrane helices M3, M4, M5 and M7. The binding of 2-APB to these sites could influence the movement of the loop between M6 and M7 (L6-7), and reduce access of Ca2+ to their binding sites. [source] Electroaddressing of Cell Populations by Co-Deposition with Calcium Alginate HydrogelsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Xiao-Wen Shi Abstract Electroaddressing of biological components at specific device addresses is attractive because it enlists the capabilities of electronics to provide spatiotemporally controlled electrical signals. Here, the electrodeposition of calcium alginate hydrogels at specific electrode addresses is reported. The method employs the low pH generated at the anode to locally solubilize calcium ions from insoluble calcium carbonate. The solubilized Ca2+ can then bind alginate to induce this polysaccharide to undergo a localized sol-gel transition. Calcium alginate gel formation is shown to be spatially controlled in the normal and lateral dimensions. The deposition method is sufficiently benign that it can be used to entrap the bacteria E. coli. The entrapped cells are able to grow and respond to chemical inducers in their environment. Also, the entrapped cells can be liberated from the gel network by adding sodium citrate that can compete with alginate for Ca2+ binding. The capabilities of calcium alginate electrodeposition is illustrated by entrapping reporter cells that can recognize the quorum sensing autoinducer 2 (AI-2) signaling molecule. These reporter cells were observed to recognize and respond to AI-2 generated from an external bacterial population. Thus, calcium alginate electrodeposition provides a programmable method for the spatiotemporally controllable assembly of cell populations for cell-based biosensing and for studying cell-cell signaling. [source] Interaction of heparin with Ca2+: A model study with a synthetic heparin-like hexasaccharideISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2000Jesús Angulo The binding of Ca2+ to synthetic hexasaccharide 1, containing the structural motifs of the regular region of heparin, has been investigated using NMR spectroscopy and molecular modeling. The NMR data of the calcium salt of 1 indicate the existence of specific Ca2+ binding, and molecular modeling results predict three different types of binding sites with different negative potential and preorganized geometry. The presence of Ca2+ does not seem to affect the overall helical structure of hexasaccharide 1, although it seems to have a marked influence on the flexibility of the oligosaccharide backbone. [source] A classification of the fibrin network structures formed from the hereditary dysfibrinogensJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 8 2006T. SUGO Summary.,Objective: The main objective was to study the relationships of the molecular defects in 38 dysfibrinogens with their fibrin networks. Methods and results: Scanning electron microscopic analyses revealed that all the fibrins formed under the same conditions had networks composed of either normal thickness fibers or thin fibers, accompanied by a variety of alterations in the network structure and characteristics. We classified these fibrin networks into five classes, designated normal, less-ordered, porous A, porous B and lace-like networks. The dysfibrinogens with defects in fibrinopeptide A release or the E:D binding sites formed normal or less-ordered networks, while those with defects in the D:D association formed porous A networks composed of many tapered terminating fibers, despite having fibers of normal width, and containing many pores or spaces. The porous B and lace-like networks were composed of highly branched thin fibers because of defects in the lateral association among protofibrils, and the major difference between them was the porosity of the porous B networks. All the porous B networks were easily damaged by mechanical stress, whereas the lace-like networks retained high resistance to such stress, indicating that the network strength was not dependent on the fiber width, but on the porosity that led to fragility of the network. Conclusion: Impairment of the D:D association is the major disturbing factor that leads to the formation of porous fibrin networks. The porosity may be introduced by severe impairment of the D:D association, as well as the lateral association, as has often been observed by extra glycosylation or defects in Ca2+ binding. [source] Ca2+ -dependent inactivation of Ca2+ -induced Ca2+ release in bullfrog sympathetic neuronsTHE JOURNAL OF PHYSIOLOGY, Issue 14 2008Tenpei Akita We studied inactivation of Ca2+ -induced Ca2+ release (CICR) via ryanodine receptors (RyRs) in bullfrog sympathetic neurons. The rate of rise in [Ca2+]i due to CICR evoked by a depolarizing pulse decreased markedly within 10,20 ms to a much slower rate despite persistent Ca2+ entry and little depletion of Ca2+ stores. The Ca2+ entry elicited by the subsequent pulse within 50 ms, during which the [Ca2+]i level remained unchanged, did not generate a distinct [Ca2+]i rise. This mode of [Ca2+]i rise was unaffected by a mitochondrial uncoupler, carbonyl cyanide p -trifluromethoxy-phenylhydrazone (FCCP, 1 ,m). Paired pulses of varying interval and duration revealed that recovery from inactivation became distinct , 50 ms after depolarization and depended on [Ca2+]i. The inactivation was prevented by BAPTA (, 100 ,m) but not by EGTA (, 10 mm), whereas the activation was less affected by BAPTA. When CICR was partially activated, some of the non-activated RyRs were also inactivated directly. Thus, the inactivation in these neurons is induced by Ca2+ binding to the high-affinity regulatory sites residing very close to Ca2+ channels and/or RyRs, although the sites for activation are located much closer to those Ca2+ sources. The rate of [Ca2+]i decay after the pulse decreased with increasing pulse duration longer than 10 ms, and this was abolished by BAPTA. Thus, some mechanism counteracting Ca2+ clearance is induced after full inactivation and potentiated during the pulse. Possible models for RyR inactivation were proposed and the roles of inactivation in Ca2+ signalling were discussed. 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