Intense green‐, red‐emitting Tb3+, Tb3+/Bi3+‐doped and Sm3+, Sm3+/La3+‐doped Ca2Al2SiO7 phosphors

This paper focuses on an optical study of a Tb³⁺/Bi³⁺‐doped and Sm³⁺/La³⁺‐ doped Ca₂Al₂SiO₇ phosphor synthesized using combustion methods. Here, Ca₂Al₂SiO₇:Sm³⁺ showed a red emission band under visible light excitation but, when it co‐doped with La³⁺ ions, the emission intensity was further enhanced. Ca₂Al₂SiO₇:Tb³⁺ shows the characteristic green emission band under near‐ultraviolet light excitation wavelengths, co‐doping with Bi³⁺ ions produced enhanced photoluminescence intensity with better colour tunable properties. The phosphor exhibited better phase purity and crystallinity, confirmed by X‐ray diffraction. Binding energies of Ca(2p), Al(2p), Si(2p), O(1s) were studied using X‐ray photoelectron spectroscopy. The reported phosphor may be a promising visible light excited red phosphor for light‐emitting diodes and energy conversion devices.     

Nd3+‐Yb3+/Nd3+‐Yb3+‐Li+ co‐doped Gd2O3 phosphors for up and down conversion luminescence

Frequency up‐conversion (UC) emission from the Nd³⁺‐Yb³⁺/Nd³⁺‐Yb³⁺‐Li⁺ co‐doped gadolinium oxide (Gd₂O₃) phosphors prepared by the solution combustion technique in the visible range have been studied by using 980 nm near infrared (NIR) laser diode excitation. The crystalline structure and formation of the cubic phase has been confirmed with the help of X‐ray diffraction (XRD) studies. XRD peak shifts have been found towards the lower diffraction angle side in the case of the Nd³⁺‐Yb³⁺‐Li⁺ co‐doped phosphors. Surface morphology and particle size information have been observed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis. Down‐conversion emission study under 351 nm excitation in the visible region for the Nd³⁺‐Yb³⁺/Nd³⁺‐Yb³⁺‐Li⁺ co‐doped phosphors has been performed. The UC emission bands lying in the green and red region arising from the Nd³⁺ ions have been enhanced by ~260 times, ~113 times due to incorporation of Li⁺ ions in the Nd³⁺‐Yb³⁺ co‐doped phosphors. Photometric characterization has been done for the Nd³⁺‐Yb³⁺/Nd³⁺‐Yb³⁺‐Li⁺ co‐doped phosphors. The present study suggests the capability of the synthesized phosphors in near‐infrared (NIR) to visible upconverter and luminescent device applications.     

Novel Ca2+‐independent carbohydrate recognition of the C‐type lectins,SPL‐1 and SPL‐2, from the bivalve Saxidomus purpuratus

Novel Ca²⁺‐independent C‐type lectins, SPL‐1 and SPL‐2, were purified from the bivalve Saxidomus purpuratus. They are composed of dimers with either identical (SPL‐2 composed of two B‐chains) or distinct (SPL‐1 composed of A‐ and B‐chains) polypeptide chains, and show affinity for N‐acetylglucosamine (GlcNAc)‐ and N‐acetylgalactosamine (GalNAc)‐containing carbohydrates, but not for glucose or galactose. A database search for sequence similarity suggested that they belong to the C‐type lectin family. X‐ray crystallographic analysis revealed definite structural similarities between their subunits and the carbohydrate‐recognition domain (CRD) of the C‐type lectin family. Nevertheless, these lectins (especially SPL‐2) showed Ca²⁺‐independent binding affinity for GlcNAc and GalNAc. The crystal structure of SPL‐2/GalNAc complex revealed that bound GalNAc was mainly recognized via its acetamido group through stacking interactions with Tyr and His residues and hydrogen bonds with Asp and Asn residues, while widely known carbohydrate‐recognition motifs among the C‐type CRD (the QPD [Gln‐Pro‐Asp] and EPN [Glu‐Pro‐Asn] sequences) are not involved in the binding of the carbohydrate. Carbohydrate‐binding specificities of individual A‐ and B‐chains were examined by glycan array analysis using recombinant lectins produced from Escherichia coli cells, where both subunits preferably bound oligosaccharides having terminal GlcNAc or GalNAc with α‐glycosidic linkages with slightly different specificities.     

Inter‐subunit interaction of gastric H+,K+‐ATPase prevents reverse reaction of the transport cycle

The gastric H⁺,K⁺‐ATPase is an ATP‐driven proton pump responsible for generating a million‐fold proton gradient across the gastric membrane. We present the structure of gastric H⁺,K⁺‐ATPase at 6.5 Å resolution as determined by electron crystallography of two‐dimensional crystals. The structure shows the catalytic α‐subunit and the non‐catalytic β‐subunit in a pseudo‐E₂P conformation. Different from Na⁺,K⁺‐ATPase, the N‐terminal tail of the β‐subunit is in direct contact with the phosphorylation domain of the α‐subunit. This interaction may hold the phosphorylation domain in place, thus stabilizing the enzyme conformation and preventing the reverse reaction of the transport cycle. Indeed, truncation of the β‐subunit N‐terminus allowed the reverse reaction to occur. These results suggest that the β‐subunit N‐terminus prevents the reverse reaction from E₂P to E₁P, which is likely to be relevant for the generation of a large H⁺ gradient in vivo situation.     

Epigallocatechin‐3‐gallate induces mesothelioma cell death via H2O2−dependent T‐type Ca2+ channel opening

Malignant mesothelioma (MMe) is a highly aggressive, lethal tumour requiring the development of more effective therapies. The green tea polyphenol epigallocathechin‐3‐gallate (EGCG) inhibits the growth of many types of cancer cells. We found that EGCG is selectively cytotoxic to MMe cells with respect to normal mesothelial cells. MMe cell viability was inhibited by predominant induction of apoptosis at lower doses and necrosis at higher doses. EGCG elicited H₂O₂ release in cell cultures, and exogenous catalase (CAT) abrogated EGCG‐induced cytotoxicity, apoptosis and necrosis. Confocal imaging of fluo 3‐loaded, EGCG‐exposed MMe cells showed significant [Ca²⁺]_i rise, prevented by CAT, dithiothreitol or the T‐type Ca²⁺ channel blockers mibefradil and NiCl₂. Cell loading with dihydrorhodamine 123 revealed EGCG‐induced ROS production, prevented by CAT, mibefradil or the Ca²⁺ chelator BAPTA‐AM. Direct exposure of cells to H₂O₂ produced similar effects on Ca²⁺ and ROS, and these effects were prevented by the same inhibitors. Sensitivity of REN cells to EGCG was correlated with higher expression of Ca_v3.2 T‐type Ca²⁺ channels in these cells, compared to normal mesothelium. Also, Ca_v3.2 siRNA on MMe cells reduced in vitro EGCG cytotoxicity and abated apoptosis and necrosis. Intriguingly, Ca_v3.2 expression was observed in malignant pleural mesothelioma biopsies from patients, but not in normal pleura. In conclusion, data showed the expression of T‐type Ca²⁺ channels in MMe tissue and their role in EGCG selective cytotoxicity to MMe cells, suggesting the possible use of these channels as a novel MMe pharmacological target.     

Conductive Li3.08Cr0.02Si0.09V0.9O4 Anode Material: Novel “Zero‐Strain” Characteristic and Superior Electrochemical Li+ Storage

“Zero‐strain” compounds are ideal energy‐storage materials for long‐term cycling because they present negligible volume change and significantly reduce the mechanically induced deterioration during charging–discharging. However, the explored “zero‐strain” compounds are very limited, and their energy densities are low. Here, γ phase Li_3.08Cr_0.02Si_0.09V_0.9O₄ (γ‐LCSVO) is explored as an anode compound for lithium‐ion batteries, and surprisingly its “zero‐strain” Li⁺ storage during Li⁺ insertion–extraction is found through using various state‐of‐the‐art characterization techniques. Li⁺ sequentially inserts into the 4c(1) and 8d sites of γ‐LCSVO, but its maximum unit‐cell volume variation is only ≈0.18%, the smallest among the explored “zero‐strain” compounds. Its mean strain originating from Li⁺ insertion is only 0.07%. Consequently, both γ‐LCSVO nanowires (γ‐LCSVO‐NW) and micrometer‐sized particles (γ‐LCSVO‐MP) exhibit excellent cycling stability with 90.1% and 95.5% capacity retention after as long as 2000 cycles at 10C, respectively. Moreover, γ‐LCSVO‐NW and γ‐LCSVO‐MP respectively deliver large reversible capacities of 445.7 and 305.8 mAh g^?1 at 0.1C, and retain 251.2 and 78.4 mAh g^?1 at 10C. Additionally, γ‐LCSVO shows a suitably safe operating potential of ≈1.0 V, significantly lower than that of the famous “zero‐strain” Li₄Ti₅O₁₂ (≈1.6 V). These merits demonstrate that γ‐LCSVO can be a practical anode compound for stable, high‐energy, fast‐charging, and safe Li⁺ storage.     

Ca2+‐dependent down‐regulation of human histamine H1 receptors in Chinese hamster ovary cells

G_q/11 protein‐coupled human histamine H₁ receptors in Chinese hamster ovary cells stimulated with histamine undergo clathrin‐dependent endocytosis followed by proteasome/lysosome‐mediated down‐regulation. In this study, we evaluated the effects of a sustained increase in intracellular Ca²⁺ concentrations induced by a receptor‐bypassed stimulation with ionomycin, a Ca²⁺ ionophore, on the endocytosis and down‐regulation of H₁ receptors in Chinese hamster ovary cells. All cellular and cell‐surface H₁ receptors were detected by the binding of [³H]mepyramine to intact cells sensitive to the hydrophobic and hydrophilic H₁ receptor ligands, mepyramine and pirdonium, respectively. The pretreatment of cells with ionomycin markedly reduced the mepyramine‐ and pirdonium‐sensitive binding sites of [³H]mepyramine, which were completely abrogated by the deprivation of extracellular Ca²⁺ and partially by a ubiquitin‐activating enzyme inhibitor (UBEI‐41), but were not affected by inhibitors of calmodulin (W‐7 or calmidazolium) and protein kinase C (chelerythrine or GF109203X). These ionomycin‐induced changes were also not affected by inhibitors of receptor endocytosis via clathrin (hypertonic sucrose) and caveolae/lipid rafts (filipin or nystatin) or by inhibitors of lysosomes (E‐64, leupeptin, chloroquine, or NH₄Cl), proteasomes (lactacystin or MG‐132), and a Ca²⁺‐dependent non‐lysosomal cysteine protease (calpain) (MDL28170). Since H₁ receptors were normally detected by confocal immunofluorescence microscopy with an antibody against H₁ receptors, even after the ionomycin treatment, H₁ receptors appeared to exist in a form to which [³H]mepyramine was unable to bind. These results suggest that H₁ receptors are apparently down‐regulated by a sustained increase in intracellular Ca²⁺ concentrations with no process of endocytosis and lysosomal/proteasomal degradation of receptors.

     

Breaking up and making up: The secret life of the vacuolar H+‐ATPase

The vacuolar ATPase (V‐ATPase; V₁V_o‐ATPase) is a large multisubunit proton pump found in the endomembrane system of all eukaryotic cells where it acidifies the lumen of subcellular organelles including lysosomes, endosomes, the Golgi apparatus, and clathrin‐coated vesicles. V‐ATPase function is essential for pH and ion homeostasis, protein trafficking, endocytosis, mechanistic target of rapamycin (mTOR), and Notch signaling, as well as hormone secretion and neurotransmitter release. V‐ATPase can also be found in the plasma membrane of polarized animal cells where its proton pumping function is involved in bone remodeling, urine acidification, and sperm maturation. Aberrant (hypo or hyper) activity has been associated with numerous human diseases and the V‐ATPase has therefore been recognized as a potential drug target. Recent progress with moderate to high‐resolution structure determination by cryo electron microscopy and X‐ray crystallography together with sophisticated single‐molecule and biochemical experiments have provided a detailed picture of the structure and unique mode of regulation of the V‐ATPase. This review summarizes the recent advances, focusing on the structural and biophysical aspects of the field.     

H2O2 in plant peroxisomes: an in vivo analysis uncovers a Ca2+‐dependent scavenging system

Oxidative stress is a major challenge for all cells living in an oxygen‐based world. Among reactive oxygen species, H₂O₂, is a well known toxic molecule and, nowadays, considered a specific component of several signalling pathways. In order to gain insight into the roles played by H₂O₂ in plant cells, it is necessary to have a reliable, specific and non‐invasive methodology for its in vivo detection. Hence, the genetically encoded H₂O₂ sensor HyPer was expressed in plant cells in different subcellular compartments such as cytoplasm and peroxisomes. Moreover, with the use of the new green fluorescent protein (GFP)‐based Cameleon Ca²⁺ indicator, D3cpv–KVK–SKL, targeted to peroxisomes, we demonstrated that the induction of cytoplasmic Ca²⁺ increase is followed by Ca²⁺ rise in the peroxisomal lumen. The analyses of HyPer fluorescence ratios were performed in leaf peroxisomes of tobacco and pre‐ and post‐bolting Arabidopsis plants. These analyses allowed us to demonstrate that an intraperoxisomal Ca²⁺ rise in vivo stimulates catalase activity, increasing peroxisomal H₂O₂ scavenging efficiency.     

Structural characterization of Er3+,Yb3+‐doped Gd2O3 phosphor,synthesized using the solid‐state reaction method,and its luminescence behavior

We report the synthesis and structural characterization of Er³⁺,Yb³⁺‐doped Gd₂O₃ phosphor. The sample was prepared using the conventional solid‐state reaction method, which is the most suitable method for large‐scale production. The prepared phosphor sample was characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermoluminescence (TL), photoluminescence (PL) and CIE techniques. For PL studies, the excitation and emission spectra of Gd₂O₃ phosphor doped with Er³⁺ and Yb³⁺ were recorded. The excitation spectrum was recorded at a wavelength of 551 nm and showed an intense peak at 276 nm. The emission spectrum was recorded at 276 nm excitation and showed peaks in all blue, green and red regions, which indicate that the prepared phosphor may act as a single host for white light‐emitting diode (WLED) applications, as verified by International de I'Eclairage (CIE) techniques. From the XRD data, the calculated average crystallite size of Er³⁺ and Yb³⁺‐doped Gd₂O₃ phosphor is ~ 38 nm. A TL study was carried out for the phosphor using UV irradiation. The TL glow curve was recorded for UV, beta and gamma irradiations, and the kinetic parameters were also calculated. In addition, the trap parameters of the prepared phosphor were also studied using computerized glow curve deconvolution (CGCD). Copyright © 2015 John Wiley & Sons, Ltd.     

Improved oxidative tolerance in suspension‐cultured cells of C_4-pepctransgenic rice by H_2O_2 and Ca~(2+)under PEG-6000

To understand the molecular responses of PC(Overexpressing the maize C4-pepc gene, which encodes phosphoenolpyruvate carboxylase(PEPC)), to drought stress at cell level, we analyzed changes in the levels of signaling molecules(hydrogen peroxide(H2O2), calcium ion(Ca2t), and nitric oxide(NO)) in suspension-cultured PC and wild-type(WT)rice(Oryza sativa L.) cell under drought stress induced by 20%polyethylene glycol 6000(PEG-6000). Results demonstrated that PC improved drought tolerance by enhancing antioxidant defense, retaining higher relative water content, survival percentages, and dry weight of cells. In addition, PEPC activity in PC under PEG treatment was strengthened by addition of H2O2 inhibitor, dimethylthiourea(DMTU) and NO synthesis inhibitor, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(c PTIO), respectively, while that in PC was weakened by addition of free calcium chelator, ethylene glycol-bis(b-aminoethylether)-N,N,N0,N0-tetraacetic acid(EGTA)t calcium channel outflow inhibitor, ruthenium red(RR) t plasma membrane channel blocker La(NO3)3, but EGTA t RR did Reseanot. Results also showed that NO and Ca2 twas lying downstream of H2O2 in drought-induced signaling. Calcium ion was also involved in the expression of C4-pepc in PC. These results suggested that PC could improve oxidative tolerance in suspension-cultured cells and the acquisition of this tolerance required downregulation of H2O2 and the entry of extracellular Ca2 tinto cells across the plasma membrane for regulation of PEPC activity and C4-pepc expression.     

Cellular localization of the K+‐dependent Na+–Ca2+ exchanger NCKX5 and the role of the cytoplasmic loop in its distribution in pigmented cells

NCKX5 is a bidirectional K⁺‐dependent Na⁺–Ca²⁺ exchanger, which belongs to the SLC24A gene family. In particular, the A111T mutation of NCKX5 has been associated with reduced pigmentation in European populations. In contrast to other NCKX isoforms, which function in the plasma membrane (PM), NCKX5 has been shown to localize either in the trans‐Golgi network (TGN) or in melanosomes. Moreover, sequences responsible for retaining its intracellular localization are unknown. This study addresses two major questions: (i) clarification of intracellular location of NCKX5 and (ii) identification of sequences that retain NCKX5 inside the cell. We designed a set of cDNA constructs representing NCKX5 loop deletion mutants and NCKX2–NCKX5 chimeras to address these two questions after expression in pigmented MNT1 cells. Our results show that NCKX5 is not a PM resident and is exclusively located in the TGN. Moreover, the large cytoplasmic loop is the determinant for retaining NCKX5 in the TGN.     

Luminescence and energy transfer in Ce3+, Mn2+‐doped K2AEP2O7 (AE = Ca,Sr) phosphor

Pyrophosphates K₂AEP₂O₇ (AE = Ca, Sr) prepared by the classical solid‐state technique and activated with Ce³⁺ are described. Intense emission was observed in K₂AEP₂O₇ (AE = Ca, Sr). The effect of Mn²⁺ co‐doping was studied. The broad emission peak of Mn²⁺ was observed at 534 nm in K₂SrP₂O₇:Ce³⁺ and at 539 nm in K₂CaP₂O₇:Ce³⁺, Mn²⁺. Mn²⁺ emission was greatly enhanced by addition of the sensitizer Ce³⁺ due to efficient energy transfer from Ce³⁺ to Mn²⁺. Copyright © 2015 John Wiley & Sons, Ltd.