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991.
Stefan Schorr Marie-Christine Klein Igor Gamayun Armin Melnyk Martin Jung Nico Sch?uble Qian Wang Birgit Hemmis Florian Bochen Markus Greiner Pavel Lampel Sabine Katharina Urban Sarah Hassdenteufel Johanna Dudek Xing-Zhen Chen Richard Wagner Adolfo Cavalié Richard Zimmermann 《The Journal of biological chemistry》2015,290(30):18621-18635
In mammalian cells, signal peptide-dependent protein transport into the endoplasmic reticulum (ER) is mediated by a dynamic polypeptide-conducting channel, the heterotrimeric Sec61 complex. Previous work has characterized the Sec61 complex as a potential ER Ca2+ leak channel in HeLa cells and identified ER lumenal molecular chaperone immunoglobulin heavy-chain-binding protein (BiP) as limiting Ca2+ leakage via the open Sec61 channel by facilitating channel closing. This BiP activity involves binding of BiP to the ER lumenal loop 7 of Sec61α in the vicinity of tyrosine 344. Of note, the Y344H mutation destroys the BiP binding site and causes pancreatic β-cell apoptosis and diabetes in mice. Here, we systematically depleted HeLa cells of the BiP co-chaperones by siRNA-mediated gene silencing and used live cell Ca2+ imaging to monitor the effects on ER Ca2+ leakage. Depletion of either one of the ER lumenal BiP co-chaperones, ERj3 and ERj6, but not the ER membrane-resident co-chaperones (such as Sec63 protein, which assists BiP in Sec61 channel opening) led to increased Ca2+ leakage via Sec6 complex, thereby phenocopying the effect of BiP depletion. Thus, BiP facilitates Sec61 channel closure (i.e. limits ER Ca2+ leakage) via the Sec61 channel with the help of ERj3 and ERj6. Interestingly, deletion of ERj6 causes pancreatic β-cell failure and diabetes in mice and humans. We suggest that co-chaperone-controlled gating of the Sec61 channel by BiP is particularly important for cells, which are highly active in protein secretion, and that breakdown of this regulatory mechanism can cause apoptosis and disease. 相似文献
992.
Camillo Peracchia Kate C. Young Xiao G. Wang Joey T. Chen Lillian L. Peracchia 《Cell communication & adhesion》2003,10(4):233-237
Cx45 channel sensitivity to CO2, transjunctional voltage (Vj) and inhibition of calmodulin (CaM) expression was tested in oocytes by dual voltage-clamp. Cx45 channels are very sensitive to Vj and close preferentially by the slow gate, likely the same as the chemical gate. With CO2-induced drop in junctional conductance (Gj), the speed of Vj-dependent inactivation of junctional current (Ij) and Vj sensitivity increased. With 40 mV Vj, the τ of single exponential Ij decay reversibly decreased by ∼40% with CO2, and Gj steady state/Gj peak decreased multiphasically, indicating that kinetics and Vj sensitivity of chemical/slow-Vj gating are altered by changes in [H+]i and/or [Ca2+]i. With 15 min exposure to CO2, Gj dropped to 0% in controls and by ∼17% following CaM expression inhibition; similarly, Vj sensitivity decreased significantly. This indicates that the speed and sensitivity of Vj-dependent inactivation of Cx45 channels are increased by CO2, and that CaM plays a role in gating. Cx32 channels behaved similarly, but the drop in both Gj steady state/Gj peak and τ with CO2 matched more closely that of Gj peak. In contrast, sensitivity and speed of Vj gating of Cx40 and Cx26 channels decreased, rather than increased, with CO2 application. 相似文献
993.
Annette Stange Rainer Hedrich M. Rob G. Roelfsema 《The Plant journal : for cell and molecular biology》2010,62(2):265-276
Rapid stomatal closure is driven by the activation of S‐type anion channels in the plasma membrane of guard cells. This response has been linked to Ca2+ signalling, but the impact of transient Ca2+ signals on S‐type anion channel activity remains unknown. In this study, transient elevation of the cytosolic Ca2+ level was provoked by voltage steps in guard cells of intact Nicotiana tabacum plants. Changes in the activity of S‐type anion channels were monitored using intracellular triple‐barrelled micro‐electrodes. In cells kept at a holding potential of ?100 mV, voltage steps to ?180 mV triggered elevation of the cytosolic free Ca2+ concentration. The increase in the cytosolic Ca2+ level was accompanied by activation of S‐type anion channels. Guard cell anion channels were activated by Ca2+ with a half maximum concentration of 515 nm (SE = 235) and a mean saturation value of ?349 pA (SE = 107) at ?100 mV. Ca2+ signals could also be evoked by prolonged (100 sec) depolarization of the plasma membrane to 0 mV. Upon returning to ?100 mV, a transient increase in the cytosolic Ca2+ level was observed, activating S‐type channels without measurable delay. These data show that cytosolic Ca2+ elevation can activate S‐type anion channels in intact guard cells through a fast signalling pathway. Furthermore, prolonged depolarization to 0 mV alters the activity of Ca2+ transport proteins, resulting in an overshoot of the cytosolic Ca2+ level after returning the membrane potential to ?100 mV. 相似文献
994.
Takuya Furuichi Takayuki Sasaki Yoshiyuki Tsuchiya Peter R. Ryan Emmanuel Delhaize Yoko Yamamoto 《The Plant journal : for cell and molecular biology》2010,64(1):47-55
Al3+‐resistant cultivars of wheat (Triticum aestivum L.) release malate through the Al3+‐activated anion transport protein Triticum aestivum aluminum‐activated malate transporter 1 (TaALMT1). Expression of TaALMT1 in Xenopus oocytes and tobacco suspension cells enhances the basal transport activity (inward and outward currents present in the absence of external Al3+), and generates the same Al3+‐activated currents (reflecting the Al3+‐dependent transport function) as observed in wheat cells. We investigated the amino acid residues involved in this Al3+‐dependent transport activity by generating a series of mutations to the TaALMT1 protein. We targeted the acidic residues on the hydrophilic C‐terminal domain of TaALMT1 and changed them to uncharged residues by site‐directed mutagenesis. These mutant proteins were expressed in Xenopus oocytes and their transport activity was measured before and after Al3+ addition. Three mutations (E274Q, D275N and E284Q) abolished the Al3+‐activated transport activity without affecting the basal transport activity. Truncation of the hydrophilic C‐terminal domain abolished both basal and Al3+‐activated transport activities. Al3+‐dependent transport activity was recovered by fusing the N‐terminal region of TaALMT1 with the C‐terminal region of AtALMT1, a homolog from Arabidopsis. These findings demonstrate that the extracellular C‐terminal domain is required for both basal and Al3+‐dependent TaALMT1 activity. Furthermore, we identified three acidic amino acids within this domain that are specifically required for the activation of transport function by external Al3+. 相似文献
995.
Model of the outer membrane potential generation by the inner membrane of mitochondria. 总被引:6,自引:0,他引:6
Victor V Lemeshko 《Biophysical journal》2002,82(2):684-692
Voltage-dependent anion channels in the outer mitochondrial membrane are strongly regulated by electrical potential. In this work, one of the possible mechanisms of the outer membrane potential generation is proposed. We suggest that the inner membrane potential may be divided on two resistances in series, the resistance of the contact sites between the inner and outer membranes and the resistance of the voltage-dependent anion channels localized beyond the contacts in the outer membrane. The main principle of the proposed mechanism is illustrated by simplified electric and kinetic models. Computational behavior of the kinetic model shows a restriction of the steady-state metabolite flux through the mitochondrial membranes at relatively high concentration of the external ADP. The flux restriction was caused by a decrease of the voltage across the contact sites and by an increase in the outer membrane potential (up to +60 mV) leading to the closure of the voltage-dependent anion channels localized beyond the contact sites. This mechanism suggests that the outer membrane potential may arrest ATP release through the outer membrane beyond the contact sites, thus tightly coordinating mitochondrial metabolism and aerobic glycolysis in tumor and normal proliferating cells. 相似文献
996.
高压静电对烟草愈伤组织生长和根分化的效应 总被引:6,自引:0,他引:6
用场强 +1.0 KV/ cm高压静电 ( HV EF)处理烟草愈伤组织 30 min,处理组愈伤组织生长量达 10 .6 4g,比对照组高 8.0 % ,根分化率达 70 .6 % ,比对照组高 95%。超氧物歧化酶 ( SOD)活性、蛋白质含量分别为356 .3U/ g.FW、11.0 7m g/ g.FW,分别比对照增加 10 .5%、2 3.5%。过氧化物酶 ( POD)和吲哚乙酸 ( IAA)氧化酶活性处理组分别为 56 .3OD4 70 / min.g.FW、87.1μg/ g.h.FW,分别比对照下降 2 6 .1%、8.7%。结果表明 ,高压静电处理可促进烟草愈伤组织细胞生长和根的分化 ,这与 HV EF影响体内 SOD、POD和 IAA氧化酶活性以及蛋白质含量的变化相关。 相似文献
997.
Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies 下载免费PDF全文
Vasileios C. Nikolis Johannes Benduhn Felix Holzmueller Fortunato Piersimoni Matthias Lau Olaf Zeika Dieter Neher Christian Koerner Donato Spoltore Koen Vandewal 《Liver Transplantation》2017,7(21)
High photon energy losses limit the open‐circuit voltage (VOC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the VOC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha‐sexithiophene (α‐6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the VOC of an α‐6T/SubNc/SubPc fullerene‐free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D–A interface. By accurately measuring the optical gap (Eopt) and the energy of the charge‐transfer state (ECT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. Eopt – qVOC losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the VOC‐optimized devices, the low‐energy (700 nm) external quantum efficiency (EQE) peak remains high at 79%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low‐voltage losses can be combined with a high EQE in organic photovoltaic devices. 相似文献
998.
Takashi Hasegawa Hironori Miyata Keita Nishi Akira Sagari Takefumi Moriuchi Takashi Matsuo 《Somatosensory & motor research》2017,34(3):151-157
Purpose Vivid motor imagery appears to be associated with improved motor learning efficiency. However, the practical difficulties in measuring vivid motor imagery warrant new analytical approaches. The present study aimed to determine the instruction conditions for which vividness in motor imagery could be more easily seen and the excitability of the sensory cortex as it relates to the motor image. Materials and methods In total, 15 healthy, right-handed volunteers were instructed to imagine grasping a rubber ball under a verbal-only instruction condition (verbal condition), a verbal?+?visual instruction condition (visual condition), and a verbal?+?execution (physically grasping a real ball) condition (execution condition). We analyzed motor imagery-related changes in somatosensory cortical excitability by comparing somatosensory-evoked potentials in each condition with the rest (control) condition. We also used a visual analogue scale to measure subject-reported vividness of imagery. Results We found the N33 component was significantly lower in the execution condition than in the rest condition (p?0.05). The results suggested a gating effect via central efferent mechanisms that affected the excitability of areas 3b or 1 in the primary somatosensory cortex, but only in the execution condition. Conclusions These data suggest that experiencing a movement through actual motor execution immediately prior to performing mental imagery of that movement enhances the excitability of motor-related cortical areas. It is suggested that the excitability of the motor-related region increased as a result of the motor imagery in the execution condition acting on the corresponding somatosensory cortex. 相似文献
999.
1000.
Oxygenated CdS Buffer Layers Enabling High Open‐Circuit Voltages in Earth‐Abundant Cu2BaSnS4 Thin‐Film Solar Cells 下载免费PDF全文
Jie Ge Prakash Koirala Corey R. Grice Paul J. Roland Yue Yu Xinxuan Tan Randy J. Ellingson Robert W. Collins Yanfa Yan 《Liver Transplantation》2017,7(6)
Earth‐abundant Cu2BaSnS4 (CBTS) thin films exhibit a wide bandgap of 2.04–2.07 eV, a high absorption coefficient > 104 cm?1, and a p‐type conductivity, suitable as a top‐cell absorber in tandem solar cell devices. In this work, sputtered oxygenated CdS (CdS:O) buffer layers are demonstrated to create a good p–n diode with CBTS and enable high open‐circuit voltages of 0.9–1.1 V by minimizing interface recombination. The best power conversion efficiency of 2.03% is reached under AM 1.5G illumination based on the configuration of fluorine‐doped SnO2 (back contact)/CBTS/CdS:O/CdS/ZnO/aluminum‐doped ZnO (front contact). 相似文献