Home About us Contact
|
Home About us Contact | ||
|
|
||
Motive Force (motive + force)
Kinds of Motive Force Selected AbstractsCold-Induced Recruitment of Brown Adipose Tissue ThermogenesisEXPERIMENTAL PHYSIOLOGY, Issue 1 2003Martin Klingenspor Non-shivering thermogenesis in brown adipose tissue is the main mechanism for thermoregulatory heat production in small mammals and newborns. During cold acclimation the sympathetic innervation triggers the recruitment of brown adipose tissue by hyperplasia, which involves the proliferation and differentiation of precursor cells, and by hypertrophy of mature brown adipocytes. Mitochondrial biogenesis and increased synthesis of the uncoupling protein 1 (UCP-1) are hallmarks of the thermogenic recruitment process. The severalfold increase of mitochondrial protein content during cold acclimation recruits a large capacity for oxidative phosphorylation. However, UCP-1 increases proton leakage across the inner membrane of brown adipocyte mitochondria and thereby dissipates proton motive force as heat instead of ATP synthesis. During recent years considerable progress has been achieved in the analysis of transcriptional mechanisms controlling Ucp1 gene expression. However, so far only little is known about the molecular basis of cold-induced mitochondrial biogenesis in brown adipose tissue. [source] Contribution of exofacial thiol groups in the reducing activity of Lactococcus lactisFEBS JOURNAL, Issue 10 2010D. Michelon Lactococcus lactis can decrease the redox potential at pH 7 (Eh7) from 200 to ,200 mV in oxygen free Man,Rogosa,Sharpe media. Neither the consumption of oxidizing compounds or the release of reducing compounds during lactic acid fermentation were involved in the decrease in Eh7 by the bacteria. Thiol groups located on the bacterial cell surface appear to be the main components that are able to establish a greater exchange current between the Pt electrode and the bacteria. After the final Eh7 (,200 mV) was reached, only thiol-reactive reagents could restore the initial Eh7 value. Inhibition of the proton motive force showed no effect on maintaining the final Eh7 value. These results suggest that maintaining the exofacial thiol (,SH) groups in a reduced state does not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wall-bound proteins and may participate in protecting cells against oxidative stress. [source] Death-associated protein kinase (DAPK) and signal transduction: blebbing in programmed cell deathFEBS JOURNAL, Issue 1 2010Miia Bovellan Death-associated protein kinase (DAPK) regulates many distinct signalling events, including apoptosis, autophagy and membrane blebbing. The role of DAPK in the blebbing process is only beginning to be understood and, in this review, we will first summarize what is known about the cytoskeletal proteins and signalling cascades that participate in bleb growth and retraction and then highlight how DAPK integrates with these processes. Membrane blebs are quasispherical cellular protrusions that have a lifetime of approximately 2 min. During expansion, blebs are initially devoid of actin, although actomyosin contractions provide the motive force for growth. Once growth slows, an actin cortex reforms and actin-bundling and contractile proteins are recruited. Finally, myosin contraction powers bleb retraction into the cell body. Blebbing occurs in a variety of cell types, from cancerous cells to embryonic cells, and can be seen in cellular phenomena as diverse as cell spreading, movement, cytokinesis and cell death. Although the machinery that executes this is still undefined in detail, the conservation of blebbing phenomenon suggests a fundamental role in metazoans and DAPK offers a door to further dissect this fascinating process. [source] Bio-inspired Photoelectric Conversion Based on Smart-Gating NanochannelsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Liping Wen Abstract Inspired by the light-driven, cross-membrane proton pump of biological systems, a photoelectric conversion system based on a smart-gating, proton-driven nanochannel is constructed. In this system, solar energy is the only source of cross-membrane proton motive force that induces a diffusion potential and photocurrent flowing through the external circuit. Although the obtained photoelectric conversion performance is lower than that of conventional solid photovoltaic devices, it is believed that higher efficiencies can be generated by enhancing the protonation capacity of the photo-acid molecules, optimizing the membrane, and synthesizing high-performance photosensitive molecules. This type of facile and environmentally friendly photoelectric conversion has potential applications for future energy demands such as the production of power for in vivo medical devices. [source] Bioenergetics of the formyl-methanofuran dehydrogenase and heterodisulfide reductase reactions in Methanothermobacter thermautotrophicusFEBS JOURNAL, Issue 1 2003Linda M. I. De Poorter The synthesis of formyl-methanofuran and the reduction of the heterodisulfide (CoM-S-S-CoB) of coenzyme M (HS-CoM) and coenzyme B (HS-CoB) are two crucial, H2 -dependent reactions in the energy metabolism of methanogenic archaea. The bioenergetics of the reactions in vivo were studied in chemostat cultures and in cell suspensions of Methanothermobacter thermautotrophicus metabolizing at defined dissolved hydrogen partial pressures (,pH2). Formyl-methanofuran synthesis is an endergonic reaction (,G°, = +16 kJ·mol,1). By analyzing the concentration ratios between formyl-methanofuran and methanofuran in the cells, free energy changes under experimental conditions (,G,) were found to range between +10 and +35 kJ·mol,1 depending on the pH2 applied. The comparison with the sodium motive force indicated that the reaction should be driven by the import of a variable number of two to four sodium ions. Heterodisulfide reduction (,G°, = ,40 kJ·mol,1) was associated with free energy changes as high as ,55 to ,80 kJ·mol,1. The values were determined by analyzing the concentrations of CoM-S-S-CoB, HS-CoM and HS-CoB in methane-forming cells operating under a variety of hydrogen partial pressures. Free energy changes were in equilibrium with the proton motive force to the extent that three to four protons could be translocated out of the cells per reaction. Remarkably, an apparent proton translocation stoichiometry of three held for cells that had been grown at pH2<0.12 bar, whilst the number was four for cells grown above that concentration. The shift occurred within a narrow pH2 span around 0.12 bar. The findings suggest that the methanogens regulate the bioenergetic machinery involved in CoM-S-S-CoB reduction and proton pumping in response to the environmental hydrogen concentrations. [source] The impact of metabolic state on Cd adsorption onto bacterial cellsGEOBIOLOGY, Issue 3 2007K. J. JOHNSON ABSTRACT This study examines the effect of bacterial metabolism on the adsorption of Cd onto Gram-positive and Gram-negative bacterial cells. Metabolically active Gram-positive cells adsorbed significantly less Cd than non-metabolizing cells. Gram-negative cells, however, showed no systematic difference in Cd adsorption between metabolizing and non-metabolizing cells. The effect of metabolism on Cd adsorption to Gram-positive cells was likely due to an influx of protons in and around the cell wall from the metabolic proton motive force, promoting competition between Cd and protons for adsorption sites on the cell wall. The relative lack of a metabolic effect on Cd adsorption onto Gram-negative compared to Gram-positive cells suggests that Cd binding in Gram-negative cells is focused in a region of the cell wall that is not reached, or is unaffected by this proton flux. Thermodynamic modeling was used to estimate that proton pumping causes the pH in the cell wall of metabolizing Gram-positive bacteria to decrease from the bulk solution value of 7.0 to approximately 5.7. [source] Critical contact residues that mediate polymerization of nematode major sperm proteinJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2008Antonio del Castillo-Olivares Abstract The polymerization of protein filaments provides the motive force in a variety of cellular processes involving cell motility and intracellular transport. Regulated assembly and disassembly of the major sperm protein (MSP) underlies amoeboid movement in nematode sperm, and offers an attractive model system for characterizing the biomechanical properties of filament formation and force generation. To that end, structure-function studies of MSP from the nematode Caenorhabditis elegans have been performed. Recombinant MSP was purified from Escherichia coli using a novel affinity chromatography technique, and filament assembly was assessed by in vitro polymerization in the presence of polyethylene glycol. Prior molecular studies and structure from X-ray crystallography have implicated specific residues in protein,protein interactions necessary for filament assembly. Purified MSP containing substitutions in these residues fails to form filaments in vitro. Short peptides based on predicted sites of interaction also effectively disrupt MSP polymerization. These results confirm the structural determination of intermolecular contacts and demonstrate the importance of these residues in MSP assembly. J. Cell. Biochem. 104: 477,487, 2008. © 2007 Wiley-Liss, Inc. [source] Prostate carcinoma cells selected by long-term exposure to reduced oxygen tension show remarkable biochemical plasticity via modulation of superoxide, HIF-1, levels, and energy metabolismJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2007Jeanne Bourdeau-Heller Cancer cells are able to tolerate levels of O2 that are damaging or lethal to normal cells; we hypothesize that this tolerance is the result of biochemical plasticity which maintains cellular homeostasis of both energy levels and oxidation state. In order to examine this hypothesis, we used different O2 levels as a selective agent during long-term culture of DU145 prostate cancer cells to develop three isogenic cell lines that grow in normoxic (4%), hyperoxic (21%), or hypoxic (1%) O2 conditions. Growth characteristics and O2 consumption differed significantly between these cell lines without changes in ATP levels or altered sensitivity to 2-deoxy- D -glucose, an inhibitor of glycolysis. O2 consumption was significantly higher in the hyperoxic line as was the level of endogenous superoxide. The hypoxic cell line regulated the chemical gradient of the proton motive force (PMF) independent of the electrical component without O2 -dependent changes in Hif-1, levels. In contrast, the normoxic line regulated Hif-1, without tight regulation of the chemical component of the PMF noted in the hypoxic cell line. From these studies, we conclude that selection of prostate cancer cells by long-term exposure to low ambient levels of O2 resulted in cells with unique biochemical properties in which energy metabolism, reactive oxygen species (ROS), and HIF-1, levels are modulated to allow cell survival and growth. Thus, cancer cells exhibit remarkable biochemical plasticity in response to various O2 levels. J. Cell. Physiol. 212:744,752, 2007. © 2007 Wiley-Liss, Inc. [source] Effect of the proton motive force inhibitor carbonyl cyanide- m -chlorophenylhydrazone (CCCP) on Pseudomonas aeruginosa biofilm developmentLETTERS IN APPLIED MICROBIOLOGY, Issue 4 2008A. Ikonomidis Abstract Aims:, Proton motive force (PMF) inhibition enhances the intracellular accumulation of autoinducers possibly interfering with biofilm formation. We evaluated the effect of the PMF inhibitor carbonyl cyanide- m -chlorophenylhydrazone (CCCP) on Pseudomonas aeruginosa biofilm development. Methods and Results:, Four epidemiologically unrelated P. aeruginosa isolates were studied. A MexAB-oprM overproducing strain was used as control. Expression of gene mexB was examined and biofilm formation after incubation with 0, 12·5 and 25 ,mol l,1 of CCCP was investigated. Mean values of optical density were analysed with one-way analysis of variance and t -test. Two isolates subexpressed mexB gene and only 25 ,mol l,1 of CCCP affected biofilm formation. Biofilms of the other two isolates and control strain PA140 exhibited significantly lower absorbance (P ranging from <0·01 to <0·05) with either 12·5 or 25 ,mol l,1 of CCCP. Conclusions:, The PMF inhibitor CCCP effect was correlated with the expression of MexAB-OprM efflux system and found to compromise biofilm formation in P. aeruginosa. Significance and Impact of the Study:, These data suggest that inhibition of PMF-dependent trasporters might decrease biofilm formation in P. aeruginosa. [source] Physical, functional and conditional interactions between ArcAB and phage shock proteins upon secretin-induced stress in Escherichia coliMOLECULAR MICROBIOLOGY, Issue 1 2009Goran Jovanovic Summary The phage shock protein (Psp) system found in enterobacteria is induced in response to impaired inner membrane integrity (where the Psp response is thought to help maintain the proton motive force of the cell) and is implicated in the virulence of pathogens such as Yersinia and Salmonella. We provided evidence that the two-component ArcAB system was involved in induction of the Psp response in Escherichia coli and now report that role of ArcAB is conditional. ArcAB, predominantly through the action of ArcA regulated genes, but also via a direct ArcB,Psp interaction, is required to propagate the protein IV (pIV)-dependent psp -inducing signal(s) during microaerobiosis, but not during aerobiosis or anaerobiosis. We show that ArcB directly interacts with the PspB, possibly by means of the PspB leucine zipper motif, thereby allowing cross-communication between the two systems. In addition we demonstrate that the pIV-dependent induction of psp expression in anaerobiosis is independent of PspBC, establishing that PspA and PspF can function as a minimal Psp system responsive to inner membrane stress. [source] FliL is essential for swarming: motor rotation in absence of FliL fractures the flagellar rod in swarmer cells of Salmonella entericaMOLECULAR MICROBIOLOGY, Issue 2 2008Ursula Attmannspacher Summary fliL is the first gene in a flagellar operon that specifies members of the switch complex and type III export system in Salmonella enterica and Escherichia coli, but no function has been ascribed to this gene thus far. Here we report that a fliL mutant is slightly impaired for swimming but completely defective in swarming in both organisms, and have studied this phenotype further in S. enterica. We have found that on swarm agar, mutant cells release or ,eject' their flagellar filaments. The released filaments are attached to the hook and part of the rod structure; we have identified the distal rod protein FlgG but not the proximal rod protein FlgF in these filaments. Rod fracture was not observed if flagellar rotation was prevented by removal of proteins that supply proton flow through the motor. Based on these and other results, we propose that motors experience a higher torque on swarm agar owing to an increased proton motive force, and that FliL allows the rod to withstand the increased torsional stress. The flagella-release phenotype of the S. enterica fliL mutant has a bearing on FliL-dependent flagellar ejection during the swimmer- to stalk-cell transition in the developmental cycle of Caulobacter crescentus. [source] Differentiation between electron transport sensing and proton motive force sensing by the Aer and Tsr receptors for aerotaxisMOLECULAR MICROBIOLOGY, Issue 3 2006Jessica C. Edwards Summary Aerotaxis (oxygen-seeking) behaviour in Escherichia coli is a response to changes in the electron transport system and not oxygen per se. Because changes in proton motive force (PMF) are coupled to respiratory electron transport, it is difficult to differentiate between PMF, electron transport or redox, all primary candidates for the signal sensed by the aerotaxis receptors, Aer and Tsr. We constructed electron transport mutants that produced different respiratory H+/e, stoichiometries. These strains expressed binary combinations of one NADH dehydrogenase and one quinol oxidase. We then introduced either an aer or tsr mutation into each mutant to create two sets of electron transport mutants. In vivo H+/e, ratios for strains grown in glycerol medium ranged from 1.46 ± 0.18,3.04 ± 0.47, but rates of respiration and growth were similar. The PMF jump in response to oxygen was proportional to the H+/e, ratio in each set of mutants (r2 = 0.986,0.996). The length of Tsr-mediated aerotaxis responses increased with the PMF jump (r2 = 0.988), but Aer-mediated responses did not correlate with either PMF changes (r2 = 0.297) or the rate of electron transport (r2 = 0.066). Aer-mediated responses were linked to NADH dehydrogenase I, although there was no absolute requirement. The data indicate that Tsr responds to changes in PMF, but strong Aer responses to oxygen are associated with redox changes in NADH dehydrogenase I. [source] Use of an in-house approach to study the three-dimensional structures of various outer membrane proteins: structure of the alcaligin outer membrane transporter FauA from Bordetella pertussisACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Karl Brillet Bordetella pertussis is the bacterial agent of whooping cough in humans. Under iron-limiting conditions, it produces the siderophore alcaligin. Released to the extracellular environment, alcaligin chelates iron, which is then taken up as a ferric alcaligin complex via the FauA outer membrane transporter. FauA belongs to a family of TonB-dependent outer membrane transporters that function using energy derived from the proton motive force. Using an in-house protocol for membrane-protein expression, purification and crystallization, FauA was crystallized in its apo form together with three other TonB-dependent transporters from different organisms. Here, the protocol used to study FauA is described and its three-dimensional structure determined at 2.3,Å resolution is discussed. [source] Crystallization and preliminary X-ray analysis of a C-terminal TonB fragment from Escherichia coliACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2004Jiri Koedding The TonB protein located in the cell wall of Gram-negative bacteria mediates the proton motive force from the cytoplasmic membrane to specific outer membrane transporters. A C-terminal fragment of TonB from Escherichia coli consisting of amino-acid residues 147,239 (TonB-92) has been purified and crystallized. Crystals grew in space group P21 to dimensions of about 1.0 × 0.12 × 0.12,mm. A native data set has been obtained to 1.09,Å resolution. [source] | |||||||||||||