Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
BBA - Biomembranes (v.1717, #2)
Alkaline pH homeostasis in bacteria: New insights by Etana Padan; Eitan Bibi; Masahiro Ito; Terry A. Krulwich (pp. 67-88).
The capacity of bacteria to survive and grow at alkaline pH values is of widespread importance in the epidemiology of pathogenic bacteria, in remediation and industrial settings, as well as in marine, plant-associated and extremely alkaline ecological niches. Alkali-tolerance and alkaliphily, in turn, strongly depend upon mechanisms for alkaline pH homeostasis, as shown in pH shift experiments and growth experiments in chemostats at different external pH values. Transcriptome and proteome analyses have recently complemented physiological and genetic studies, revealing numerous adaptations that contribute to alkaline pH homeostasis. These include elevated levels of transporters and enzymes that promote proton capture and retention (e.g., the ATP synthase and monovalent cation/proton antiporters), metabolic changes that lead to increased acid production, and changes in the cell surface layers that contribute to cytoplasmic proton retention. Targeted studies over the past decade have followed up the long-recognized importance of monovalent cations in active pH homeostasis. These studies show the centrality of monovalent cation/proton antiporters in this process while microbial genomics provides information about the constellation of such antiporters in individual strains. A comprehensive phylogenetic analysis of both eukaryotic and prokaryotic genome databases has identified orthologs from bacteria to humans that allow better understanding of the specific functions and physiological roles of the antiporters. Detailed information about the properties of multiple antiporters in individual strains is starting to explain how specific monovalent cation/proton antiporters play dominant roles in alkaline pH homeostasis in cells that have several additional antiporters catalyzing ostensibly similar reactions. New insights into the pH-dependent Na+/H+ antiporter NhaA that plays an important role in Escherichia coli have recently emerged from the determination of the structure of NhaA. This review highlights the approaches, major findings and unresolved problems in alkaline pH homeostasis, focusing on the small number of well-characterized alkali-tolerant and extremely alkaliphilic bacteria.
Keywords: Abbreviations; ΔpH; transmembrane pH gradient; ΔΨ; transmembrane electrical gradient; AIB; α-aminoisobutyric acid; BCECF; 2′,7′-; bis; -(2-carboxyethyl)-5(and-6)-carboxyfluorescein; LB; Luria–Bertani medium; PMF; proton-motive force, a transmembrane electrochemical gradient of protons composed of the ΔpH (alkaline inside) and ΔΨ (negative inside); SCWP; secondary cell wall polymers; SMF; sodium-motive force; Tc; tetracycline; TMAO; trimethylamine; N; -oxide; TMS; trans membrane segment; MDR; multi-drug transporter; CPA; cation proton antiporters; Ec; Escherichia coli; Vc; Vibrio cholerae; Mj; Methanococcus jannaschii; Bs; Bacillus subtilis; Bh; Bacillus halodurans; C-125; Bp; Bacillus pseudofirmus; OF4; Sa; Staphylococcus aureuspH homeostasis; Na; +; (K; +; )/H; +; antiporters; Alkaline pH homeostasis; NhaA; Mrp; MdfA; Tet(L)
Alkaline pH homeostasis in bacteria: New insights by Etana Padan; Eitan Bibi; Masahiro Ito; Terry A. Krulwich (pp. 67-88).
The capacity of bacteria to survive and grow at alkaline pH values is of widespread importance in the epidemiology of pathogenic bacteria, in remediation and industrial settings, as well as in marine, plant-associated and extremely alkaline ecological niches. Alkali-tolerance and alkaliphily, in turn, strongly depend upon mechanisms for alkaline pH homeostasis, as shown in pH shift experiments and growth experiments in chemostats at different external pH values. Transcriptome and proteome analyses have recently complemented physiological and genetic studies, revealing numerous adaptations that contribute to alkaline pH homeostasis. These include elevated levels of transporters and enzymes that promote proton capture and retention (e.g., the ATP synthase and monovalent cation/proton antiporters), metabolic changes that lead to increased acid production, and changes in the cell surface layers that contribute to cytoplasmic proton retention. Targeted studies over the past decade have followed up the long-recognized importance of monovalent cations in active pH homeostasis. These studies show the centrality of monovalent cation/proton antiporters in this process while microbial genomics provides information about the constellation of such antiporters in individual strains. A comprehensive phylogenetic analysis of both eukaryotic and prokaryotic genome databases has identified orthologs from bacteria to humans that allow better understanding of the specific functions and physiological roles of the antiporters. Detailed information about the properties of multiple antiporters in individual strains is starting to explain how specific monovalent cation/proton antiporters play dominant roles in alkaline pH homeostasis in cells that have several additional antiporters catalyzing ostensibly similar reactions. New insights into the pH-dependent Na+/H+ antiporter NhaA that plays an important role in Escherichia coli have recently emerged from the determination of the structure of NhaA. This review highlights the approaches, major findings and unresolved problems in alkaline pH homeostasis, focusing on the small number of well-characterized alkali-tolerant and extremely alkaliphilic bacteria.
Keywords: Abbreviations; ΔpH; transmembrane pH gradient; ΔΨ; transmembrane electrical gradient; AIB; α-aminoisobutyric acid; BCECF; 2′,7′-; bis; -(2-carboxyethyl)-5(and-6)-carboxyfluorescein; LB; Luria–Bertani medium; PMF; proton-motive force, a transmembrane electrochemical gradient of protons composed of the ΔpH (alkaline inside) and ΔΨ (negative inside); SCWP; secondary cell wall polymers; SMF; sodium-motive force; Tc; tetracycline; TMAO; trimethylamine; N; -oxide; TMS; trans membrane segment; MDR; multi-drug transporter; CPA; cation proton antiporters; Ec; Escherichia coli; Vc; Vibrio cholerae; Mj; Methanococcus jannaschii; Bs; Bacillus subtilis; Bh; Bacillus halodurans; C-125; Bp; Bacillus pseudofirmus; OF4; Sa; Staphylococcus aureuspH homeostasis; Na; +; (K; +; )/H; +; antiporters; Alkaline pH homeostasis; NhaA; Mrp; MdfA; Tet(L)
Proteolipid of vacuolar H+-ATPase of Plasmodium falciparum: cDNA cloning, gene organization and complementation of a yeast null mutant by Shouki Yatsushiro; Shinya Taniguchi; Toshihide Mitamura; Hiroshi Omote; Yoshinori Moriyama (pp. 89-96).
Vacuolar H+-ATPase (V-ATPase), an electrogenic proton pump, is highly expressed in Plasmodium falciparum, the human malaria parasite. Although V-ATPase-driven proton transport is involved in various physiological processes in the parasite, the overall features of the V-ATPase of P. falciparum, including the gene organization and biogenesis, are far less known. Here, we report cDNA cloning of proteolipid subunit c of P. falciparum, the smallest and most highly hydrophobic subunit of V-ATPase. RT-PCR analysis as well as Northern blotting indicated expression of the proteolipid gene in the parasite cells. cDNA, which encodes a complete reading frame comprising 165 amino acids, was obtained, and its deduced amino acid sequence exhibits 52 and 57% similarity to the yeast and human counterparts, respectively. Southern blot analysis suggested the presence of a single copy of the proteolipid gene, with 5 exons and 4 introns. Upon transfection of the cDNA into a yeast null mutant, the cells became able to grow at neutral pH, accompanied by vesicular accumulation of quinacrine. In contrast, a mutated proteolipid with replacement of glutamate residue 138 with glutamine did not lead to recovery of the growth ability or vesicular accumulation of quinacrine. These results indicated that the cDNA actually encodes the proteolipid of P. falciparum and that the proteolipid is functional in yeast.
Keywords: Abbreviations; RT-PCR; reserve transcriptional polymerase chain reaction; V-ATPase; vacuolar H; +; -ATPaseV-ATPase; Proteolipid; Subunit; c; Malaria; Plasmodium falciparum; Complementation; Yeast null mutant
Proteolipid of vacuolar H+-ATPase of Plasmodium falciparum: cDNA cloning, gene organization and complementation of a yeast null mutant by Shouki Yatsushiro; Shinya Taniguchi; Toshihide Mitamura; Hiroshi Omote; Yoshinori Moriyama (pp. 89-96).
Vacuolar H+-ATPase (V-ATPase), an electrogenic proton pump, is highly expressed in Plasmodium falciparum, the human malaria parasite. Although V-ATPase-driven proton transport is involved in various physiological processes in the parasite, the overall features of the V-ATPase of P. falciparum, including the gene organization and biogenesis, are far less known. Here, we report cDNA cloning of proteolipid subunit c of P. falciparum, the smallest and most highly hydrophobic subunit of V-ATPase. RT-PCR analysis as well as Northern blotting indicated expression of the proteolipid gene in the parasite cells. cDNA, which encodes a complete reading frame comprising 165 amino acids, was obtained, and its deduced amino acid sequence exhibits 52 and 57% similarity to the yeast and human counterparts, respectively. Southern blot analysis suggested the presence of a single copy of the proteolipid gene, with 5 exons and 4 introns. Upon transfection of the cDNA into a yeast null mutant, the cells became able to grow at neutral pH, accompanied by vesicular accumulation of quinacrine. In contrast, a mutated proteolipid with replacement of glutamate residue 138 with glutamine did not lead to recovery of the growth ability or vesicular accumulation of quinacrine. These results indicated that the cDNA actually encodes the proteolipid of P. falciparum and that the proteolipid is functional in yeast.
Keywords: Abbreviations; RT-PCR; reserve transcriptional polymerase chain reaction; V-ATPase; vacuolar H; +; -ATPaseV-ATPase; Proteolipid; Subunit; c; Malaria; Plasmodium falciparum; Complementation; Yeast null mutant
Voltage gating and anions, especially phosphate: A model system by Padmanava Pradhan; Ranajeet Ghose; Michael E. Green (pp. 97-103).
The voltage sensor of voltage gated sodium and potassium channels consists of four sets of transmembrane segments, of which one, called S4, contains at least four arginines; these are presumed to each carry positive charges. The channel opening is usually attributed to the outward (i.e., toward the extracellular side of the membrane) motion of S4. The evidence for this motion is based on certain experiments that appear to show differential access to parts of S4 from the intracellular and extracellular sides of the membrane in the open and closed states. A newly available structure [S.B. Long, E.B. Campbell and R. MacKinnon, Crystal structure of a mammalian voltage-dependent Shaker family K+ channel. Science 309 (2005) 897–903; S.B. Long, E.B. Campbell, R. MacKinnon, Voltage sensor of Kv1.2: structural basis of electromechanical coupling. Science 309 (2005) 903–908][1,2] has now been used to argue for a large scale motion, although, as a static structure, it is not conclusive. In this paper, we consider the effect of anions in the surrounding medium. Phosphate is present in the intracellular as well as the extracellular fluid, apparently at hundreds of micromolar concentration, or more. There is evidence in the literature suggesting that phosphate–arginine complexes are rather strong. In a recent calculation one of us [M.E. Green, A possible role for phosphate in complexing the arginines of S4 in voltage gated channels J. Theor. Biol. 233 (2005) 337–341][3] has shown that a model peptide with a 2:1 arg:phosphate complex should have a favorable geometry. Here, we present NMR evidence of the existence of phosphate complexes of a model peptide with two arginines separated by two hydrophobic residues, the same spacing as in S4 segments. The complexes (there are different complexes for HPO42− and for H2PO4− [3]) form with concentrations of peptide in the range of hundreds of micromolar, making it significant in the biological context. NMR spectra provide changes in chemical shift as functions of both phosphate concentration and pH. The resulting curves show titration of the phosphate, with its standard pK. Possible implications for other anion–S4 interactions, including ion pairs rather than complexes, as with Cl−, are also discussed.
Keywords: Voltage gating; Ion channel; S4; Anion; Phosphate; Arginine complex
Voltage gating and anions, especially phosphate: A model system by Padmanava Pradhan; Ranajeet Ghose; Michael E. Green (pp. 97-103).
The voltage sensor of voltage gated sodium and potassium channels consists of four sets of transmembrane segments, of which one, called S4, contains at least four arginines; these are presumed to each carry positive charges. The channel opening is usually attributed to the outward (i.e., toward the extracellular side of the membrane) motion of S4. The evidence for this motion is based on certain experiments that appear to show differential access to parts of S4 from the intracellular and extracellular sides of the membrane in the open and closed states. A newly available structure [S.B. Long, E.B. Campbell and R. MacKinnon, Crystal structure of a mammalian voltage-dependent Shaker family K+ channel. Science 309 (2005) 897–903; S.B. Long, E.B. Campbell, R. MacKinnon, Voltage sensor of Kv1.2: structural basis of electromechanical coupling. Science 309 (2005) 903–908][1,2] has now been used to argue for a large scale motion, although, as a static structure, it is not conclusive. In this paper, we consider the effect of anions in the surrounding medium. Phosphate is present in the intracellular as well as the extracellular fluid, apparently at hundreds of micromolar concentration, or more. There is evidence in the literature suggesting that phosphate–arginine complexes are rather strong. In a recent calculation one of us [M.E. Green, A possible role for phosphate in complexing the arginines of S4 in voltage gated channels J. Theor. Biol. 233 (2005) 337–341][3] has shown that a model peptide with a 2:1 arg:phosphate complex should have a favorable geometry. Here, we present NMR evidence of the existence of phosphate complexes of a model peptide with two arginines separated by two hydrophobic residues, the same spacing as in S4 segments. The complexes (there are different complexes for HPO42− and for H2PO4− [3]) form with concentrations of peptide in the range of hundreds of micromolar, making it significant in the biological context. NMR spectra provide changes in chemical shift as functions of both phosphate concentration and pH. The resulting curves show titration of the phosphate, with its standard pK. Possible implications for other anion–S4 interactions, including ion pairs rather than complexes, as with Cl−, are also discussed.
Keywords: Voltage gating; Ion channel; S4; Anion; Phosphate; Arginine complex
Effect of salt concentration on membrane lysis pressure by Catherine C. Logisz; Jennifer S. Hovis (pp. 104-108).
Cell membranes are capable of withstanding significant osmotic stress, the exact amount of which varies with the lipid composition. In this paper, we examine the effect that salt concentration has on the lysis pressure of membranes containing anionic lipids. Vesicles containing varying amounts of phosphatidylcholine and phosphatidylglycerol were osmotically stressed using NaCl as the osmolyte. The lysis pressure was observed to vary linearly with the Debye screening length and the extent of the variation was linear with anionic lipid content. The implications these results have for cells that frequently encounter low solute environments are discussed.
Keywords: Anionic lipid; Lysis pressure; Osmotic pressure; Membrane stability
Effect of salt concentration on membrane lysis pressure by Catherine C. Logisz; Jennifer S. Hovis (pp. 104-108).
Cell membranes are capable of withstanding significant osmotic stress, the exact amount of which varies with the lipid composition. In this paper, we examine the effect that salt concentration has on the lysis pressure of membranes containing anionic lipids. Vesicles containing varying amounts of phosphatidylcholine and phosphatidylglycerol were osmotically stressed using NaCl as the osmolyte. The lysis pressure was observed to vary linearly with the Debye screening length and the extent of the variation was linear with anionic lipid content. The implications these results have for cells that frequently encounter low solute environments are discussed.
Keywords: Anionic lipid; Lysis pressure; Osmotic pressure; Membrane stability
Sodium-dependent glucose transporter reduces peroxynitrite and cell injury caused by cisplatin in renal tubular epithelial cells by Akira Ikari; Yoshiaki Nagatani; Mitsutoshi Tsukimoto; Hitoshi Harada; Masao Miwa; Kuniaki Takagi (pp. 109-117).
Cisplatin causes nephropathy accompanied by two types of cell death, necrosis and apoptosis, according to its dosage. The mechanisms of necrosis are still unclear. In this study, we examined how high doses of cisplatin induce cell injury and whether a high affinity sodium-dependent glucose transporter (SGLT1) has a cytoprotective function in renal epithelial LLC-PK1 cells. Cisplatin decreased in transepithelial electrical resistance (TER) and increased in the number of necrotic dead cells in a time dependent manner. Phloridzin, a potent SGLT1 inhibitor, enhanced both TER decrease and increase of necrotic dead cells caused by cisplatin. Cisplatin increased in the intracellular nitric oxide, superoxide anion and peroxynitrite productions. Phloridzin enhanced the peroxynitrite production caused by cisplatin. The intracellular diffusion of ZO-1 and TER decrease caused by cisplatin were inhibited by N-nitro-l-arginine methyl ester, a nitric oxide synthase inhibitor. Protein kinase C was not involved in the cisplatin-induced injury. 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato iron (III) and reduced glutathione, peroxynitrite scavengers, inhibited the cisplatin-induced ZO-1 diffusion, TER decrease, and increase of necrotic dead cells. These results suggest that peroxynitrite is a key mediator in the nephrotoxicity caused by high doses of cisplatin. SGLT1 endogenously carries out the cytoprotective function by the reduction of peroxynitrite production.
Keywords: Abbreviations; AMG; Methyl α-glucopyranoside; eNOS; endothelial nitric oxide synthase; FeTPPS; 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato iron (III); GSH; reduced glutathione; l; -NAME; N; -nitro-; l; -arginine methyl ester; OCTs; organic cation transporters; PI; propidium iodide; PKC; protein kinase C; PMA; phorbol 12-myristate 13-acetate; RNS; reactive nitrogen species; ROS; reactive oxygen species; TER; transepithelial electrical resistance; TJ; tight junction; ZO; zonula occludensCisplatin; Cytoprotection; Peroxynitrite; Sodium-dependent glucose transporter; Tight junction; ZO-1
Sodium-dependent glucose transporter reduces peroxynitrite and cell injury caused by cisplatin in renal tubular epithelial cells by Akira Ikari; Yoshiaki Nagatani; Mitsutoshi Tsukimoto; Hitoshi Harada; Masao Miwa; Kuniaki Takagi (pp. 109-117).
Cisplatin causes nephropathy accompanied by two types of cell death, necrosis and apoptosis, according to its dosage. The mechanisms of necrosis are still unclear. In this study, we examined how high doses of cisplatin induce cell injury and whether a high affinity sodium-dependent glucose transporter (SGLT1) has a cytoprotective function in renal epithelial LLC-PK1 cells. Cisplatin decreased in transepithelial electrical resistance (TER) and increased in the number of necrotic dead cells in a time dependent manner. Phloridzin, a potent SGLT1 inhibitor, enhanced both TER decrease and increase of necrotic dead cells caused by cisplatin. Cisplatin increased in the intracellular nitric oxide, superoxide anion and peroxynitrite productions. Phloridzin enhanced the peroxynitrite production caused by cisplatin. The intracellular diffusion of ZO-1 and TER decrease caused by cisplatin were inhibited by N-nitro-l-arginine methyl ester, a nitric oxide synthase inhibitor. Protein kinase C was not involved in the cisplatin-induced injury. 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato iron (III) and reduced glutathione, peroxynitrite scavengers, inhibited the cisplatin-induced ZO-1 diffusion, TER decrease, and increase of necrotic dead cells. These results suggest that peroxynitrite is a key mediator in the nephrotoxicity caused by high doses of cisplatin. SGLT1 endogenously carries out the cytoprotective function by the reduction of peroxynitrite production.
Keywords: Abbreviations; AMG; Methyl α-glucopyranoside; eNOS; endothelial nitric oxide synthase; FeTPPS; 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato iron (III); GSH; reduced glutathione; l; -NAME; N; -nitro-; l; -arginine methyl ester; OCTs; organic cation transporters; PI; propidium iodide; PKC; protein kinase C; PMA; phorbol 12-myristate 13-acetate; RNS; reactive nitrogen species; ROS; reactive oxygen species; TER; transepithelial electrical resistance; TJ; tight junction; ZO; zonula occludensCisplatin; Cytoprotection; Peroxynitrite; Sodium-dependent glucose transporter; Tight junction; ZO-1
Combined cold, acid, ethanol shocks in Oenococcus oeni: Effects on membrane fluidity and cell viability by Son Chu-Ky; Raphaëlle Tourdot-Marechal; Pierre-André Marechal; Jean Guzzo (pp. 118-124).
The effects of combined cold, acid and ethanol on the membrane physical state and on the survival of Oenococcus oeni were investigated. Membrane fluidity was monitored on intact whole O. oeni cells subjected to single and combined cold, acid and ethanol shocks by using fluorescence anisotropy with 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. Results showed that cold shocks (14 and 8 °C) strongly rigidified plasma membrane but did not affect cell survival. In contrast, ethanol shocks (10–14% v/v) induced instantaneous membrane fluidisation followed by rigidification and resulted in low viability. Acid shocks (pH 4.0 and pH 3.0) exerted a rigidifying effect on membrane without affecting cell viability. Whatever the shock orders, combined cold (14 °C) and ethanol (14% v/v) shocks resulted in strong membrane rigidification. Interestingly, O. oeni survived combined cold and ethanol shocks more efficiently than single ethanol shock. Membrane rigidification was induced by ethanol-and-acid (10% v/v - pH 3.5) shock and correlated with total cell death. In contrast, O. oeni recovered its viability when subjected to cold (8 °C)-then-ethanol-and-acid shock which strongly rigidified the membrane. Our results suggested a positive short-term effect of combined cold, acid and ethanol shocks on membrane fluidity and viability of O. oeni.
Keywords: Combined shock; Membrane fluidity; Cell viability; Oenococcus oeni
Combined cold, acid, ethanol shocks in Oenococcus oeni: Effects on membrane fluidity and cell viability by Son Chu-Ky; Raphaëlle Tourdot-Marechal; Pierre-André Marechal; Jean Guzzo (pp. 118-124).
The effects of combined cold, acid and ethanol on the membrane physical state and on the survival of Oenococcus oeni were investigated. Membrane fluidity was monitored on intact whole O. oeni cells subjected to single and combined cold, acid and ethanol shocks by using fluorescence anisotropy with 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. Results showed that cold shocks (14 and 8 °C) strongly rigidified plasma membrane but did not affect cell survival. In contrast, ethanol shocks (10–14% v/v) induced instantaneous membrane fluidisation followed by rigidification and resulted in low viability. Acid shocks (pH 4.0 and pH 3.0) exerted a rigidifying effect on membrane without affecting cell viability. Whatever the shock orders, combined cold (14 °C) and ethanol (14% v/v) shocks resulted in strong membrane rigidification. Interestingly, O. oeni survived combined cold and ethanol shocks more efficiently than single ethanol shock. Membrane rigidification was induced by ethanol-and-acid (10% v/v - pH 3.5) shock and correlated with total cell death. In contrast, O. oeni recovered its viability when subjected to cold (8 °C)-then-ethanol-and-acid shock which strongly rigidified the membrane. Our results suggested a positive short-term effect of combined cold, acid and ethanol shocks on membrane fluidity and viability of O. oeni.
Keywords: Combined shock; Membrane fluidity; Cell viability; Oenococcus oeni