1
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Li J, Li Y, Koide A, Kuang H, Torres VJ, Koide S, Wang DN, Traaseth NJ. Proton-coupled transport mechanism of the efflux pump NorA. Nat Commun 2024; 15:4494. [PMID: 38802368 PMCID: PMC11130294 DOI: 10.1038/s41467-024-48759-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 05/13/2024] [Indexed: 05/29/2024] Open
Abstract
Efflux pump antiporters confer drug resistance to bacteria by coupling proton import with the expulsion of antibiotics from the cytoplasm. Despite efforts there remains a lack of understanding as to how acid/base chemistry drives drug efflux. Here, we uncover the proton-coupling mechanism of the Staphylococcus aureus efflux pump NorA by elucidating structures in various protonation states of two essential acidic residues using cryo-EM. Protonation of Glu222 and Asp307 within the C-terminal domain stabilized the inward-occluded conformation by forming hydrogen bonds between the acidic residues and a single helix within the N-terminal domain responsible for occluding the substrate binding pocket. Remarkably, deprotonation of both Glu222 and Asp307 is needed to release interdomain tethering interactions, leading to opening of the pocket for antibiotic entry. Hence, the two acidic residues serve as a "belt and suspenders" protection mechanism to prevent simultaneous binding of protons and drug that enforce NorA coupling stoichiometry and confer antibiotic resistance.
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Affiliation(s)
- Jianping Li
- Department of Chemistry, New York University, New York, NY, USA
| | - Yan Li
- Department of Cell Biology, New York University School of Medicine, New York, NY, USA
| | - Akiko Koide
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY, USA
- Department of Medicine, New York University School of Medicine, New York, NY, USA
| | - Huihui Kuang
- Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY, USA
| | - Victor J Torres
- Department of Microbiology, New York University School of Medicine, New York, NY, USA
- Antimicrobial-Resistant Pathogens Program, New York University School of Medicine, New York, NY, USA
| | - Shohei Koide
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY, USA
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | - Da-Neng Wang
- Department of Cell Biology, New York University School of Medicine, New York, NY, USA.
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2
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Li Y, Ge X. Molecular Dynamics Investigation of MFS Efflux Pump MdfA Reveals an Intermediate State between Its Inward and Outward Conformations. Int J Mol Sci 2022; 24:ijms24010356. [PMID: 36613823 PMCID: PMC9820426 DOI: 10.3390/ijms24010356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Revised: 12/22/2022] [Accepted: 12/23/2022] [Indexed: 12/28/2022] Open
Abstract
Multidrug resistance poses a major challenge to antibiotic therapy. A principal cause of antibiotic resistance is through active export by efflux pumps embedded in the bacterial membrane. Major facilitator superfamily (MFS) efflux pumps constitute a major group of transporters, which are often related to quinolone resistance in clinical settings. Although a rocker-switch model is proposed for description of their conformational transitions, detailed changes in this process remain poorly understood. Here we used MdfA from E. coli as a representative MFS efflux pump to investigate factors that can affect its conformational transition in silico. Molecular dynamics (MD) simulations of MdfA's inward and outward conformations revealed an intermediate state between these two conformations. By comparison of the subtle differences between the intermediate state and the average state, we indicated that conformational transition from outward to inward was initiated by protonation of the periplasmic side. Subsequently, hydrophilic interaction of the periplasmic side with water was promoted and the regional structure of helix 1 was altered to favor this process. As the hydrophobic interaction between MdfA and membrane was also increased, energy was concentrated and stored for the opposite transition. In parallel, salt bridges at the cytoplasmic side were altered to lower probabilities to facilitate the entrance of substrate. In summary, we described the total and local changes during MdfA's conformational transition, providing insights for the development of potential inhibitors.
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Affiliation(s)
| | - Xizhen Ge
- Correspondence: ; Tel.: +86-10-5207-2337
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3
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Stautz J, Hellmich Y, Fuss MF, Silberberg JM, Devlin JR, Stockbridge RB, Hänelt I. Molecular Mechanisms for Bacterial Potassium Homeostasis. J Mol Biol 2021; 433:166968. [PMID: 33798529 DOI: 10.1016/j.jmb.2021.166968] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 03/11/2021] [Accepted: 03/22/2021] [Indexed: 10/21/2022]
Abstract
Potassium ion homeostasis is essential for bacterial survival, playing roles in osmoregulation, pH homeostasis, regulation of protein synthesis, enzyme activation, membrane potential adjustment and electrical signaling. To accomplish such diverse physiological tasks, it is not surprising that a single bacterium typically encodes several potassium uptake and release systems. To understand the role each individual protein fulfills and how these proteins work in concert, it is important to identify the molecular details of their function. One needs to understand whether the systems transport ions actively or passively, and what mechanisms or ligands lead to the activation or inactivation of individual systems. Combining mechanistic information with knowledge about the physiology under different stress situations, such as osmostress, pH stress or nutrient limitation, one can identify the task of each system and deduce how they are coordinated with each other. By reviewing the general principles of bacterial membrane physiology and describing the molecular architecture and function of several bacterial K+-transporting systems, we aim to provide a framework for microbiologists studying bacterial potassium homeostasis and the many K+-translocating systems that are still poorly understood.
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Affiliation(s)
- Janina Stautz
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Yvonne Hellmich
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Michael F Fuss
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Jakob M Silberberg
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Jason R Devlin
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States
| | - Randy B Stockbridge
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States.
| | - Inga Hänelt
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany.
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4
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Abstract
Bacterial cytoplasmic membrane vesicles provide a unique experimental system for studying active transport. Vesicles are prepared by lysis of osmotically sensitized cells (i.e., protoplasts or spheroplasts) and comprise osmotically intact, unit-membrane-bound sacs that are approximately 0.5-1.0 μm in diameter and devoid of internal structure. Their metabolic activities are restricted to those provided by the enzymes of the membrane itself, and each vesicle is functional. The energy source for accumulation of a particular substrate can be determined by studying which compounds or experimental conditions drive solute accumulation, and metabolic conversion of the transported substrate or the energy source is minimal. These properties of the vesicle system constitute a considerable advantage over intact cells, as the system provides clear definition of the reactions involved in the transport process. This discussion is not intended as a general review but is concerned with respiration-dependent active transport in membrane vesicles from Escherichia coli. Emphasis is placed on experimental observations demonstrating that respiratory energy is converted primarily into work in the form of a solute concentration gradient that is driven by a proton electrochemical gradient, as postulated by the chemiosmotic theory of Peter Mitchell.
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Affiliation(s)
- H R Kaback
- Department of Physiology and Department of Microbiology, Immunology and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, California, 90095, USA
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5
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Seica AFS, Iancu CV, Pfeilschifter B, Madej MG, Choe JY, Hellwig P. Asp 22 drives the protonation state of the Staphylococcus epidermidis glucose/H + symporter. J Biol Chem 2020; 295:15253-15261. [PMID: 32859752 DOI: 10.1074/jbc.ra120.014069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 08/26/2020] [Indexed: 12/24/2022] Open
Abstract
The Staphylococcus epidermidis glucose/H+ symporter (GlcPSe) is a membrane transporter highly specific for glucose and a homolog of the human glucose transporters (GLUT, SLC2 family). Most GLUTs and their bacterial counterparts differ in the transport mechanism, adopting uniport and sugar/H+ symport, respectively. Unlike other bacterial GLUT homologs (for example, XylE), GlcPSe has a loose H+/sugar coupling. Asp22 is part of the proton-binding site of GlcPSe and crucial for the glucose/H+ co-transport mechanism. To determine how pH variations affect the proton site and the transporter, we performed surface-enhanced IR absorption spectroscopy on the immobilized GlcPSe We found that Asp22 has a pKa of 8.5 ± 0.1, a value consistent with that determined previously for glucose transport, confirming the central role of this residue for the transport mechanism of GlcPSe A neutral replacement of the negatively charged Asp22 led to positive charge displacements over the entire pH range, suggesting that the polarity change of the WT reflects the protonation state of Asp22 We expected that the substitution of the residue Ile105 for a serine, located within hydrogen-bonding distance to Asp22, would change the microenvironment, but the pKa of Asp22 corresponded to that of the WT. A167E mutation, selected in analogy to the XylE, introduced an additional protonatable site and perturbed the protonation state of Asp22, with the latter now exhibiting a pKa of 6.4. These studies confirm that Asp22 is the proton-binding residue in GlcPSe and show that charged residues in its vicinity affect the pKa of glucose/H+ symport.
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Affiliation(s)
- Ana Filipa Santos Seica
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France
| | - Cristina V Iancu
- Department of Chemistry, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, North Carolina, USA
| | - Benedikt Pfeilschifter
- University of Regensburg, Institute of Biophysics and Physical Biochemistry, Regensburg, Germany
| | - M Gregor Madej
- University of Regensburg, Institute of Biophysics and Physical Biochemistry, Regensburg, Germany
| | - Jun-Yong Choe
- Department of Chemistry, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, North Carolina, USA; Department of Biochemistry and Molecular Biology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA.
| | - Petra Hellwig
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France
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6
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Reyes-Fernández EZ, Schuldiner S. Acidification of Cytoplasm in Escherichia coli Provides a Strategy to Cope with Stress and Facilitates Development of Antibiotic Resistance. Sci Rep 2020; 10:9954. [PMID: 32561799 PMCID: PMC7305162 DOI: 10.1038/s41598-020-66890-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Accepted: 05/27/2020] [Indexed: 01/21/2023] Open
Abstract
Awareness of the problem of antimicrobial resistance (AMR) has escalated, and drug-resistant infections are named among the most urgent issues facing clinicians today. Bacteria can acquire resistance to antibiotics by a variety of mechanisms that, at times, involve changes in their metabolic status, thus altering diverse biochemical reactions, many of them pH-dependent. In this work, we found that modulation of the cytoplasmic pH (pHi) of Escherichia coli provides a thus far unexplored strategy to support resistance. We show here that the acidification of the cytoplasmic pH is a previously unrecognized consequence of the activation of the marRAB operon. The acidification itself contributes to the full implementation of the resistance phenotype. We measured the pHi of two resistant strains, developed in our laboratory, that carry mutations in marR that activate the marRAB operon. The pHi of both strains is lower than that of the wild type strain. Inactivation of the marRAB response in both strains weakens resistance, and pHi increases back to wild type levels. Likewise, we showed that exposure of wild type cells to weak acids that caused acidification of the cytoplasm induced a resistant phenotype, independent of the marRAB response. We speculate that the decrease of the cytoplasmic pH brought about by activation of the marRAB response provides a signaling mechanism that modifies metabolic pathways and serves to cope with stress and to lower metabolic costs.
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Affiliation(s)
- Esmeralda Z Reyes-Fernández
- Department Biological Chemistry, Institute of Life Sciences, Silberman Bldg. 1-339, Edmond J. Safra Campus, Hebrew University of Jerusalem, Givat Ram, Jerusalem, 91904, Israel
| | - Shimon Schuldiner
- Department Biological Chemistry, Institute of Life Sciences, Silberman Bldg. 1-339, Edmond J. Safra Campus, Hebrew University of Jerusalem, Givat Ram, Jerusalem, 91904, Israel.
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7
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The proton electrochemical gradient induces a kinetic asymmetry in the symport cycle of LacY. Proc Natl Acad Sci U S A 2019; 117:977-981. [PMID: 31889006 PMCID: PMC6969543 DOI: 10.1073/pnas.1916563117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protonation and deprotonation of Glu325 with a pKa of 10.5 is required for symport. Moreover, the H+ electrochemical gradient (∆μ∼H+) accelerates deprotonation on the intracellular side with a 50- to 100-fold decrease in the Km. To probe the pK on the cytoplasmic side of the membrane, rates of lactose/H+ efflux were determined from pH 5.0 to 9.0 without or with a membrane potential (ΔΨ, interior positive) in right-side-out membrane vesicles. WT lactose efflux has an apparent pK of ∼7.2 that is unaffected by ΔΨ, mutant E325A is defective, and pH or ΔΨ (interior positive) has no effect. The effect of ΔΨ (interior positive) on the Km for efflux with WT LacY is insignificant relative to the marked effect on influx. LacY catalyzes accumulation of galactosides against a concentration gradient by coupling galactoside and H+ transport (i.e., symport). While alternating access of sugar- and H+-binding sites to either side of the membrane is driven by binding and dissociation of sugar, the electrochemical H+ gradient (∆μ∼H+) functions kinetically by decreasing the Km for influx 50- to 100-fold with no change in Kd. The affinity of protonated LacY for sugar has an apparent pK (pKapp) of ∼10.5, due specifically to the pKa of Glu325, a residue that plays an irreplaceable role in coupling. In this study, rates of lactose/H+ efflux were measured from pH 5.0 to 9.0 in the absence or presence of a membrane potential (ΔΨ, interior positive), and the effect of the imposed ΔΨ on the kinetics of efflux was also studied in right-side-out membrane vesicles. The findings reveal that ∆μ∼H+ induces an asymmetry in the transport cycle based on the following observations: 1) the efflux rate of WT LacY exhibits a pKapp of ∼7.2 that is unaffected by the imposed ΔΨ; 2) ΔΨ increases the rate of efflux at all tested pH values, but enhancement is almost 2 orders of magnitude less than observed for influx; 3) mutant Glu325 ˗ Ala does little or no efflux in the absence or presence of ΔΨ, and ambient pH has no effect; and 4) the effect of ΔΨ (interior positive) on the Km for efflux is almost insignificant relative to the 50- to 100-fold decrease in the Km for influx driven by ΔΨ (interior negative).
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8
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Kaback HR, Guan L. It takes two to tango: The dance of the permease. J Gen Physiol 2019; 151:878-886. [PMID: 31147449 PMCID: PMC6605686 DOI: 10.1085/jgp.201912377] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 05/14/2019] [Indexed: 11/20/2022] Open
Abstract
The lactose permease (LacY) of Escherichia coli is the prototype of the major facilitator superfamily, one of the largest families of membrane transport proteins. Structurally, two pseudo-symmetrical six-helix bundles surround a large internal aqueous cavity. Single binding sites for galactoside and H+ are positioned at the approximate center of LacY halfway through the membrane at the apex of the internal cavity. These features enable LacY to function by an alternating-access mechanism that can catalyze galactoside/H+ symport in either direction across the cytoplasmic membrane. The H+-binding site is fully protonated under physiological conditions, and subsequent sugar binding causes transition of the ternary complex to an occluded intermediate that can open to either side of the membrane. We review the structural and functional evidence that has provided new insight into the mechanism by which LacY achieves active transport against a concentration gradient.
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Affiliation(s)
- H Ronald Kaback
- Department of Physiology and Department of Microbiology, Immunology and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA
| | - Lan Guan
- Department of Cell Physiology and Molecular Biophysics, Center of Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
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9
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Abstract
Lactose permease is a paradigm for the major facilitator superfamily, the largest family of ion-coupled membrane transport proteins known at present. LacY carries out the coupled stoichiometric symport of a galactoside with an H+, using the free energy released from downhill translocation of H+ to drive accumulation of galactosides against a concentration gradient. In neutrophilic Escherichia coli, internal pH is kept at ∼7.6 over the physiological range, but the apparent pK (pKapp) for galactoside binding is 10.5. Surface-enhanced infrared absorption spectroscopy (SEIRAS) demonstrates that the high pKa is due to Glu325 (helix X), which must be protonated for LacY to bind galactoside effectively. Deprotonation is also obligatory for turnover, however. Here, we utilize SEIRAS to study the effect of mutating residues in the immediate vicinity of Glu325 on its pKa The results are consistent with the idea that Arg302 (helix IX) is important for deprotonation of Glu325.
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10
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Knyazev DG, Kuttner R, Zimmermann M, Sobakinskaya E, Pohl P. Driving Forces of Translocation Through Bacterial Translocon SecYEG. J Membr Biol 2018; 251:329-343. [PMID: 29330604 PMCID: PMC6028853 DOI: 10.1007/s00232-017-0012-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2017] [Accepted: 12/22/2017] [Indexed: 11/09/2022]
Abstract
This review focusses on the energetics of protein translocation via the Sec translocation machinery. First we complement structural data about SecYEG's conformational rearrangements by insight obtained from functional assays. These include measurements of SecYEG permeability that allow assessment of channel gating by ligand binding and membrane voltage. Second we will discuss the power stroke and Brownian ratcheting models of substrate translocation and the role that the two models assign to the putative driving forces: (i) ATP (SecA) and GTP (ribosome) hydrolysis, (ii) interaction with accessory proteins, (iii) membrane partitioning and folding, (iv) proton motive force (PMF), and (v) entropic contributions. Our analysis underlines how important energized membranes are for unravelling the translocation mechanism in future experiments.
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Affiliation(s)
- Denis G Knyazev
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria.
| | - Roland Kuttner
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria
| | - Mirjam Zimmermann
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria
| | | | - Peter Pohl
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria
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11
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Eguchi Y, Fukumori Y, Taoka A. Measuring magnetosomal pH of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using pH-sensitive fluorescent proteins. Biosci Biotechnol Biochem 2018; 82:1243-1251. [PMID: 29557302 DOI: 10.1080/09168451.2018.1451739] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Magnetotactic bacteria synthesize uniform-sized and regularly shaped magnetic nanoparticles in their organelles termed magnetosomes. Homeostasis of the magnetosome lumen must be maintained for its role accomplishment. Here, we developed a method to estimate the pH of a single living cell of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using a pH-sensitive fluorescent protein E2GFP. Using the pH measurement, we estimated that the cytoplasmic pH was approximately 7.6 and periplasmic pH was approximately 7.2. Moreover, we estimated pH in the magnetosome lumen and cytoplasmic surface using fusion proteins of E2GFP and magnetosome-associated proteins. The pH in the magnetosome lumen increased during the exponential growth phase when magnetotactic bacteria actively synthesize magnetite crystals, whereas pH at the magnetosome surface was not affected by the growth stage. This live-cell pH measurement method will help for understanding magnetosome pH homeostasis to reveal molecular mechanisms of magnetite biomineralization in the bacterial organelle.
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Affiliation(s)
- Yukako Eguchi
- a Department of Life Science, Graduate School of Natural Science and Technology , Kanazawa University , Kanazawa , Japan
| | - Yoshihiro Fukumori
- b Faculty of Natural System, Institute of Science and Engineering , Kanazawa University , Kanazawa , Japan
| | - Azuma Taoka
- b Faculty of Natural System, Institute of Science and Engineering , Kanazawa University , Kanazawa , Japan.,c Bio-AFM Frontier Research Center, College of Science and Engineering , Kanazawa University , Kanazawa , Japan
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12
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Wray R, Iscla I, Gao Y, Li H, Wang J, Blount P. Dihydrostreptomycin Directly Binds to, Modulates, and Passes through the MscL Channel Pore. PLoS Biol 2016; 14:e1002473. [PMID: 27280286 PMCID: PMC4900634 DOI: 10.1371/journal.pbio.1002473] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 05/04/2016] [Indexed: 12/23/2022] Open
Abstract
The primary mechanism of action of the antibiotic dihydrostreptomycin is binding to and modifying the function of the bacterial ribosome, thus leading to decreased and aberrant translation of proteins; however, the routes by which it enters the bacterial cell are largely unknown. The mechanosensitive channel of large conductance, MscL, is found in the vast majority of bacterial species, where it serves as an emergency release valve rescuing the cell from sudden decreases in external osmolarity. While it is known that MscL expression increases the potency of dihydrostreptomycin, it has remained unclear if this effect is due to a direct interaction. Here, we use a combination of genetic screening, MD simulations, and biochemical and mutational approaches to determine if dihydrostreptomycin directly interacts with MscL. Our data strongly suggest that dihydrostreptomycin binds to a specific site on MscL and modifies its conformation, thus allowing the passage of K+ and glutamate out of, and dihydrostreptomycin into, the cell.
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Affiliation(s)
- Robin Wray
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Irene Iscla
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Ya Gao
- School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Hua Li
- School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang, China
| | - Junmei Wang
- Green Center for Systems Biology and Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Paul Blount
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
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13
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Albert LS, Brown DG. Variation in bacterial ATP concentration during rapid changes in extracellular pH and implications for the activity of attached bacteria. Colloids Surf B Biointerfaces 2015; 132:111-6. [PMID: 26037699 DOI: 10.1016/j.colsurfb.2015.05.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Revised: 05/07/2015] [Accepted: 05/12/2015] [Indexed: 11/28/2022]
Abstract
In this study we investigated the relationship between a rapid change in extracellular pH and the alteration of bacterial ATP concentration. This relationship is a key component of a hypothesis indicating that bacterial bioenergetics - the creation of ATP from ADP via a proton gradient across the cytoplasmic membrane - can be altered by the physiochemical charge-regulation effect, which results in a pH shift at the bacteria's surface upon adhesion to another surface. The bacterial ATP concentration was measured during a rapid change in extracellular pH from a baseline pH of 7.2 to pH values between 3.5 and 10.5. Experiments were conducted with four neutrophilic bacterial strains, including the Gram-negative Escherichia coli and Pseudomonas putida and the Gram-positive Bacillus subtilis and Staphylococcus epidermidis. A change in bulk pH produced an immediate response in bacterial ATP, demonstrating a direct link between changes in extracellular pH and cellular bioenergetics. In general, the shifts in ATP were similar across the four bacterial strains, with results following an exponential relationship between the extracellular pH and cellular ATP concentration. One exception occurred with S. epidermidis, where there was no variation in cellular ATP at acidic pH values, and this finding is consistent with this species' ability to thrive under acidic conditions. These results provide insight into obtaining a desired bioenergetic response in bacteria through (i) the application of chemical treatments to vary the local pH and (ii) the selection and design of surfaces resulting in local pH modification of attached bacteria via the charge-regulation effect.
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Affiliation(s)
- Lynal S Albert
- Department of Civil & Environmental Engineering, Lehigh University, Bethlehem, PA 18015, United States
| | - Derick G Brown
- Department of Civil & Environmental Engineering, Lehigh University, Bethlehem, PA 18015, United States.
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14
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Biocompatible click chemistry enabled compartment-specific pH measurement inside E. coli. Nat Commun 2014; 5:4981. [PMID: 25236616 PMCID: PMC4174402 DOI: 10.1038/ncomms5981] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2014] [Accepted: 08/13/2014] [Indexed: 11/15/2022] Open
Abstract
Bioorthogonal reactions, especially the Cu(I)-catalyzed azide-alkyne cycloaddition, have revolutionized our ability to label and manipulate biomolecules under living conditions. The cytotoxicity of Cu(I) ions, however, has hindered the application of this reaction in the internal space of living cells. By systematically surveying a panel of Cu(I)-stabilizing ligands in promoting protein labeling within the cytoplasm of E. coli, here we identify a highly efficient and biocompatible catalyst for intracellular modification of proteins by azide-alkyne cycloaddition. This reaction permits us to conjugate an environment-sensitive fluorophore site-specifically onto HdeA, an acid-stress chaperone that adopts pH-dependent conformational changes, in both the periplasm and cytoplasm of E. coli. The resulting protein-fluorophore hybrid pH indicators enable compartment-specific pH measurement to determine the pH gradient across the E. coli cytoplasmic membrane. This construct also allows the measurement of E. coli transmembrane potential, and the determination of the proton motive force across its inner membrane under normal and acid-stress conditions.
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15
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Export of a single drug molecule in two transport cycles by a multidrug efflux pump. Nat Commun 2014; 5:4615. [DOI: 10.1038/ncomms5615] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Accepted: 07/07/2014] [Indexed: 11/08/2022] Open
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16
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Structure of the YajR transporter suggests a transport mechanism based on the conserved motif A. Proc Natl Acad Sci U S A 2013; 110:14664-9. [PMID: 23950222 DOI: 10.1073/pnas.1308127110] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The major facilitator superfamily (MFS) is the largest family of secondary active transporters and is present in all life kingdoms. Detailed structural basis of the substrate transport and energy-coupling mechanisms of these proteins remain to be elucidated. YajR is a putative proton-driven MFS transporter found in many Gram-negative bacteria. Here we report the crystal structure of Escherichia coli YajR at 3.15 Å resolution in an outward-facing conformation. In addition to having the 12 canonical transmembrane helices, the YajR structure includes a unique 65-residue C-terminal domain which is independently stable. The structure is unique in illustrating the functional role of "sequence motif A." This highly conserved element is seen to stabilize the outward conformation of YajR and suggests a general mechanism for the conformational change between the inward and outward states of the MFS transporters.
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17
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Mottaleb SA, Rodríguez-Navarro A, Haro R. Knockouts of Physcomitrella patens CHX1 and CHX2 Transporters Reveal High Complexity of Potassium Homeostasis. ACTA ACUST UNITED AC 2013; 54:1455-68. [DOI: 10.1093/pcp/pct096] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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18
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Gopal R, Seo CH, Song PI, Park Y. Effect of repetitive lysine-tryptophan motifs on the bactericidal activity of antimicrobial peptides. Amino Acids 2012; 44:645-60. [PMID: 22914980 PMCID: PMC3549253 DOI: 10.1007/s00726-012-1388-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Accepted: 08/07/2012] [Indexed: 12/19/2022]
Abstract
Previous studies identified lysine- and tryptophan-rich sequences within various cationic antimicrobial peptides. In the present study, we synthesized a series of peptides composed of lysine (K)-tryptophan (W) repeats (KW)n (where n equals 2, 3, 4 or 5) with amidation of the C-terminal to increase cationicity. We found that increases in chain length up to (KW)4 enhanced the peptides’ antibacterial activity; (KW)5 exhibited somewhat less bactericidal activity than (KW)4. Cytotoxicity, measured as lysis of human red blood cells, also increased with increasing chain length. With (KW)5, reduced antibacterial activity and increased cytotoxicity correlated with greater hydrophobicity and self-aggregation in the aqueous environment. The peptides acted by inducing rapid collapse of the bacterial transmembrane potential and induction of membrane permeability. The mode of interaction of the peptides and the phosphate groups of lipopolysaccharide was dependent upon the peptides’ ability to permeate the membrane. Longer peptides [(KW)4 and (KW)5] but not shorter peptides [(KW)2 and (KW)3] strongly bound and partially inserted into negatively charged, anionic lipid bilayers. These longer peptides also induced membrane permeabilization and aggregation of lipid vesicles. The peptides had a disordered structure in aqueous solution, and only (KW)4 and (KW)5 displayed a folded conformation on lipid membranes. Moreover, (KW)4 destroyed and agglutinated bacterial cells, demonstrating its potential as an antimicrobial agent. Collectively, the results show (KW)4 to be the most efficacious peptide in the (KW)n series, exhibiting strong antibacterial activity with little cytotoxicity.
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Affiliation(s)
- Ramamourthy Gopal
- Research Center for Proteineous Materials, Chosun University, Kwangju, South Korea
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19
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Stoffels L, Krehenbrink M, Berks BC, Unden G. Thiosulfate reduction in Salmonella enterica is driven by the proton motive force. J Bacteriol 2012; 194:475-85. [PMID: 22081391 PMCID: PMC3256639 DOI: 10.1128/jb.06014-11] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2011] [Accepted: 11/01/2011] [Indexed: 11/20/2022] Open
Abstract
Thiosulfate respiration in Salmonella enterica serovar Typhimurium is catalyzed by the membrane-bound enzyme thiosulfate reductase. Experiments with quinone biosynthesis mutants show that menaquinol is the sole electron donor to thiosulfate reductase. However, the reduction of thiosulfate by menaquinol is highly endergonic under standard conditions (ΔE°' = -328 mV). Thiosulfate reductase activity was found to depend on the proton motive force (PMF) across the cytoplasmic membrane. A structural model for thiosulfate reductase suggests that the PMF drives endergonic electron flow within the enzyme by a reverse loop mechanism. Thiosulfate reductase was able to catalyze the combined oxidation of sulfide and sulfite to thiosulfate in a reverse of the physiological reaction. In contrast to the forward reaction the exergonic thiosulfate-forming reaction was PMF independent. Electron transfer from formate to thiosulfate in whole cells occurs predominantly by intraspecies hydrogen transfer.
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Affiliation(s)
- Laura Stoffels
- Institute for Microbiology and Wine Research, Johannes Gutenberg-University of Mainz, Mainz, Germany
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Martin Krehenbrink
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Ben C. Berks
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Gottfried Unden
- Institute for Microbiology and Wine Research, Johannes Gutenberg-University of Mainz, Mainz, Germany
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20
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Abstract
Diverse mechanisms for pH sensing and cytoplasmic pH homeostasis enable most bacteria to tolerate or grow at external pH values that are outside the cytoplasmic pH range they must maintain for growth. The most extreme cases are exemplified by the extremophiles that inhabit environments with a pH of below 3 or above 11. Here, we describe how recent insights into the structure and function of key molecules and their regulators reveal novel strategies of bacterial pH homeostasis. These insights may help us to target certain pathogens more accurately and to harness the capacities of environmental bacteria more efficiently.
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Affiliation(s)
- Terry A. Krulwich
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, Box 1603, 1 Gustave L. Levy Place, New York, NY 10029, USA; Tel. 212-241-7280; Fax. 212-996-7214
| | - George Sachs
- Departments of Physiology and Medicine, David Geffen School of Medicine at UCLA, 405 Hilgard Ave., Los Angeles, California 90024, USA Tel. 310-268-3923, Fax 310-312-9478
| | - Etana Padan
- Alexander Silberman Institute of Life Sciences, Hebrew University, Jerusalem 91904, Israel, Tel. 972 2 6585094, Fax 972 2 658947
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21
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The regulatory C-terminal domain of subunit ε of F₀F₁ ATP synthase is dispensable for growth and survival of Escherichia coli. J Bacteriol 2011; 193:2046-52. [PMID: 21335453 DOI: 10.1128/jb.01422-10] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The C-terminal domain of subunit ε of the bacterial F₀F₁ ATP synthase is reported to be an intrinsic inhibitor of ATP synthesis/hydrolysis activity in vitro, preventing wasteful hydrolysis of ATP under low-energy conditions. Mutants defective in this regulatory domain exhibited no significant difference in growth rate, molar growth yield, membrane potential, or intracellular ATP concentration under a wide range of growth conditions and stressors compared to wild-type cells, suggesting this inhibitory domain is dispensable for growth and survival of Escherichia coli.
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22
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Delmer DP, Benziman M, Padan E. Requirement for a membrane potential for cellulose synthesis in intact cells of Acetobacter xylinum. Proc Natl Acad Sci U S A 2010; 79:5282-6. [PMID: 16593224 PMCID: PMC346880 DOI: 10.1073/pnas.79.17.5282] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The marked lability in cell-free preparations of the enzyme system involved in cellulose biosynthesis in most organisms studied led us to investigate factors responsible for loss of activity on cellular disruption. Previous studies have led to the suggestion that the existence of a transmembrane electrical potential (DeltaPsi) may be one factor responsible for maintaining an active system in intact cells. In this report, we show that dissipation of the DeltaPsi in metabolizing cells of Acetobacter xylinum results in severe inhibition of cellulose synthesis. The effect can be reversed by restoration of the DeltaPsi. Inhibition of cellulose biosynthesis by dissipation of the DeltaPsi can be observed under conditions in which no substantial impairment of energy metabolism occurs-i.e., under conditions in which a transmembrane pH gradient is of sufficient magnitude to maintain an adequate overall protonmotive force across the membrane. The inhibition of cellulose biosynthesis is specifically related to changes in the DeltaPsi, since the process can proceed normally in the absence of the pH gradient. These results support the suggestion that loss of the DeltaPsi on cellular disruption may be one of the factors responsible for the low capacity for cellulose synthesis in isolated membrane preparations and also raise the possibility that modulation of the DeltaPsi could be one means of regulating the rate of cellulose synthesis in vivo.
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Affiliation(s)
- D P Delmer
- Michigan State University-Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
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23
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Huang Y, Huang J, Chen Y. Alpha-helical cationic antimicrobial peptides: relationships of structure and function. Protein Cell 2010; 1:143-52. [PMID: 21203984 DOI: 10.1007/s13238-010-0004-3] [Citation(s) in RCA: 340] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2009] [Accepted: 10/29/2009] [Indexed: 12/27/2022] Open
Abstract
Antimicrobial peptides (AMPs), with their extraordinary properties, such as broad-spectrum activity, rapid action and difficult development of resistance, have become promising molecules as new antibiotics. Despite their various mechanisms of action, the interaction of AMPs with the bacterial cell membrane is the key step for their mode of action. Moreover, it is generally accepted that the membrane is the primary target of most AMPs, and the interaction between AMPs and eukaryotic cell membranes (causing toxicity to host cells) limits their clinical application. Therefore, researchers are engaged in reforming or de novo designing AMPs as a 'single-edged sword' that contains high antimicrobial activity yet low cytotoxicity against eukaryotic cells. To improve the antimicrobial activity of AMPs, the relationship between the structure and function of AMPs has been rigorously pursued. In this review, we focus on the current knowledge of α-helical cationic antimicrobial peptides, one of the most common types of AMPs in nature.
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Affiliation(s)
- Yibing Huang
- Key Laboratory for Molecular Enzymology and Engineering of Ministry of Education, Jilin University, Changchun 130021, China
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24
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Smirnova I, Kasho V, Sugihara J, Choe JY, Kaback HR. Residues in the H+ translocation site define the pKa for sugar binding to LacY. Biochemistry 2009; 48:8852-60. [PMID: 19689129 DOI: 10.1021/bi9011918] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A remarkably high pKa of approximately 10.5 has been determined for sugar-binding affinity to the lactose permease of Escherichia coli (LacY), indicating that, under physiological conditions, substrate binds to fully protonated LacY. We have now systematically tested site-directed replacements for the residues involved in sugar binding, as well as H+ translocation and coupling, in order to determine which residues may be responsible for this alkaline pKa. Mutations in the sugar-binding site (Glu126, Trp151, Glu269) markedly decrease affinity for sugar but do not alter the pKa for binding. In contrast, replacements for residues involved in H+ translocation (Arg302, Tyr236, His322, Asp240, Glu325, Lys319) exhibit pKa values for sugar binding that are either shifted toward neutral pH or independent of pH. Values for the apparent dissociation constant for sugar binding (K(d)(app)) increase greatly for all mutants except neutral replacements for Glu325 or Lys319, which are characterized by remarkably high affinity sugar binding (i.e., low K(d)(app)) from pH 5.5 to pH 11. The pH dependence of the on- and off-rate constants for sugar binding measured directly by stopped-flow fluorometry implicates k(off) as a major factor for the affinity change at alkaline pH and confirms the effects of pH on K(d)(app) inferred from steady-state fluorometry. These results indicate that the high pKa for sugar binding by wild-type LacY cannot be ascribed to any single amino acid residue but appears to reside within a complex of residues involved in H+ translocation. There is structural evidence for water bound in this complex, and the water could be the site of protonation responsible for the pH dependence of sugar binding.
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Affiliation(s)
- Irina Smirnova
- Department of Physiology, University of California Los Angeles, Los Angeles, California 90095-7327, USA
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25
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Vooturi SK, Cheung CM, Rybak MJ, Firestine SM. Design, Synthesis, and Structure−Activity Relationships of Benzophenone-Based Tetraamides as Novel Antibacterial Agents. J Med Chem 2009; 52:5020-31. [DOI: 10.1021/jm900519b] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sunil K. Vooturi
- Department of Pharmaceutical Sciences
- Anti-Infective Research Laboratory
- Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, Michigan 48201
| | - Chrissy M. Cheung
- Department of Pharmaceutical Sciences
- Anti-Infective Research Laboratory
- Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, Michigan 48201
| | - Michael J. Rybak
- Department of Pharmaceutical Sciences
- Anti-Infective Research Laboratory
- Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, Michigan 48201
| | - Steven M. Firestine
- Department of Pharmaceutical Sciences
- Anti-Infective Research Laboratory
- Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, Michigan 48201
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26
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Chen Y, Guarnieri MT, Vasil AI, Vasil ML, Mant CT, Hodges RS. Role of peptide hydrophobicity in the mechanism of action of alpha-helical antimicrobial peptides. Antimicrob Agents Chemother 2006; 51:1398-406. [PMID: 17158938 PMCID: PMC1855469 DOI: 10.1128/aac.00925-06] [Citation(s) in RCA: 523] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the present study, the 26-residue amphipathic alpha-helical antimicrobial peptide V13KL (Y. Chen et al., J. Biol. Chem. 2005, 280:12316-12329, 2005) was used as the framework to study the effects of peptide hydrophobicity on the mechanism of action of antimicrobial peptides. Hydrophobicity was systematically decreased or increased by replacing leucine residues with less hydrophobic alanine residues or replacing alanine residues with more hydrophobic leucine residues on the nonpolar face of the helix, respectively. Hydrophobicity of the nonpolar face of the amphipathic helix was demonstrated to correlate with peptide helicity (measured by circular dichroism spectroscopy) and self-associating ability (measured by reversed-phase high-performance liquid chromatography temperature profiling) in aqueous environments. Higher hydrophobicity was correlated with stronger hemolytic activity. In contrast, there was an optimum hydrophobicity window in which high antimicrobial activity could be obtained. Decreased or increased hydrophobicity beyond this window dramatically decreased antimicrobial activity. The decreased antimicrobial activity at high peptide hydrophobicity can be explained by the strong peptide self-association which prevents the peptide from passing through the cell wall in prokaryotic cells, whereas increased peptide self-association had no effect on peptide access to eukaryotic membranes.
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Affiliation(s)
- Yuxin Chen
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Biomolecular Structure MS 8101, P.O. Box 6511, Aurora, CO 80045, USA
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27
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Chen Y, Vasil AI, Rehaume L, Mant CT, Burns JL, Vasil ML, Hancock REW, Hodges RS. Comparison of biophysical and biologic properties of alpha-helical enantiomeric antimicrobial peptides. Chem Biol Drug Des 2006; 67:162-73. [PMID: 16492164 PMCID: PMC3252236 DOI: 10.1111/j.1747-0285.2006.00349.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In our previous study (Chen et al. J Biol Chem 2005, 280:12316-12329), we utilized an alpha-helical antimicrobial peptide V(681) as the framework to study the effects of peptide hydrophobicity, amphipathicity, and helicity on biologic activities where we obtained several V(681) analogs with dramatic improvement in peptide therapeutic indices against gram-negative and gram-positive bacteria. In the present study, the D-enantiomers of three peptides--V(681), V13A(D) and V13K(L) were synthesized to compare biophysical and biologic properties with their enantiomeric isomers. Each D-enantiomer was shown by circular dichroism spectroscopy to be a mirror image of the corresponding L-isomer in benign conditions and in the presence of 50% trifluoroethanol. L- and D-enantiomers exhibited equivalent antimicrobial activities against a diverse group of Pseudomonas aeruginosa clinical isolates, various gram-negative and gram-positive bacteria and a fungus. In addition, L- and D-enantiomeric peptides were equally active in their ability to lyse human red blood cells. The similar activity of L- and D-enantiomeric peptides on prokaryotic or eukaryotic cell membranes suggests that there are no chiral receptors and the cell membrane is the sole target for these peptides. Peptide D-V13K(D) showed significant improvements in the therapeutic indices compared with the parent peptide V(681) by 53-fold against P. aeruginosa strains, 80-fold against gram-negative bacteria, 69-fold against gram-positive bacteria, and 33-fold against Candida albicans. The excellent stability of D-enantiomers to trypsin digestion (no proteolysis by trypsin) compared with the rapid breakdown of the L-enantiomers highlights the advantage of the D-enantiomers and their potential as clinical therapeutics.
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Affiliation(s)
- Yuxin Chen
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Biomolecular Structure MS 8101, PO Box 6511, Aurora, CO 80045, USA
| | - Adriana I. Vasil
- Department of Microbiology, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
| | - Linda Rehaume
- Department of Microbiology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Colin T. Mant
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Biomolecular Structure MS 8101, PO Box 6511, Aurora, CO 80045, USA
| | - Jane L. Burns
- Infectious Diseases Section, Children's Hospital and Regional Medical Center, University of Washington, Seattle, WA 98109, USA
| | - Michael L. Vasil
- Department of Microbiology, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
| | - Robert E. W. Hancock
- Department of Microbiology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Robert S. Hodges
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Biomolecular Structure MS 8101, PO Box 6511, Aurora, CO 80045, USA
- Corresponding author: Robert S. Hodges,
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28
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Abstract
Antimicrobial peptides (AMPs) of innate origin are agents of the most ancient form of defense systems. They can be found in a wide variety of species ranging from bacteria through insects to humans. Through the course of evolution, host organisms developed arsenals of AMPs that protect them against a large variety of invading pathogens including both Gram-negative and Gram-positive bacteria. At a time of increasing bacterial resistance, AMPs have been the focus of investigation in a number of laboratories worldwide. Although recent studies show that some of the peptides are likely to have intracellular targets, the vast majority of AMPs appear to act by permeabilization of the bacterial cell membrane. Their activity and selectivity are governed by the physicochemical parameters of the peptide chains as well as the properties of the membrane system itself. In this review, we will summarize some of the recent developments that provide us with a better understanding of the mode of action of this unique family of antibacterial agents. Particular attention will be given to the determinants of AMP-lipid bilayer interactions as well as to the different pore formation mechanisms. The emphasis will be on linear AMPs but representatives of cysteine-bridged AMPs will also be discussed.
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Affiliation(s)
- Orsolya Toke
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.
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29
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Rotem D, Schuldiner S. EmrE, a Multidrug Transporter from Escherichia coli, Transports Monovalent and Divalent Substrates with the Same Stoichiometry. J Biol Chem 2004; 279:48787-93. [PMID: 15371426 DOI: 10.1074/jbc.m408187200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Multidrug transporters recognize and transport substrates with apparently little common structural features. At times these substrates are neutral, negatively, or positively charged, and only limited information is available as to how these proteins deal with the energetic consequences of transport of substrates with different charges. Multidrug transporters and drug-specific efflux systems are responsible for clinically significant resistance to chemotherapeutic agents in pathogenic bacteria, fungi, parasites, and human cancer cells. Understanding how these efflux systems handle different substrates may also have practical implications in the development of strategies to overcome the resistance mechanisms mediated by these proteins. Here, we compare transport of monovalent and divalent substrates by EmrE, a multidrug transporter from Escherichia coli, in intact cells and in proteoliposomes reconstituted with the purified protein. The results demonstrated that whereas the transport of monovalent substrates involves charge movement (i.e. electrogenic), the transport of divalent substrate does not (i.e. electroneutral). Together with previous results, these findings suggest that an EmrE dimer exchanges two protons per substrate molecule during each transport cycle. In intact cells, under conditions where the only driving force is the electrical potential, EmrE confers resistance to monovalent substrates but not to divalent ones. In the presence of proton gradients, resistance to both types of substrates is detected. The finding that under some conditions EmrE does not remove certain types of drugs points out the importance of an in-depth understanding of mechanisms of action of multidrug transporters to devise strategies for coping with the problem of multidrug resistance.
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Affiliation(s)
- Dvir Rotem
- Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
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30
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Lewinson O, Adler J, Poelarends GJ, Mazurkiewicz P, Driessen AJM, Bibi E. The Escherichia coli multidrug transporter MdfA catalyzes both electrogenic and electroneutral transport reactions. Proc Natl Acad Sci U S A 2003; 100:1667-72. [PMID: 12578981 PMCID: PMC149890 DOI: 10.1073/pnas.0435544100] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The resistance of cells to many drugs simultaneously (multidrug resistance) often involves the expression of membrane transporters (Mdrs); each recognizes and expels a broad spectrum of chemically unrelated drugs from the cell. The Escherichia coli Mdr transporter MdfA is able to transport differentially charged substrates in exchange for protons. This includes neutral compounds, namely chloramphenicol and thiamphenicol, and lipophilic cations such as tetraphenylphosphonium and ethidium. Here we show that the chloramphenicol and thiamphenicol transport reactions are electrogenic, whereas the transport of several monovalent cationic substrates is electroneutral. Therefore, unlike with positively charged substrates, the transmembrane electrical potential (negative inside) constitutes a major part of the driving force for the transport of electroneutral substrates by MdfA. These results demonstrate an unprecedented ability of a single secondary transporter to catalyze discrete transport reactions that differ in their electrogenicity and are governed by different components of the proton motive force.
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Affiliation(s)
- Oded Lewinson
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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31
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Stingl K, Altendorf K, Bakker EP. Acid survival of Helicobacter pylori: how does urease activity trigger cytoplasmic pH homeostasis? Trends Microbiol 2002; 10:70-4. [PMID: 11827807 DOI: 10.1016/s0966-842x(01)02287-9] [Citation(s) in RCA: 125] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Helicobacter pylori can survive for several hours at pH 1 in the presence of urea. Under these conditions, the organism maintains its cytoplasmic pH at a value close to neutral. The role of the cytoplasmically located urease enzyme in this process is a matter of debate. We propose that cytoplasmic ammonia generated by the action of urease is protonated by H(+) ions leaking in from the acidic medium and that the NH(4)(+) formed is extruded from the cytoplasm via an as-yet-unidentified transport system. This mechanism is compared with the general mechanism of cytoplasmic pH homeostasis in microorganisms.
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Affiliation(s)
- Kerstin Stingl
- Abteilung Mikrobiologie, Universität Osnabrück, D-49069, Germany.
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32
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Riondet C, Cachon R, Waché Y, Alcaraz G, Diviès C. Changes in the proton-motive force in Escherichia coli in response to external oxidoreduction potential. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 262:595-9. [PMID: 10336647 DOI: 10.1046/j.1432-1327.1999.00429.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The pH homeostasis and proton-motive force (Deltap) of Escherichia coli are dependent on the surrounding oxidoreduction potential (ORP). Only the internal pH value and, thus, the membrane pH gradient (DeltapH) component of the Deltap is modified, while the membrane potential (DeltaPsi) does not change in a significant way. Under reducing conditions (Eh < 50 mV at pH 7.0), E. coli decreases its Deltap especially in acidic media (21% decrease at pH 7.0 and 48% at pH 5.0 for a 850-mV ORP decrease). Measurements of ATPase activity and membrane proton conductance (CH+m) depending on ORP and pH have shown that the internal pH decrease is due to an increase in membrane proton permeability without any modification of ATPase activity. We propose that low ORP values de-energize E. coli by modifying the thiol : disulfide balance of proteins, which leads to an increase in the membrane permeability to protons.
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Affiliation(s)
- C Riondet
- Laboratoire de Microbiologie U.A. INRA, ENSBANA, Université de Bourgogne, Dijon, France
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33
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Schuster S, Ouhabi R, Rigoulet M, Mazat JP. Modelling the interrelation between the transmembrane potential and pH difference across membranes with electrogenic proton transport upon build-up of the proton-motive force. ACTA ACUST UNITED AC 1998. [DOI: 10.1016/s0302-4598(98)00092-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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34
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Letellier L, Howard SP, Buckley JT. Studies on the energetics of proaerolysin secretion across the outer membrane of Aeromonas species. Evidence for a requirement for both the protonmotive force and ATP. J Biol Chem 1997; 272:11109-13. [PMID: 9111006 DOI: 10.1074/jbc.272.17.11109] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Aeromonas spp. secrete the channel-forming protein proaerolysin across their inner and outer membranes in separate steps using the general secretion pathway. Here we show that treating A. hydrophila or A. salmonicida with the protonophore carbonyl cyanide m-chorophenyl hydrazone blocks the second step in transport, secretion across the outer membrane from the periplasm, under conditions where the ATP levels in the cell are no different than the levels in control, secreting cells. A threshold for DeltaPsi was observed in the region of 120 mV, below which secretion by both species was inhibited. Treatment of cells with arsenate, which lowered ATP levels but did not affect DeltaPsi, also reduced secretion from the periplasm, an indication that there is an ATP requirement for this step independent of the requirement for DeltaPsi. Secretion across the outer membrane was also arrested by increasing the osmotic pressure of the medium, even though cellular ATP levels and DeltaPsi were not affected. This may be due to disruption of some necessary association between the inner and outer membranes.
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Affiliation(s)
- L Letellier
- Laboratoire des Biomembranes, URA CNRS 1116, Université Paris-Sud, Bâtiment 432, F-91405 Orsay, France
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35
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Chapter 22 Bacterial Na+/H+ antiporters — Molecular biology, biochemistry and physiology. HANDBOOK OF BIOLOGICAL PHYSICS 1996. [DOI: 10.1016/s1383-8121(96)80063-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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36
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Matsuzaki K, Sugishita K, Fujii N, Miyajima K. Molecular basis for membrane selectivity of an antimicrobial peptide, magainin 2. Biochemistry 1995; 34:3423-9. [PMID: 7533538 DOI: 10.1021/bi00010a034] [Citation(s) in RCA: 330] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Magainin peptides, isolated from Xenopus skin, kill bacteria by permeabilizing their cell membranes whereas they do not lyse erythrocytes. To elucidate the rationale for this membrane selectivity, we compared the effects of the membrane lipid composition and the transmembrane potential on the membrane-lytic power of magainin 2 with that of hemolytic melittin. The activity of magainin to zwitterionic phospholipids constituting the erythrocyte surface was extremely weak compared with that of melittin, and acidic phospholipids are necessary for effective action. The presence of sterols reduced the susceptibility of the membrane to magainin. The generation of an inside-negative transmembrane potential enhanced magainin-induced hemolysis. We can conclude that the absence of any acidic phospholipids on the outer monolayer and the abundant presence of cholesterol, combined with the lack of the transmembrane potential, contribute to the protection of erythrocytes from magainin's attack.
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Affiliation(s)
- K Matsuzaki
- Faculty of Pharmaceutical Sciences, Kyoto University, Japan
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37
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Pinner E, Padan E, Schuldiner S. Kinetic properties of NhaB, a Na+/H+ antiporter from Escherichia coli. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47190-6] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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38
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Padan E, Schuldiner S. Molecular physiology of Na+/H+ antiporters, key transporters in circulation of Na+ and H+ in cells. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1185:129-51. [PMID: 8167133 DOI: 10.1016/0005-2728(94)90204-6] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- E Padan
- Department of Microbial and Molecular Ecology, Hebrew University of Jerusalem, Israel
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39
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Padan E, Schuldiner S. Na+/H+ antiporters, molecular devices that couple the Na+ and H+ circulation in cells. J Bioenerg Biomembr 1993; 25:647-69. [PMID: 8144493 DOI: 10.1007/bf00770252] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Na+/H+ antiporters are universal devices involved in the Na+ and H+ circulation of both eukaryotes and prokaryotes, thus playing an essential role in the pH and Na+ homeostasis of cells. This review focuses on the major impact of the application of molecular biology tools in the study of the antiporters. These tools permit the verification of the role of the antiporters and provide insights into their unique biology. A novel signal transduction to Na+ involving nhaR, a positive regulator, controls the expression of nhaA in E. coli. A "pH sensor" regulates the activity of Na+/H+ antiporters, both in eukaryotes and prokaryotes. A most intricate signal transduction to pH involving phosphorylation steps controls the activity of nhel in higher mammals. The identification of Histidine 226 in the "pH sensor" of NhaA is a step forward towards the understanding of the pH regulation of these proteins.
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Affiliation(s)
- E Padan
- Division of Microbial and Molecular Ecology, Hebrew University of Jerusalem, Israel
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40
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Koyama N. Stimulatory effect of NH4+ on the transport of leucine and glucose in an anaerobic alkaliphile. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 217:435-9. [PMID: 8223582 DOI: 10.1111/j.1432-1033.1993.tb18263.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
An anaerobic alkaliphile, EP01, specifically requires NH4+ for the acceleration of amino acid and glucose transport [Koyama, N. (1988) FEBS Lett. 253, 187-189]. In this paper, we attempted to clarify how NH4+ is involved in the transport system. The bacterium acidifies the cytoplasm, which was suggested to result in NH4+ accumulation when NH4Cl was added to the medium. Increase of the NH4Cl concentration administered to the medium caused the acceleration of leucine and glucose transport, which was accompanied by an increase in the internal pH and the absolute internal concentration of NH4+, whereas a decrease in the concentration ratio of internal NH4+/external NH4+ was observed. The addition of 3 mM NH4Cl, which resulted in significant stimulation of leucine and glucose transport, raised the internal NH4+ concentration by 42 mM, but the internal pH only by 0.1 units. It seems more likely that leucine and glucose transport are accelerated depending on the increase in the internal NH4+ concentration rather than the increase in the internal pH. By the imposition of an inwardly directed Na+ gradient, the K(+)-loaded membrane vesicles accumulated leucine and glucose, indicating that a sodium chemical potential is available for active transport. The membrane of the bacterium exhibited a Na(+)-stimulated ATPase activity which was remarkably enhanced by the addition of NH4Cl, depending on its concentration, and was inhibited by vanadate. Leucine and glucose transport were inhibited by vanadate. Based on these results, we propose a mechanism in which NH4+ contributes internally to leucine and glucose transport, depending on its concentration, by the activation of a Na(+)-translocating ATPase responsible for the generation of a sodium chemical potential.
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Affiliation(s)
- N Koyama
- Chemistry Department, College of Arts and Sciences, Chiba University, Japan
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41
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Guihard G, Bénédetti H, Besnard M, Letellier L. Phosphate efflux through the channels formed by colicins and phage T5 in Escherichia coli cells is responsible for the fall in cytoplasmic ATP. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(17)46772-x] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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42
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Glaser TA, Mukkada AJ. Proline transport in Leishmania donovani amastigotes: dependence on pH gradients and membrane potential. Mol Biochem Parasitol 1992; 51:1-8. [PMID: 1533014 DOI: 10.1016/0166-6851(92)90194-o] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Amastigotes of Leishmania donovani develop and multiply within the acidic phagolysosomes of mammalian macrophages. Isolated amastigotes are acidophilic; they catabolize substrates and synthesize macromolecules optimally at pH 5.5. Substrate transport in amastigotes has not been characterized. Here we show that amastigotes exhibit an uphill transport of proline (active transport) with an acid pH optimum (pH 5.5). It is dependent upon metabolic energy and is driven by proton motive force. Agents which selectively disturb the component forces of proton motive force, such as carbonyl cyanide chlorophenylhydrazone, nigericin and valinomycin, inhibit proline transport. Transport is sensitive to dicyclohexylcarbodiimide and insensitive to ouabain, demonstrating the involvement of a proton ATPase in the maintenance of proton motive force. It is suggested that the plasma membrane pH gradient probably makes the greatest contribution to proton motive force that drives substrate transport in the amastigote stage.
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Affiliation(s)
- T A Glaser
- Department of Biological Sciences, University of Cincinnati, OH 45221
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43
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Bröer S, Krämer R. Lysine excretion by Corynebacterium glutamicum. 2. Energetics and mechanism of the transport system. EUROPEAN JOURNAL OF BIOCHEMISTRY 1991; 202:137-43. [PMID: 1657604 DOI: 10.1111/j.1432-1033.1991.tb16354.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Lysine excretion in Corynebacterium glutamicum was characterized as secondary transport process. It is modulated by three forces: the membrane potential, the chemical potential of lysine, and the proton gradient. The ATP content of the cells did not correlate with the export activity. Lysine is excreted in symport with presumably two OH- ions which is not distinguishable experimentally from an antiport mechanism against two protons. The substrate-loaded carrier is uncharged. When the external substrate concentration is low and no proton gradient present, reorientation of the positively charged, unloaded carrier is rate-limiting. Export then depends on the membrane potential. When the external substrate is high, translocation of the loaded, uncharged carrier is rate-limiting, and export is not modulated by the membrane potential. The lysine secretion system in C. glutamicum is shown to be well adapted to the requirements of metabolite export.
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Affiliation(s)
- S Bröer
- Institut für Biotechnologie I, Forschungszentrum Jülich, Federal Republic of Germany
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44
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Bakker EP. The role of alkali-cation transport in energy coupling of neutrophilic and acidophilic bacteria: An assessment of methods and concepts. FEMS Microbiol Lett 1990. [DOI: 10.1111/j.1574-6968.1990.tb04105.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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45
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Effects of pH, glucose, and chelating agents on lethality of paraquat to Escherichia coli. J Bacteriol 1990; 172:691-5. [PMID: 2404952 PMCID: PMC208494 DOI: 10.1128/jb.172.2.691-695.1990] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Retention of paraquat by Escherichia coli B was greatest after exposure at pH 9.0 and was progressively less after exposure at pH 7.0 and 5.0, respectively. This retained paraquat was capable of persistent growth inhibition. Uptake and retention of paraquat by E. coli B was dependent upon a carbon source, such as glucose. Under comparable conditions E. coli K-12 did not retain paraquat. The lethality of paraquat was seen in TSY medium but not in VB medium. The addition of Soytone, tryptone, or yeast extract, to the VB medium allowed the lethality of paraquat to be seen. A variety of chelating agents, including EDTA, 8-hydroxyquinoline, and o-phenanthroline, prevented the lethal effect of paraquat in TSY medium. Although EDTA protected against the lethality of paraquat, it did not protect against its bacteriostatic effect.
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46
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Toxicity of volatile fatty acids at rumen pH prevents enrichment ofEscherichia coli by sorbitol in rumen contents. Curr Microbiol 1989. [DOI: 10.1007/bf01570101] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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47
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Flatau GN, Clément RL, Mahdyoun F, Leblanc G, Gauthier MJ. Role of transmembrane electrical potential on cadmium fixation by a marine pseudomonad. Res Microbiol 1989; 140:553-62. [PMID: 2623367 DOI: 10.1016/0923-2508(89)90087-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The role of cellular energy, and mainly that of electrical transmembrane potential, in cadmium fixation by a marine pseudomonad suspended in a mineral medium was investigated by studying the effects of ionophores. Although fixation of cadmium by cells was generally less when respiratory activity was inhibited, it was not affected by a reduction of the transmembrane electrical potential delta psi in mureinoplasts. These observations strongly suggest that cadmium fixation in this isolate was not the result of a delta psi-dependent active transport.
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Affiliation(s)
- G N Flatau
- Institut National de la Santé et de la Recherche Médicale (INSERM), Unité 303 Mer et Santé, Nice, France
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48
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Zafra F, Giménez C. The role of chloride ions on the transport of glycine in plasma membrane vesicles from glial cells. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 979:147-52. [PMID: 2923873 DOI: 10.1016/0005-2736(89)90429-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The high-affinity transport system for glycine in plasma membrane vesicles from C6 glioma cells is dependent on Na+ and also on the presence of Cl- in the incubation medium. This anion requirement is relatively specific for Cl-, since other anions are also capable of stimulating the glycine transport in the following order of decreasing efficacy: Cl- greater than Br- greater than SCN- congruent to I- greater than NO3- greater than F-. Chloride ions raise the Vmax for transport and, to a lesser extent, act on the Km. The data provided by direct measurements of the coupling of sodium and chloride to the transport of glycine by using a kinetic approach suggest a stoichiometry for the translocation cycle catalyzed by the glycine transporter of two sodium ions and one chloride ion per glycine zwitterion.
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Affiliation(s)
- F Zafra
- Departamento de Bioloía Molecular, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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49
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Dornmair K, Overath P, Jähnig F. Fast Measurement of Galactoside Transport by Lactose Permease. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(17)31263-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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50
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Abee T, Hellingwerf KJ, Konings WN. Effects of potassium ions on proton motive force in Rhodobacter sphaeroides. J Bacteriol 1988; 170:5647-53. [PMID: 3263963 PMCID: PMC211664 DOI: 10.1128/jb.170.12.5647-5653.1988] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The proton motive force (PMF) was determined in Rhodobacter sphaeroides under anaerobic conditions in the dark and under aerobic-dark and anaerobic-light conditions. Anaerobically in the dark in potassium phosphate buffer, the PMF at pH 6 was -20 mV and was composed of an electrical potential (delta psi) only. At pH 7.9 the PMF was composed of a high delta psi of -98 mV and was partially compensated by a reversed pH gradient (delta pH) of +37 mV. ATPase inhibitors did not affect the delta psi, which was most likely the result of a K+ diffusion potential. Under energized conditions in the presence of K+ the delta psi depolarized due to electrogenic K+ uptake. This led to the generation of a delta pH (inside alkaline) in the external pH range of 6 to 8. This delta pH was dependent on the K+ concentration and was maximal at external K+ concentrations larger than 1.2 mM. In energized cells in 50 mM KPi buffer containing 5 mM MgSO4, a delta pH (inside alkaline) was present at external pHs from pH 6 to 8. As a result the overall magnitude of the PMF at various external pHs remained constant at -130 mV, which was significantly higher than the PMF under anaerobic-dark conditions. In the absence of K+, in 50 mM NaPi buffer containing 5 mM MgSO4, no depolarization of the delta psi was found and the PMF was composed of a large delta psi and a small delta pH. The delta pH became even reversed (inside acidic) at alkaline pHs (pH>7.3), resulting in a lowering of the PMF. These results demonstrate that in R. sphaeroides K+ uptake is essential for the generation of a delta pH and plays a central role in the regulation of the internal pH.
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Affiliation(s)
- T Abee
- Department of Microbiology, University of Groningen, Haren, The Netherlands
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