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Wnek GE, Costa ACS, Kozawa SK. Bio-Mimicking, Electrical Excitability Phenomena Associated With Synthetic Macromolecular Systems: A Brief Review With Connections to the Cytoskeleton and Membraneless Organelles. Front Mol Neurosci 2022; 15:830892. [PMID: 35321030 PMCID: PMC8937024 DOI: 10.3389/fnmol.2022.830892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 01/11/2022] [Indexed: 11/13/2022] Open
Abstract
Electrical excitability of cells, tissues and organs is a fundamental phenomenon in biology and physiology. Signatures of excitability include transient currents resulting from a constant or varying voltage gradient across compartments. Interestingly, such signatures can be observed with non-biologically-derived, macromolecular systems. Initial key literature, dating to roughly the late 1960’s into the early 1990’s, is reviewed here. We suggest that excitability in response to electrical stimulation is a material phenomenon that is exploited by living organisms, but that is not exclusive to living systems. Furthermore, given the ubiquity of biological hydrogels, we also speculate that excitability in protocells of primordial organisms might have shared some of the same molecular mechanisms seen in non-biological macromolecular systems, and that vestigial traces of such mechanisms may still play important roles in modern organisms’ biological hydrogels. Finally, we also speculate that bio-mimicking excitability of synthetic macromolecular systems might have practical biomedical applications.
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Affiliation(s)
- Gary E. Wnek
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH, United States
- *Correspondence: Gary E. Wnek,
| | - Alberto C. S. Costa
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH, United States
- Department of Psychiatry, Case Western Reserve University, Cleveland, OH, United States
- Alberto C. S. Costa,
| | - Susan K. Kozawa
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH, United States
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2
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Golubchik A, Lopes LC, Singh V, Kuss S. Pharma‐molecule Transport across Bacterial Membranes: Detection and Quantification Approaches by Electrochemistry and Bioanalytical Methods. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202101055] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Alon Golubchik
- Department Chemistry University of Manitoba Winnipeg R3T 2N2 Canada
| | | | - Vikram Singh
- Department Chemistry University of Manitoba Winnipeg R3T 2N2 Canada
| | - Sabine Kuss
- Department Chemistry University of Manitoba Winnipeg R3T 2N2 Canada
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3
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Golubchik A, Lopes LC, Singh V, Kuss S. Pharma-molecule Transport across Bacterial Membranes: Detection and Quantification Approaches by Electrochemistry and Bioanalytical Methods. Angew Chem Int Ed Engl 2021; 60:22112-22124. [PMID: 33979000 DOI: 10.1002/anie.202101055] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Indexed: 11/07/2022]
Abstract
Antibiotic resistance is a significant challenge encountered by healthcare systems on a global scale. Knowledge about membrane transport of antibiotics and other pharmacologically relevant molecules in bacteria is crucial towards understanding and overcoming antibiotic resistance, as drug resistance often depends on drug transport. This comprehensive literature review discusses the detection and quantification of membrane transport of pharma-molecules in bacteria and highlights the importance of molecule transport to antibiotic resistance. This review emphasizes electrochemical and electrophysiological methods of detection and quantification. The results of this literature review reveal a substantial diversity in methods and types of quantitative information collected.
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Affiliation(s)
- Alon Golubchik
- Department Chemistry, University of Manitoba, Winnipeg, R3T 2N2, Canada
| | | | - Vikram Singh
- Department Chemistry, University of Manitoba, Winnipeg, R3T 2N2, Canada
| | - Sabine Kuss
- Department Chemistry, University of Manitoba, Winnipeg, R3T 2N2, Canada
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4
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Life with Bacterial Mechanosensitive Channels, from Discovery to Physiology to Pharmacological Target. Microbiol Mol Biol Rev 2020; 84:84/1/e00055-19. [PMID: 31941768 DOI: 10.1128/mmbr.00055-19] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
General principles in biology have often been elucidated from the study of bacteria. This is true for the bacterial mechanosensitive channel of large conductance, MscL, the channel highlighted in this review. This channel functions as a last-ditch emergency release valve discharging cytoplasmic solutes upon decreases in osmotic environment. Opening the largest gated pore, MscL passes molecules up to 30 Å in diameter; exaggerated conformational changes yield advantages for study, including in vivo assays. MscL contains structural/functional themes that recur in higher organisms and help elucidate how other, structurally more complex, channels function. These features of MscL include (i) the ability to directly sense, and respond to, biophysical changes in the membrane, (ii) an α helix ("slide helix") or series of charges ("knot in a rope") at the cytoplasmic membrane boundary to guide transmembrane movements, and (iii) important subunit interfaces that, when disrupted, appear to cause the channel to gate inappropriately. MscL may also have medical applications: the modality of the MscL channel can be changed, suggesting its use as a triggered nanovalve in nanodevices, including those for drug targeting. In addition, recent studies have shown that the antibiotic streptomycin opens MscL and uses it as one of the primary paths to the cytoplasm. Moreover, the recent identification and study of novel specific agonist compounds demonstrate that the channel is a valid drug target. Such compounds may serve as novel-acting antibiotics and adjuvants, a way of permeabilizing the bacterial cell membrane and, thus, increasing the potency of commonly used antibiotics.
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5
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Wray R, Herrera N, Iscla I, Wang J, Blount P. An agonist of the MscL channel affects multiple bacterial species and increases membrane permeability and potency of common antibiotics. Mol Microbiol 2019; 112:896-905. [PMID: 31177589 PMCID: PMC6736685 DOI: 10.1111/mmi.14325] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/06/2019] [Indexed: 12/18/2022]
Abstract
The bacterial MscL channel normally functions as an emergency release valve discharging cytoplasmic solutes upon osmotic stress. The channel opens and passes molecules up to 30 Å and its pore is the largest of any gated channel. Opening the MscL pore inappropriately is detrimental to the bacterial cell, suggesting MscL as a potential novel drug target. A small-molecule compound, 011A, has been shown to increase sensitivity of the Escherichia coli MscL channel, slow growth, and even decrease viability of quiescent cultures. The mscL gene is highly conserved and found in the vast majority of bacterial species, including pathogens. Here, we test the hypothesis that 011A can influence the growth and viability of other bacterial species, specifically Staphylococcus aureus and Mycobacterium smegmatis, in a MscL-dependent manner. Furthermore, we demonstrate that the 011A compound can increase potency of other antibiotics, presumably by permeabilizing the membrane and allowing easier access of the antibiotic into the cytoplasm. Thus, MscL activators have potential as novel broad-spectrum antibiotics or adjuvants that work with antibiotics to selectively allow passage across bacterial membranes.
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Affiliation(s)
- Robin Wray
- Department of Physiology, UT Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX
| | - Nadia Herrera
- Division of Chemistry and Chemical Engineering 114-96, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA
| | - Irene Iscla
- Department of Physiology, UT Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX
| | - Junmei Wang
- Department of Pharmaceutical Sciences, University of Pittsburgh School of Pharmacy
| | - Paul Blount
- Department of Physiology, UT Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX
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6
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Wilson ME, Maksaev G, Haswell ES. MscS-like mechanosensitive channels in plants and microbes. Biochemistry 2013; 52:5708-22. [PMID: 23947546 DOI: 10.1021/bi400804z] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The challenge of osmotic stress is something all living organisms must face as a result of environmental dynamics. Over the past three decades, innovative research and cooperation across disciplines have irrefutably established that cells utilize mechanically gated ion channels to release osmolytes and prevent cell lysis during hypoosmotic stress. Early electrophysiological analysis of the inner membrane of Escherichia coli identified the presence of three distinct mechanosensitive activities. The subsequent discoveries of the genes responsible for two of these activities, the mechanosensitive channels of large (MscL) and small (MscS) conductance, led to the identification of two diverse families of mechanosensitive channels. The latter of these two families, the MscS family, consists of members from bacteria, archaea, fungi, and plants. Genetic and electrophysiological analysis of these family members has provided insight into how organisms use mechanosensitive channels for osmotic regulation in response to changing environmental and developmental circumstances. Furthermore, determining the crystal structure of E. coli MscS and several homologues in several conformational states has contributed to our understanding of the gating mechanisms of these channels. Here we summarize our current knowledge of MscS homologues from all three domains of life and address their structure, proposed physiological functions, electrophysiological behaviors, and topological diversity.
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Affiliation(s)
- Margaret E Wilson
- Department of Biology, Washington University in St. Louis, Missouri 63130, United States
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7
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Naismith JH, Booth IR. Bacterial mechanosensitive channels--MscS: evolution's solution to creating sensitivity in function. Annu Rev Biophys 2012; 41:157-77. [PMID: 22404681 PMCID: PMC3378650 DOI: 10.1146/annurev-biophys-101211-113227] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The discovery of mechanosensing channels has changed our understanding of bacterial physiology. The mechanosensitive channel of small conductance (MscS) is perhaps the most intensively studied of these channels. MscS has at least two states: closed, which does not allow solutes to exit the cytoplasm, and open, which allows rapid efflux of solvent and solutes. The ability to appropriately open or close the channel (gating) is critical to bacterial survival. We briefly review the science that led to the isolation and identification of MscS. We concentrate on the structure-function relationship of the channel, in particular the structural and biochemical approaches to understanding channel gating. We highlight the troubling discrepancies between the various models developed to understand MscS gating.
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Affiliation(s)
- James H. Naismith
- Professor Chemical Biology, Biomedical Sciences Research Complex, The North Haugh, The University, St Andrews, Fife KY16 9ST, United Kingdom;
| | - Ian R. Booth
- Professor Emeritus Microbiology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, AB25 2ZD, United Kingdom;
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8
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Cloning and functional expression of an MscL ortholog from Rhizobium etli: characterization of a mechanosensitive channel. J Membr Biol 2010; 234:13-27. [PMID: 20177670 DOI: 10.1007/s00232-010-9235-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 01/26/2010] [Indexed: 10/19/2022]
Abstract
Rhizobium etli is equipped with several systems to handle both hyper- and hypo-osmotic stress. For adaptation to hypo-osmotic stress, R. etli possesses a single gene with clear homology to MscS, four MscS-like channels and one ortholog of MscL (ReMscL, identity approximately 44% compared to Escherichia coli MscL). We subcloned and expressed the ReMscL channel ortholog from R. etli in E. coli to examine its activity by patch clamp in giant spheroplasts and characterized it at the single-channel level. We obtained evidence that ReMscL prevents the lysis of E. coli null mutant log-phase cells upon a rapid, osmotic downshock and identified a slight pH dependence for ReMscL activation. Here, we describe the facilitation of ReMscL activation by arachidonic acid (AA) and a reversible inhibitory effect of Gd(3+). The results obtained in these experiments suggest a stabilizing effect of micromolar AA and traces of Gd(3+) ions in the partially expanded conformation of the protein. Finally, we discuss a possible correlation between the number of gene paralogs for MS channels and the habitats of several microorganisms. Taken together, our data show that ReMscL may play an important role in free-living rhizobacteria during hypo-osmotic shock in the rhizosphere.
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9
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Pivetti CD, Yen MR, Miller S, Busch W, Tseng YH, Booth IR, Saier MH. Two families of mechanosensitive channel proteins. Microbiol Mol Biol Rev 2003; 67:66-85, table of contents. [PMID: 12626684 PMCID: PMC150521 DOI: 10.1128/mmbr.67.1.66-85.2003] [Citation(s) in RCA: 174] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mechanosensitive (MS) channels that provide protection against hypoosmotic shock are found in the membranes of organisms from the three domains of life: bacteria, archaea, and eucarya. Two families of ubiquitous MS channels are recognized, and these have been designated the MscL and MscS families. A high-resolution X-ray crystallographic structure is available for a member of the MscL family, and extensive molecular genetic, biophysical, and biochemical studies conducted in many laboratories have allowed postulation of a gating mechanism allowing the interconversion of a tightly closed state and an open state that controls transmembrane ion and metabolite fluxes. In contrast to the MscL channel proteins, which are of uniform topology, the much larger MscS family includes protein members with topologies that are predicted to vary from 3 to 11 alpha-helical transmembrane segments (TMSs) per polypeptide chain. Sequence analyses reveal that the three C-terminal TMSs of MscS channel proteins are conserved among family members and that the third of these three TMSs exhibits a 20-residue motif that is shared by the channel-forming TMS (TMS 1) of the MscL proteins. We propose that this C-terminal TMS in MscS family homologues serves as the channel-forming helix in a homooligomeric structure. The presence of a conserved residue pattern for the putative channel-forming TMSs in the MscL and MscS family proteins suggests a common structural organization, gating mechanism, and evolutionary origin.
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Affiliation(s)
- Christopher D Pivetti
- Division of Biology, University of California San Diego, La Jolla, California 92093-0116, USA
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10
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Sleator RD, Hill C. Bacterial osmoadaptation: the role of osmolytes in bacterial stress and virulence. FEMS Microbiol Rev 2002; 26:49-71. [PMID: 12007642 DOI: 10.1111/j.1574-6976.2002.tb00598.x] [Citation(s) in RCA: 480] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Two general strategies exist for the growth and survival of prokaryotes in environments of elevated osmolarity. The 'salt in cytoplasm' approach, which requires extensive structural modifications, is restricted mainly to members of the Halobacteriaceae. All other species have convergently evolved to cope with environments of elevated osmolarity by the accumulation of a restricted range of low molecular mass molecules, termed compatible solutes owing to their compatibility with cellular processes at high internal concentrations. Herein we review the molecular mechanisms governing the accumulation of these compounds, both in Gram-positive and Gram-negative bacteria, focusing specifically on the regulation of their transport/synthesis systems and the ability of these systems to sense and respond to changes in the osmolarity of the extracellular environment. Finally, we examine the current knowledge on the role of these osmostress responsive systems in contributing to the virulence potential of a number of pathogenic bacteria.
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Affiliation(s)
- Roy D Sleator
- Department of Microbiology and National Food Biotechnology Centre, University College Cork, Cork, Ireland
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11
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Abstract
The simplest cell-like structure, the lipid bilayer vesicle, can respond to mechanical deformation by elastic membrane dilation/thinning and curvature changes. When a protein is inserted in the lipid bilayer, an energetic cost may arise because of hydrophobic mismatch between the protein and bilayer. Localized changes in bilayer thickness and curvature may compensate for this mismatch. The peptides alamethicin and gramicidin and the bacterial membrane protein MscL form mechanically gated (MG) channels when inserted in lipid bilayers. Their mechanosensitivity may arise because channel opening is associated with a change in the protein's membrane-occupied area, its hydrophobic mismatch with the bilayer, excluded water volume, or a combination of these effects. As a consequence, bilayer dilation/thinning or changes in local membrane curvature may shift the equilibrium between channel conformations. Recent evidence indicates that MG channels in specific animal cell types (e.g., Xenopus oocytes) are also gated directly by bilayer tension. However, animal cells lack the rigid cell wall that protects bacteria and plants cells from excessive expansion of their bilayer. Instead, a cortical cytoskeleton (CSK) provides a structural framework that allows the animal cell to maintain a stable excess membrane area (i.e., for its volume occupied by a sphere) in the form of membrane folds, ruffles, and microvilli. This excess membrane provides an immediate membrane reserve that may protect the bilayer from sudden changes in bilayer tension. Contractile elements within the CSK may locally slacken or tighten bilayer tension to regulate mechanosensitivity, whereas membrane blebbing and tight seal patch formation, by using up membrane reserves, may increase membrane mechanosensitivity. In specific cases, extracellular and/or CSK proteins (i.e., tethers) may transmit mechanical forces to the process (e.g., hair cell MG channels, MS intracellular Ca(2+) release, and transmitter release) without increasing tension in the lipid bilayer.
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Affiliation(s)
- O P Hamill
- Physiology and Biophysics, University Of Texas Medical Branch, Galveston, Texas 77555, USA.
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12
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Moe PC, Levin G, Blount P. Correlating a protein structure with function of a bacterial mechanosensitive channel. J Biol Chem 2000; 275:31121-7. [PMID: 10846181 DOI: 10.1074/jbc.m002971200] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MscL, a mechanosensitive channel found in many bacteria, protects cells from hypotonic shock by reducing intracellular pressure through release of cytoplasmic osmolytes. First isolated from Escherichia coli, this protein has served as a model for how a protein senses and responds to membrane tension. Recently the structure of a functionally uncharacterized MscL homologue from Mycobacterium tuberculosis was solved by x-ray diffraction to a resolution of 3.5 A. Here we demonstrate that the protein forms a functional MscL-like mechanosensitive channel in E. coli membranes and azolectin proteoliposomes. Furthermore, we show that M. tuberculosis MscL crystals, when re-solubilized and reconstituted, yield wild-type channel currents in patch clamp, demonstrating that the protein does not irreversibly change conformation upon crystallization. Finally, we apply functional clues acquired from the E. coli MscL to the M. tuberculosis channel and show a mechanistic correlation between these channels. However, the inability of the M. tuberculosis channel to gate at physiological membrane tensions, demonstrated by in vivo E. coli expression and in vitro reconstitution, suggests that the membrane environment or other additional factors influence the gating of this channel.
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Affiliation(s)
- P C Moe
- Department of Physiology, University of Texas-Southwestern Medical Center, Dallas, Texas 75390-9040, USA
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13
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Levina N, Tötemeyer S, Stokes NR, Louis P, Jones MA, Booth IR. Protection of Escherichia coli cells against extreme turgor by activation of MscS and MscL mechanosensitive channels: identification of genes required for MscS activity. EMBO J 1999; 18:1730-7. [PMID: 10202137 PMCID: PMC1171259 DOI: 10.1093/emboj/18.7.1730] [Citation(s) in RCA: 549] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mechanosensitive channels are ubiquitous amongst bacterial cells and have been proposed to have major roles in the adaptation to osmotic stress, in particular in the management of transitions from high to low osmolarity environments. Electrophysiological measurements have identified multiple channels in Escherichia coli cells. One gene, mscL, encoding a large conductance channel has previously been described, but null mutants were without well-defined phenotypes. Here, we report the characterization of a new gene family required for MscS function, YggB and KefA, which has enabled a rigorous test of the role of the channels. The channel determined by KefA does not appear to have a major role in managing the transition from high to low osmolarity. In contrast, analysis of mutants of E.coli lacking YggB and MscL shows that mechanosensitive channels are designed to open at a pressure change just below that which would cause cell disruption leading to death.
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Affiliation(s)
- N Levina
- Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK
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14
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Ruffert S, Berrier C, Krämer R, Ghazi A. Identification of mechanosensitive ion channels in the cytoplasmic membrane of Corynebacterium glutamicum. J Bacteriol 1999; 181:1673-6. [PMID: 10049402 PMCID: PMC93560 DOI: 10.1128/jb.181.5.1673-1676.1999] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Patch-clamp experiments performed on membrane fragments of Corynebacterium glutamicum fused into giant liposomes revealed the presence of two different stretch-activated conductances, 600 to 700 pS and 1,200 to 1,400 pS in 0.1 M KCl, that exhibited the same characteristics in terms of kinetics, ion selectivity, and voltage dependence.
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Affiliation(s)
- S Ruffert
- Institut für Biochemie, Universität zu Köln, 50674 Köln, Germany
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15
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Affiliation(s)
- P Blount
- Department of Physiology, University of Texas, Southwestern Medical Center, Dallas 75235, USA
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16
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Moe PC, Blount P, Kung C. Functional and structural conservation in the mechanosensitive channel MscL implicates elements crucial for mechanosensation. Mol Microbiol 1998; 28:583-92. [PMID: 9632260 DOI: 10.1046/j.1365-2958.1998.00821.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
mscL encodes a channel in Escherichia coli that is opened by membrane stretch force, probably serving as an osmotic gauge. Sequences more or less similar to mscL are found in other bacteria, but the degree of conserved function has been unclear. We subcloned and expressed these putative homologues in E. coli and examined their products under patch clamp. Here, we show that each indeed encodes a conserved mechanosensitive channel activity, consistent with the interpretation that this is an important and primary function of the protein in a wide range of bacteria. Although similar, channels of different bacteria differ in kinetics and their degree of mechanosensitivity. Comparison of the primary sequence of these proteins reveals two highly conserved regions, corresponding to domains previously shown to be important for the function of the wild-type E. coli channel, and a C-terminal region that is not conserved in all species. This structural conservation is providing insight into regions of this molecule that are vital to its role as a mechanosensitive channel and may have broader implications for the understanding of other mechanosensitive systems.
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Affiliation(s)
- P C Moe
- Laboratory of Molecular Biology and Department of Bacteriology, University of Wisconsin-Madison, 53706, USA
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17
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Blount P, Schroeder MJ, Kung C. Mutations in a bacterial mechanosensitive channel change the cellular response to osmotic stress. J Biol Chem 1997; 272:32150-7. [PMID: 9405414 DOI: 10.1074/jbc.272.51.32150] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
MscL is a channel found in bacterial plasma membranes that opens a large pore in response to mechanical stress. Here we demonstrate that some mutations within this channel protein (K31D and K31E) evoke a cellular phenotype in which the growth rate is severely depressed. Increasing the osmolarity of the growth medium partially rescues this "slowed growth" phenotype and decreases an abnormal cytosolic potassium loss observed in cells expressing the mutants. In addition, upon sudden decrease in osmolarity (osmotic downshock) more cytoplasmic potassium is released from cells expressing the mutants than cells expressing wild-type MscL. After osmotic downshock, all cells remained viable; hence, the differences in potassium efflux observed are not due to cell lysis but instead appear to be an exaggeration of the normal response to this sudden change in environmental osmolarity. Patch clamp studies in native bacterial membranes substantiate the hypothesis that these mutant channels are more sensitive to mechanical stresses, especially at voltages approaching those estimated for bacterial membrane potentials. These data are consistent with a crucial role for MscL in the adaptation to large osmotic downshock and suggest that if the normally tight regulation of MscL gating is disrupted, cell growth can be severely inhibited.
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Affiliation(s)
- P Blount
- Laboratory of Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706, USA.
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18
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Szabò I, Bàthori G, Tombola F, Brini M, Coppola A, Zoratti M. DNA translocation across planar bilayers containing Bacillus subtilis ion channels. J Biol Chem 1997; 272:25275-82. [PMID: 9312144 DOI: 10.1074/jbc.272.40.25275] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The mechanisms by which genetic material crosses prokaryotic membranes are incompletely understood. We have developed a new methodology to study the translocation of genetic material via pores in a reconstituted system, using techniques from electrophysiology and molecular biology. We report here that planar bilayer membranes become permeable to double-stranded DNA (kilobase range) if Bacillus subtilis membrane vesicles containing high conductance channels have been fused into them. The translocation is an electrophoretic process, since it does not occur if a transmembrane electrical field opposing the movement of DNA, a polyanion, is applied. It is not an aspecific permeation through the phospholipid bilayer, since it does not take place if no proteins have been incorporated into the membrane. The transport is also not due simply to the presence of polypeptides in the membrane, since it does not occur if the latter contains gramicidin A or a eukaryotic, multi-protein vesicle fraction exhibiting 30-picosiemens anion-selective channel activity. The presence of DNA alters the behavior of the bacterial channels, indicating that it interacts with the pores and may travel through their lumen. These results support the idea that DNA translocation may take place through proteic pores and suggest that some of the high conductance bacterial channels observed in electrophysiological experiments may be constituents of the DNA translocating machinery in these organisms.
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Affiliation(s)
- I Szabò
- CNR Unit for the Study of Biomembranes, Department of Biomedical Sciences, University of Padova, Viale G. Colombo 3, 35121 Padova, Italy
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19
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Besnard M, Martinac B, Ghazi A. Voltage-dependent porin-like ion channels in the archaeon Haloferax volcanii. J Biol Chem 1997; 272:992-5. [PMID: 8995393 DOI: 10.1074/jbc.272.2.992] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Membrane vesicles isolated from the cell envelope of the archaebacterium Haloferax volcanii were either reconstituted in giant liposomes and examined by the patch-clamp technique or were fused into planar lipid bilayers. In addition, cell envelope proteins were solubilized by detergent and reconstituted in azolectin liposomes, which were then fused into planar lipid bilayers. Independently of the technique used the predominant channel activity encountered exhibited the following characteristics. Channels were open at all voltages in the range approximately -120 to +120 mV and exhibited frequent fast transitions to closed levels of different amplitudes. At voltages greater than 120 mV the channels tended to close in a manner characterized by large, slow transitions of variable amplitudes. The tendency to close at high membrane potentials was much stronger at one polarity. The channel gating pattern was complex exhibiting a range of subconductances of 10-300 picosiemens in symmetric 100 mM KCl. These electrophysiological characteristics are comparable with those of bacterial and mitochondrial porins, suggesting that the archaeal channels may belong to the general class of porin channels. Some channels showed preference for K+, whereas the others preferred Cl-, suggesting the existence of at least two types of porin-like channels in H. volcanii.
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Affiliation(s)
- M Besnard
- Laboratoire des Biomembranes, URA CNRS 1116, Université Paris-Sud, Orsay, France
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Sukharev SI, Blount P, Martinac B, Kung C. Mechanosensitive channels of Escherichia coli: the MscL gene, protein, and activities. Annu Rev Physiol 1997; 59:633-57. [PMID: 9074781 DOI: 10.1146/annurev.physiol.59.1.633] [Citation(s) in RCA: 243] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Although mechanosensory responses are ubiquitous and diverse, the molecular bases of mechanosensation in most cases remain mysterious MscL, a mechanosensitive channel of large conductance of Escherichia coli and its bacterial homologues are the first and currently only channel molecules shown to directly sense mechanical stretch of the membrane. In response to the tension conveyed via the lipid bilayer, MscL increases its open probability by several orders of magnitude. In the present review we describe the identification, cloning, and first sets of biophysical and structural data on this simplest mechanosensory molecule. We discovered a 2.5-ns mechanosensitive conductance in giant E. coli spheroplasts. Using chromatographies to enrich the target and patch clamp to assay the channel activity in liposome-reconstituted fractions, we identified the MscL protein and cloned the mscL gene. MscL comprises 136 amino acid residues (15 kDa), with two highly hydrophobic regions, and resides in the inner membrane of the bacterium. PhoA-fusion experiments indicate that the protein spans the membrane twice with both termini in the cytoplasm. Spectroscopic techniques show that it is highly helical. Expression of MscL tandems and covalent cross-linking suggest that the active channel complex is a homo-hexamer. We have identified several residues, which when deleted or substituted, affect channel kinetics or mechanosensitivity. Although unique when discovered, highly conserved MscL homologues in both gram-negative and gram-positive bacteria have been found, suggesting their ubiquitous importance among bacteria.
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Affiliation(s)
- S I Sukharev
- Laboratory of Molecular Biology, University of Wisconsin, Madison 53706, USA
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Blount P, Sukharev SI, Schroeder MJ, Nagle SK, Kung C. Single residue substitutions that change the gating properties of a mechanosensitive channel in Escherichia coli. Proc Natl Acad Sci U S A 1996; 93:11652-7. [PMID: 8876191 PMCID: PMC38113 DOI: 10.1073/pnas.93.21.11652] [Citation(s) in RCA: 172] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
MscL is a channel that opens a large pore in the Escherichia coli cytoplasmic membrane in response to mechanical stress. Previously, we highly enriched the MscL protein by using patch clamp as a functional assay and cloned the corresponding gene. The predicted protein contains a largely hydrophobic core spanning two-thirds of the molecule and a more hydrophilic carboxyl terminal tail. Because MscL had no homology to characterized proteins, it was impossible to predict functional regions of the protein by simple inspection. Here, by mutagenesis, we have searched for functionally important regions of this molecule. We show that a short deletion from the amino terminus (3 amino acids), and a larger deletion of 27 amino acids from the carboxyl terminus of this protein, had little if any effect in channel properties. We have thus narrowed the search of the core mechanosensitive mechanism to 106 residues of this 136-amino acid protein. In contrast, single residue substitutions of a lysine in the putative first transmembrane domain or a glutamine in the periplasmic loop caused pronounced shifts in the mechano-sensitivity curves and/or large changes in the kinetics of channel gating, suggesting that the conformational structure in these regions is critical for normal mechanosensitive channel gating.
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Affiliation(s)
- P Blount
- Laboratory of Molecular Biology, University of Wisconsin, Madison 53706, USA
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Kinnally KW, Lohret TA, Campo ML, Mannella CA. Perspectives on the mitochondrial multiple conductance channel. J Bioenerg Biomembr 1996; 28:115-23. [PMID: 9132409 DOI: 10.1007/bf02110641] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A multiple conductance channel (MCC) with a peak conductance of over 1 nS is recorded from mitoplasts (mitochondria with the inner membrane exposed) using patch-clamp techniques. MCC shares many general characteristics with other intracellular megachannels, many of which are weakly selective, voltage-dependent, and calcium sensitive. A role in protein import is suggested by the transient blockade of MCC by peptides responsible for targeting mitochondrial precursor proteins. MCC is compared with the peptide-sensitive channel of the outer membrane because of similarities in targeting peptide blockade. The pharmacology and regulation of MCC by physiological effectors are reviewed and compared with the properties of the pore hypothesized to be responsible for the mitochondrial inner membrane permeability transition.
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Affiliation(s)
- K W Kinnally
- Division of Molecular Medicine, Wadsworth Center, Empire State Plaza, Albany, New York 12201-0509, USA
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