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Boris Martinac - One of the best experts on this subject based on the ideXlab platform.

  • cyclodextrins increase membrane tension and are universal activators of Mechanosensitive Channels
    Proceedings of the National Academy of Sciences of the United States of America, 2021
    Co-Authors: Boris Martinac, Charles D Cox, Yixiao Zhang, Zijing Zhou, Thomas Walz
    Abstract:

    The bacterial Mechanosensitive channel of small conductance (MscS) has been extensively studied to understand how mechanical forces are converted into the conformational changes that underlie Mechanosensitive (MS) channel gating. We showed that lipid removal by β-cyclodextrin can mimic membrane tension. Here, we show that all cyclodextrins (CDs) can activate reconstituted Escherichia coli MscS, that MscS activation by CDs depends on CD-mediated lipid removal, and that the CD amount required to gate MscS scales with the channel's sensitivity to membrane tension. Importantly, cholesterol-loaded CDs do not activate MscS. CD-mediated lipid removal ultimately causes MscS desensitization, which we show is affected by the lipid environment. While many MS Channels respond to membrane forces, generalized by the "force-from-lipids" principle, their different molecular architectures suggest that they use unique ways to convert mechanical forces into conformational changes. To test whether CDs can also be used to activate other MS Channels, we chose to investigate the Mechanosensitive channel of large conductance (MscL) and demonstrate that CDs can also activate this structurally unrelated channel. Since CDs can open the least tension-sensitive MS channel, MscL, they should be able to open any MS channel that responds to membrane tension. Thus, CDs emerge as a universal tool for the structural and functional characterization of unrelated MS Channels.

  • cyclodextrins increase membrane tension and are universal activators of Mechanosensitive Channels
    bioRxiv, 2021
    Co-Authors: Boris Martinac, Charles D Cox, Yixiao Zhang, Zijing Zhou, Thomas Walz
    Abstract:

    Abstract The bacterial Mechanosensitive channel of small conductance, MscS, has been extensively studied to understand how mechanical forces are converted into the conformational changes that underlie Mechanosensitive (MS) channel gating. We showed that lipid removal by β-cyclodextrin can mimic membrane tension. Here, we show that all cyclodextrins (CDs) can activate reconstituted E. coli MscS, that MscS activation by CDs depends on CD-mediated lipid removal, and that the CD amount required to gate MscS scales with the channel’s sensitivity to membrane tension. CD-mediated lipid removal ultimately causes MscS desensitization, which we show is affected by the lipid environment. CDs can also activate the structurally unrelated MscL. While many MS Channels respond to membrane forces, generalized by the ‘force-from-lipids’ principle, their different molecular architectures suggest that they use unique ways to convert mechanical forces into conformational changes. CDs emerge as a universal tool for the structural and functional characterization of unrelated MS Channels.

  • Mechanosensitive Channels of corynebacterium glutamicum functioning as exporters of l glutamate and other valuable metabolites
    Current Opinion in Chemical Biology, 2020
    Co-Authors: Hisashi Kawasaki, Boris Martinac
    Abstract:

    In the industrial l-glutamate production established on the use of Corynebacterium glutamicum, l-glutamate synthesized intracellularly is exported through Mechanosensitive transmembrane channel proteins (MscCG and MscCG2) activated by the force-from-lipids. The involvement of MscCG2 in l-glutamate export by C. glutamicum was demonstrated in 2018; however, MscCG was previously found to be the major exporter of l-glutamate. Recent advances in research methods, such as development of the microbial patch clamp, revealed unique characteristics of MscCG, including its conductance, opening and closing thresholds, and gating hysteresis, as well as the significant effect of membrane lipids on the channel properties. In addition, the cryoelectron microscopic structure of Escherichia coli MscS, the canonical representative of the Mechanosensitive channel family to which MscCG and MscCG2 belong, revealed its new membrane-interacting region, new position within the lipid bilayer, and hook lipids in a newly defined cavity between subunits. In this short review, the applications of bacterial Mechanosensitive Channels in the development of effective microbial cell factories, which will contribute to sustainable development, are discussed.

  • Piezo1 Mechanosensitive Channels: what are they and why are they important
    Biophysical Reviews, 2019
    Co-Authors: Pietro Ridone, Massimo Vassalli, Boris Martinac
    Abstract:

    Mechanosensitive (MS) ion Channels are integral membrane proteins which play a crucial role in fast signaling during mechanosensory transduction processes in living cells. They are ubiquitous and old in the evolutionary sense, given their presence in cells from all three kingdoms of life found on Earth, including bacterial, archaeal, and eukaryotic organisms. As molecular transducers of mechanical force, MS Channels are activated by mechanical stimuli exerted on cellular membranes, upon which they rapidly and efficiently convert these stimuli into electrical, osmotic, and/or chemical intracellular signals. Most of what we know about the gating mechanisms of MS Channels comes from the work carried out on bacterial Channels. However, recent progress resulting from identification and structural information of eukaryotic K2P-type TREK and TRAAK as well as Piezo1 and Piezo2 MS Channels has greatly contributed to our understanding of the common biophysical principles underlying the gating mechanism and evolutionary origins of these fascinating membrane proteins. Using Piezo1 Channels as an example, we briefly describe in this review what we have learned about their biophysics, physiological functions, and potential roles in “mechanopathologies.”

  • corynebacterium glutamicum Mechanosensitive Channels towards unpuzzling glutamate efflux for amino acid production
    Biophysical Reviews, 2018
    Co-Authors: Yoshitaka Nakayama, Boris Martinac, Kenichi Hashimoto, Yasuyuki Sawada, Masahiro Sokabe, Hisashi Kawasaki
    Abstract:

    Corynebacterium glutamicum has been utilized for industrial amino acid production, especially for monosodium glutamate (MSG), the food-additive for the “UMAMI” category of taste sensation, which is one of the five human basic tastes. Glutamate export from these cells is facilitated by the opening of Mechanosensitive Channels in the cell membrane within the bacterial cell envelope following specific treatments, such as biotin limitation, addition of Tween 40 or penicillin. A long-unsolved puzzle still remains how and why C. glutamicum Mechanosensitive Channels are activated by these treatments to export glutamate. Unlike Mechanosensitive Channels in other bacteria, these Channels are not simply osmotic safety valves that prevent these bacteria from bursting upon a hypo-osmotic shock. They also function as metabolic valves to continuously release glutamate as components of a pump-and-leak mechanism regulating the cellular turgor pressure. Recent studies have demonstrated that the opening of the Mechanosensitive channel, MscCG, mainly facilitates the efflux of glutamate and not of other amino acids and that the “force-from-lipids” gating mechanism of Channels also applies to the MscCG channel. The bacterial types of Mechanosensitive Channels are found in cell-walled organisms from bacteria to land plants, where their physiological functions have been specialized beyond their basic function in bacterial osmoregulation. In the case of the C. glutamicum MscCG Channels, they have evolved to function as specialized glutamate exporters.

Sergei Sukharev - One of the best experts on this subject based on the ideXlab platform.

  • a skin inspired soft material with directional mechanosensation
    Bioinspiration & Biomimetics, 2021
    Co-Authors: Michelle M Makhoulmansour, Elio J Challita, Adarsh Chaurasia, Donald J Leo, Sergei Sukharev, Eric C Freeman
    Abstract:

    Lessons about artificial sensor design may be taken from evolutionarily perfected physiological systems. Mechanosensory cells in human skin are exquisitely sensitive to gentle touch and enable us to distinguish objects of different stiffnesses and textures. These cells are embedded in soft epidermal layers of gel-like consistency. Reproducing these mechanosensing capabilities in new soft materials may lead to the development of adaptive mechanosensors which will further enhance the abilities of engineered membrane-based structures with bioinspired sensing strategies. This strategy is explored here using droplet interface bilayers embedded within a thermoreversible organogel. The interface between two lipid-coated aqueous inclusions contained within a soft polymeric matrix forms a lipid bilayer resembling the lipid matrix of cell membranes. These interfaces are functionalized with bacterial Mechanosensitive Channels (V23T MscL) which convert membrane tension into changes in membrane conductance, mimicking Mechanosensitive channel activation in mammalian mechanosensory cells. The distortion of encapsulated adhered droplets by cyclical external forces are first explored using a finite element composite model illustrating the directional propagation of mechanical disturbances imposed by a piston. The model predicts that the orientation of the droplet pair forming the membrane relative to the direction of the compression plays a role in the membrane response. The directional dependence of Mechanosensitive channel activation in response to gel compression is confirmed experimentally and shows that purely compressive perturbations normal to the interface invoke different channel activities as compared to shearing displacement along a plane of the membrane. The developed system containing specially positioned pairs of droplets functionalized with bacterial Mechanosensitive Channels and embedded in a gel creates a skin-inspired soft material with a directional response to mechanical perturbation.

  • effects of gsmtx4 on bacterial Mechanosensitive Channels in inside out patches from giant spheroplasts
    Biophysical Journal, 2010
    Co-Authors: Kishore Kamaraju, Philip A Gottlieb, Frederick Sachs, Sergei Sukharev
    Abstract:

    GsMTx4 is a 34-residue peptide isolated from the tarantula Grammostola spatulata folded into an inhibitory cysteine knot and it selectively affects gating of some Mechanosensitive Channels. Here we report the effects of cytoplasmic GsMTx4 on the two bacterial Channels, MscS and MscL, in giant Escherichia coli spheroplasts. In excised inside-out patches, GsMTx4 sensitized both Channels to tension by increasing the opening rate and decreasing the closing rate. With ascending and descending pressure ramps, GsMTx4 increased the gating hysteresis for MscS, a consequence of slower gating kinetics. Quantitative kinetic analysis of the primary C↔O transition showed that the hysteresis is a result of the decreased closing rate. The gating barrier location relative to the open state energy well was unaffected by GsMTx4. A reconstructed energy profile suggests that the peptide prestresses the resting state of MscS, lowering the net barrier to opening and stabilizes the open conformation by ∼8 kT. In excised patches, both MscL and MscS exhibit reversible adaptation, a process separable from inactivation for MscS. GsMTx4 decreased the rate of reversible adaptation for both Channels and the MscS recovery rate from the inactivation. These measurements support a mechanism where GsMTx4 binds to the lipid interface of the channel, increasing the local stress that is sensed by the Channels and stabilizing the expanded conformations.

  • Mechanosensitive Channels in microbes
    Annual Review of Microbiology, 2010
    Co-Authors: Ching Kung, Boris Martinac, Sergei Sukharev
    Abstract:

    All cells, including microbes, detect and respond to mechanical forces, of which osmotic pressure is most ancient and universal. Channel proteins have evolved such that they can be directly stretched open when the membrane is under turgor pressure. Osmotic downshock, as in rain, opens bacterial Mechanosensitive (MS) Channels to jettison osmolytes, relieving pressure and preventing cell lysis. The ion flux through individual channel proteins can be observed directly with a patch clamp. MS Channels of large and small conductance (MscL and MscS, respectively) have been cloned, crystallized, and subjected to biophysical and genetic analyses in depth. They are now models to scrutinize how membrane forces direct protein conformational changes. Eukaryotic microbes have homologs from animal sensory Channels of the TRP superfamily. The MS channel in yeast is also directly sensitive to membrane stretch. This review examines the key concept that proteins embedded in the lipid bilayer can respond to the changes in the mechanical environment the lipid bilayer provides.

  • adaptive behavior of bacterial Mechanosensitive Channels is coupled to membrane mechanics
    The Journal of General Physiology, 2010
    Co-Authors: Vladislav Belyy, Kishore Kamaraju, Andriy Anishkin, Bradley Akitake, Sergei Sukharev
    Abstract:

    Mechanosensitive channel of small conductance (MscS), a tension-driven osmolyte release valve residing in the inner membrane of Escherichia coli, exhibits a complex adaptive behavior, whereas its functional counterpart, Mechanosensitive channel of large conductance (MscL), was generally considered nonadaptive. In this study, we show that both Channels exhibit similar adaptation in excised patches, a process that is completely separable from inactivation prominent only in MscS. When a membrane patch is held under constant pressure, adaptation of both Channels is manifested as a reversible current decline. Their dose–response curves recorded with 1–10-s ramps of pressure are shifted toward higher tension relative to the curves measured with series of pulses, indicating decreased tension sensitivity. Prolonged exposure of excised patches to subthreshold tensions further shifts activation curves for both MscS and MscL toward higher tension with similar magnitude and time course. Whole spheroplast MscS recordings performed with simultaneous imaging reveal activation curves with a midpoint tension of 7.8 mN/m and the slope corresponding to ∼15-nm2 in-plane expansion. Inactivation was retained in whole spheroplast mode, but no adaptation was observed. Similarly, whole spheroplast recordings of MscL (V23T mutant) indicated no adaptation, which was present in excised patches. MscS activities tried in spheroplast-attached mode showed no adaptation when the spheroplasts were intact, but permeabilized spheroplasts showed delayed adaptation, suggesting that the presence of membrane breaks or edges causes adaptation. We interpret this in the framework of the mechanics of the bilayer couple linking adaptation of Channels in excised patches to the relaxation of the inner leaflet that is not in contact with the glass pipette. Relaxation of one leaflet results in asymmetric redistribution of tension in the bilayer that is less favorable for channel opening.

  • gadolinium ions block Mechanosensitive Channels by altering the packing and lateral pressure of anionic lipids
    Biophysical Journal, 2010
    Co-Authors: Yury A Ermakov, Kishore Kamaraju, K Sengupta, Sergei Sukharev
    Abstract:

    Effects of polyvalent ions on the lateral packing of phospholipids have been known for decades, but the physiological consequences have not been systematically studied. Gd3+ is a relatively nonspecific agent that blocks mechano-gated Channels with a variable affinity. In this study, we show that the large Mechanosensitive channel MscL of Escherichia coli is effectively blocked by Gd3+ only when reconstituted with negatively charged phospholipids (e.g., PS). Taking this lead, we studied effects of Gd3+ on monolayers and unilamellar vesicles made of natural brain PS, DMPS, and its mixtures with DMPC. In monolayer experiments, we found that μM Gd3+ present in the subphase leads to ∼8% lateral compaction of brain PS (at 35 mN/m). Gd3+ more strongly shrinks and rigidifies DMPS films causing a spontaneous liquid expanded-to-compact transition to the limiting 40 A2/mol. Pressure-area isotherms of uncharged DMPC were unaffected by Gd3+, and neutralization of DMPS surface by low pH did not produce strong compaction. Upshifts of surface potential isotherms of DMPS monolayers reflected changes in the diffuse double layer due to neutralization of headgroup charges by Gd3+, whereas the increased packing density produced up to a 200 mV change in the interfacial dipole potential. The slopes of surface potential versus reciprocal area predicted that Gd3+ induced a modest (∼18%) increase in the magnitude of the individual lipid dipoles in DMPS. Isothermal titration calorimetry indicated that binding of Gd3+ to DMPS liposomes in the gel state is endothermic, whereas binding to liquid crystalline liposomes produces heat consistent with the isothermal liquid-to-gel phase transition induced by the ion. Both titration curves suggested a Kb of ∼106 M−1. We conclude that anionic phospholipids serve as high-affinity receptors for Gd3+ ions, and the ion-induced compaction generates a lateral pressure increase estimated as tens of mN/m. This pressure can “squeeze” the channel and shift the equilibrium toward the closed state.

Ian R Booth - One of the best experts on this subject based on the ideXlab platform.

  • bacterial Mechanosensitive Channels progress towards an understanding of their roles in cell physiology
    Current Opinion in Microbiology, 2014
    Co-Authors: Ian R Booth
    Abstract:

    Bacterial Mechanosensitive Channels sense the changes in lateral tension in the bilayer of the cytoplasmic membrane generated by rapid water flow into the cell. Two major structural families are found widely distributed across bacteria and archaea: MscL and MscS. Our understanding of the mechanisms of gating has advanced rapidly through genetic analysis, structural biology and electrophysiology. It is only recently that the analysis of the physiological roles of the Channels has kept pace with mechanistic studies. Recent advances have increased our understanding of the role of the Channels in preventing structural perturbation during osmotic transitions and its relationship to water flow across the membrane. It is to these recent developments that this review is dedicated.

  • Mechanosensitive Channels and bacterial cell wall integrity does life end with a bang or a whimper
    Journal of the Royal Society Interface, 2014
    Co-Authors: Marcel Reuter, Susan Shirley Black, Samantha Miller, Nicholas J Hayward, David T F Dryden, Ian R Booth
    Abstract:

    Mechanogated Channels are fundamental components of bacterial cells that enable retention of physical integrity during extreme increases in cell turgor. Optical tweezers combined with microfluidics have been used to study the fate of individual Escherichia coli cells lacking such Channels when subjected to a bursting stress caused by increased turgor. Fluorescence-activated cell sorting and electron microscopy complement these studies. These analyses show that lysis occurs with a high probability, but the precise path differs between individual cells. By monitoring the loss of cytoplasmic green fluorescent protein, we have determined that some cells release this protein but remain phase dark (granular) consistent with the retention of the majority of large proteins. By contrast, most cells suffer cataclysmic wall failure leading to loss of granularity but with the retention of DNA and overall cell shape (protein-depleted ghosts). The time span of these events induced by hypo-osmotic shock varies but is of the order of milliseconds. The data are interpreted in terms of the timing of Mechanosensitive channel gating relative to osmotically induced water influx.

  • the mscs and mscl families of Mechanosensitive Channels act as microbial emergency release valves
    Journal of Bacteriology, 2012
    Co-Authors: Ian R Booth, Paul Blount
    Abstract:

    Single-celled organisms must survive exposure to environmental extremes. Perhaps one of the most variable and potentially life-threatening changes that can occur is that of a rapid and acute decrease in external osmolarity. This easily translates into several atmospheres of additional pressure that can build up within the cell. Without a protective mechanism against such pressures, the cell will lyse. Hence, most microbes appear to possess members of one or both families of bacterial Mechanosensitive Channels, MscS and MscL, which can act as biological emergency release valves that allow cytoplasmic solutes to be jettisoned rapidly from the cell. While this is undoubtedly a function of these proteins, the discovery of the presence of MscS homologues in plant organelles and MscL in fungus and mycoplasma genomes may complicate this simplistic interpretation of the physiology underlying these proteins. Here we compare and contrast these two Mechanosensitive channel families, discuss their potential physiological roles, and review some of the most relevant data that underlie the current models for their structure and function.

  • bacterial Mechanosensitive Channels mscs evolution s solution to creating sensitivity in function
    Annual Review of Biophysics, 2012
    Co-Authors: James H Naismith, Ian R Booth
    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.

  • Mechanosensitive Channels in bacteria signs of closure
    Nature Reviews Microbiology, 2007
    Co-Authors: Ian R Booth, Michelle D Edwards, Susan Shirley Black, Ulrike Schumann, Samantha Miller
    Abstract:

    Bacterial Mechanosensitive Channels are activated by increases in tension in the lipid bilayer of the cytoplasmic membrane, where they transiently create large pores in a controlled manner. Mechanosensitive channel research has benefited from advances in electrophysiology, genomics and molecular genetics as well as from the application of biophysical techniques. Most recently, new analytical methods have been used to complement existing knowledge and generate insights into the molecular interactions that take place between Mechanosensitive channel proteins and the surrounding membrane lipids. This article reviews the latest developments.

Masataka Nakano - One of the best experts on this subject based on the ideXlab platform.

  • involvement of the putative ca 2 permeable Mechanosensitive Channels ntmca1 and ntmca2 in ca 2 uptake ca 2 dependent cell proliferation and mechanical stress induced gene expression in tobacco nicotiana tabacum by 2 cells
    Journal of Plant Research, 2012
    Co-Authors: Takamitsu Kurusu, Masataka Nakano, Takuya Yamanaka, Kazuko Iida, Akiko Takiguchi, Yoko Ogasawara, Teruyuki Hayashi, Shigeru Hanamata, Kazuo Shinozaki
    Abstract:

    To gain insight into the cellular functions of the mid1-complementing activity (MCA) family proteins, encoding putative Ca2+-permeable Mechanosensitive Channels, we isolated two MCA homologs of tobacco (Nicotiana tabacum) BY-2 cells, named NtMCA1 and NtMCA2. NtMCA1 and NtMCA2 partially complemented the lethality and Ca2+ uptake defects of yeast mutants lacking Mechanosensitive Ca2+ channel components. Furthermore, in yeast cells overexpressing NtMCA1 and NtMCA2, the hypo-osmotic shock-induced Ca2+ influx was enhanced. Overexpression of NtMCA1 or NtMCA2 in BY-2 cells enhanced Ca2+ uptake, and significantly alleviated growth inhibition under Ca2+ limitation. NtMCA1-overexpressing BY-2 cells showed higher sensitivity to hypo-osmotic shock than control cells, and induced the expression of the touch-inducible gene, NtERF4. We found that both NtMCA1-GFP and NtMCA2-GFP were localized at the plasma membrane and its interface with the cell wall, Hechtian strands, and at the cell plate and perinuclear vesicles of dividing cells. NtMCA2 transcript levels fluctuated during the cell cycle and were highest at the G1 phase. These results suggest that NtMCA1 and NtMCA2 play roles in Ca2+-dependent cell proliferation and mechanical stress-induced gene expression in BY-2 cells, by regulating the Ca2+ influx through the plasma membrane.

  • plasma membrane protein osmca1 is involved in regulation of hypo osmotic shock induced ca2 influx and modulates generation of reactive oxygen species in cultured rice cells
    BMC Plant Biology, 2012
    Co-Authors: Takamitsu Kurusu, Daisuke Nishikawa, Yukari Yamazaki, Mariko Gotoh, Masataka Nakano, Haruyasu Hamada, Takuya Yamanaka, Kazuko Iida, Yuko Nakagawa
    Abstract:

    Mechanosensing and its downstream responses are speculated to involve sensory complexes containing Ca2+-permeable Mechanosensitive Channels. On recognizing osmotic signals, plant cells initiate activation of a widespread signal transduction network that induces second messengers and triggers inducible defense responses. Characteristic early signaling events include Ca2+ influx, protein phosphorylation and generation of reactive oxygen species (ROS). Pharmacological analyses show Ca2+ influx mediated by Mechanosensitive Ca2+ Channels to influence induction of osmotic signals, including ROS generation. However, molecular bases and regulatory mechanisms for early osmotic signaling events remain poorly elucidated. We here identified and investigated OsMCA1, the sole rice homolog of putative Ca2+-permeable Mechanosensitive Channels in Arabidopsis (MCAs). OsMCA1 was specifically localized at the plasma membrane. A promoter-reporter assay suggested that OsMCA1 mRNA is widely expressed in seed embryos, proximal and apical regions of shoots, and mesophyll cells of leaves and roots in rice. Ca2+ uptake was enhanced in OsMCA1-overexpressing suspension-cultured cells, suggesting that OsMCA1 is involved in Ca2+ influx across the plasma membrane. Hypo-osmotic shock-induced ROS generation mediated by NADPH oxidases was also enhanced in OsMCA1-overexpressing cells. We also generated and characterized OsMCA1-RNAi transgenic plants and cultured cells; OsMCA1-suppressed plants showed retarded growth and shortened rachises, while OsMCA1-suppressed cells carrying Ca2+-sensitive photoprotein aequorin showed partially impaired changes in cytosolic free Ca2+ concentration ([Ca2+]cyt) induced by hypo-osmotic shock and trinitrophenol, an activator of Mechanosensitive Channels. We have identified a sole MCA ortholog in the rice genome and developed both overexpression and suppression lines. Analyses of cultured cells with altered levels of this putative Ca2+-permeable Mechanosensitive channel indicate that OsMCA1 is involved in regulation of plasma membrane Ca2+ influx and ROS generation induced by hypo-osmotic stress in cultured rice cells. These findings shed light on our understanding of mechanical sensing pathways.

Douglas C Rees - One of the best experts on this subject based on the ideXlab platform.

  • Mechanosensitive Channels what can they do and how do they do it
    Structure, 2011
    Co-Authors: Elizabeth S Haswell, Rob Phillips, Douglas C Rees
    Abstract:

    While mechanobiological processes employ diverse mechanisms, at their heart are force-induced perturbations in the structure and dynamics of molecules capable of triggering subsequent events. Among the best characterized force-sensing systems are bacterial Mechanosensitive Channels. These Channels reflect an intimate coupling of protein conformation with the mechanics of the surrounding membrane; the membrane serves as an adaptable sensor that responds to an input of applied force and converts it into an output signal, interpreted for the cell by Mechanosensitive Channels. The cell can exploit this information in a number of ways: ensuring cellular viability in the presence of osmotic stress and perhaps also serving as a signal transducer for membrane tension or other functions. This review focuses on the bacterial Mechanosensitive Channels of large (MscL) and small (MscS) conductance and their eukaryotic homologs, with an emphasis on the outstanding issues surrounding the function and mechanism of this fascinating class of molecules.

  • structures of the prokaryotic Mechanosensitive Channels mscl and mscs
    Current Topics in Membranes, 2007
    Co-Authors: Stefan Steinbacher, Randal B Bass, Pavel Strop, Douglas C Rees
    Abstract:

    Publisher Summary This chapter describes the crystallographic analyses of the Mycobacterium tuberculosis Mechanosensitive Channels of large (MscL) and the Escherichia coli Mechanosensitive Channels of small (MscS). Crystal structures of the M. tuberculosis MscL and E. coli MscS were initially reported at 3.5‐ and 3.9‐ A resolutions, respectively. The basic structural framework of the MscL and MscS transmembrane domains is provided by α ‐helices; each subunit of MscL has two helices for a total of 10, whereas MscS has three helices per subunit for a total of 21. From a structural perspective, MscL and MscS represent fascinating targets as they provide an opportunity to explore the coupling between protein conformation and the membrane environment responsible for channel gating. Tension and pressure sensitive systems, such as MscL and MscS, have the attraction that these environmental properties are energetically coupled to changes in protein area and volume, respectively that may be directly quantitated from structural models.

  • structure and mechanism in prokaryotic Mechanosensitive Channels
    Current Opinion in Structural Biology, 2003
    Co-Authors: Eduardo Perozo, Douglas C Rees
    Abstract:

    Mechanosensitive Channels function as electromechanical switches with the capability to sense the physical state of lipid bilayers. The X-ray crystal structures of MscL and MscS offer a unique opportunity to identify the types of protein motions associated with the opening and closing of these structurally unrelated Channels, while providing the framework to address a mechanism of tension sensing that is defined by channel–lipid interactions. Recent functional, structural and dynamic data offer fresh insights into the molecular basis of gating for these membrane proteins.

  • structure of the mscl homolog from mycobacterium tuberculosis a gated Mechanosensitive ion channel
    Science, 1998
    Co-Authors: Geoffrey Chang, Robert H Spencer, Allen T Lee, Margaret T Barclay, Douglas C Rees
    Abstract:

    Mechanosensitive ion Channels play a critical role in transducing physical stresses at the cell membrane into an electrochemical response. The MscL family of large-conductance Mechanosensitive Channels is widely distributed among prokaryotes and may participate in the regulation of osmotic pressure changes within the cell. In an effort to better understand the structural basis for the function of these Channels, the structure of the MscL homolog fromMycobacterium tuberculosis was determined by x-ray crystallography to 3.5 angstroms resolution. This channel is organized as a homopentamer, with each subunit containing two transmembrane α helices and a third cytoplasmic α helix. From the extracellular side, a water-filled opening approximately 18 angstroms in diameter leads into a pore lined with hydrophilic residues which narrows at the cytoplasmic side to an occluded hydrophobic apex that may act as the channel gate. This structure may serve as a model for other Mechanosensitive Channels, as well as the broader class of pentameric ligand-gated ion Channels exemplified by the nicotinic acetylcholine receptor.