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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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Magarlamov TY, Melnikova DI, Shokur OA, Gorobets EA. Rapid production of tetrodotoxin-like compounds during sporulation in a marine isolate Bacillus sp. 1839. Microbiology (Reading) 2017. [DOI: 10.1134/s0026261717020126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Dipicolinic Acid Release by Germinating Clostridium difficile Spores Occurs through a Mechanosensing Mechanism. mSphere 2016; 1:mSphere00306-16. [PMID: 27981237 PMCID: PMC5156672 DOI: 10.1128/msphere.00306-16] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Accepted: 11/14/2016] [Indexed: 12/18/2022] Open
Abstract
Clostridium difficile is transmitted between hosts in the form of a dormant spore, and germination by C. difficile spores is required to initiate infection, because the toxins that are necessary for disease are not deposited on the spore form. Importantly, the C. difficile spore germination pathway represents a novel pathway for bacterial spore germination. Prior work has shown that the order of events during C. difficile spore germination (cortex degradation and DPA release) is flipped compared to the events during B. subtilis spore germination, a model organism. Here, we further characterize the C. difficile spore germination pathway and summarize our findings indicating that DPA release by germinating C. difficile spores occurs through a mechanosensing mechanism in response to the degradation of the spore cortex. Classically, dormant endospores are defined by their resistance properties, particularly their resistance to heat. Much of the heat resistance is due to the large amount of dipicolinic acid (DPA) stored within the spore core. During spore germination, DPA is released and allows for rehydration of the otherwise-dehydrated core. In Bacillus subtilis, 7 proteins are encoded by the spoVA operon and are important for DPA release. These proteins receive a signal from the activated germinant receptor and release DPA. This DPA activates the cortex lytic enzyme CwlJ, and cortex degradation begins. In Clostridium difficile, spore germination is initiated in response to certain bile acids and amino acids. These bile acids interact with the CspC germinant receptor, which then transfers the signal to the CspB protease. Activated CspB cleaves the cortex lytic enzyme, pro-SleC, to its active form. Subsequently, DPA is released from the core. C. difficile encodes orthologues of spoVAC, spoVAD, and spoVAE. Of these, the B. subtilis SpoVAC protein was shown to be capable of mechanosensing. Because cortex degradation precedes DPA release during C. difficile spore germination (opposite of what occurs in B. subtilis), we hypothesized that cortex degradation would relieve the osmotic constraints placed on the inner spore membrane and permit DPA release. Here, we assayed germination in the presence of osmolytes, and we found that they can delay DPA release from germinating C. difficile spores while still permitting cortex degradation. Together, our results suggest that DPA release during C. difficile spore germination occurs though a mechanosensing mechanism. IMPORTANCEClostridium difficile is transmitted between hosts in the form of a dormant spore, and germination by C. difficile spores is required to initiate infection, because the toxins that are necessary for disease are not deposited on the spore form. Importantly, the C. difficile spore germination pathway represents a novel pathway for bacterial spore germination. Prior work has shown that the order of events during C. difficile spore germination (cortex degradation and DPA release) is flipped compared to the events during B. subtilis spore germination, a model organism. Here, we further characterize the C. difficile spore germination pathway and summarize our findings indicating that DPA release by germinating C. difficile spores occurs through a mechanosensing mechanism in response to the degradation of the spore cortex.
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Spore Cortex Hydrolysis Precedes Dipicolinic Acid Release during Clostridium difficile Spore Germination. J Bacteriol 2015; 197:2276-83. [PMID: 25917906 DOI: 10.1128/jb.02575-14] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 04/21/2015] [Indexed: 12/17/2022] Open
Abstract
UNLABELLED Bacterial spore germination is a process whereby a dormant spore returns to active, vegetative growth, and this process has largely been studied in the model organism Bacillus subtilis. In B. subtilis, the initiation of germinant receptor-mediated spore germination is divided into two genetically separable stages. Stage I is characterized by the release of dipicolinic acid (DPA) from the spore core. Stage II is characterized by cortex degradation, and stage II is activated by the DPA released during stage I. Thus, DPA release precedes cortex hydrolysis during B. subtilis spore germination. Here, we investigated the timing of DPA release and cortex hydrolysis during Clostridium difficile spore germination and found that cortex hydrolysis precedes DPA release. Inactivation of either the bile acid germinant receptor, cspC, or the cortex hydrolase, sleC, prevented both cortex hydrolysis and DPA release. Because both cortex hydrolysis and DPA release during C. difficile spore germination are dependent on the presence of the germinant receptor and the cortex hydrolase, the release of DPA from the core may rely on the osmotic swelling of the core upon cortex hydrolysis. These results have implications for the hypothesized glycine receptor and suggest that the initiation of germinant receptor-mediated C. difficile spore germination proceeds through a novel germination pathway. IMPORTANCE Clostridium difficile infects antibiotic-treated hosts and spreads between hosts as a dormant spore. In a host, spores germinate to the vegetative form that produces the toxins necessary for disease. C. difficile spore germination is stimulated by certain bile acids and glycine. We recently identified the bile acid germinant receptor as the germination-specific, protease-like CspC. CspC is likely cortex localized, where it can transmit the bile acid signal to the cortex hydrolase, SleC. Due to the differences in location of CspC compared to the Bacillus subtilis germinant receptors, we hypothesized that there are fundamental differences in the germination processes between the model organism and C. difficile. We found that C. difficile spore germination proceeds through a novel pathway.
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Booth IR, Miller S, Müller A, Lehtovirta-Morley L. The evolution of bacterial mechanosensitive channels. Cell Calcium 2014; 57:140-50. [PMID: 25591932 DOI: 10.1016/j.ceca.2014.12.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Revised: 12/16/2014] [Accepted: 12/17/2014] [Indexed: 01/17/2023]
Abstract
Mechanosensitive channels are ubiquitous and highly studied. However, the evolution of the bacterial channels remains enigmatic. It can be argued that mechanosensitivity might be a feature of all membrane proteins with some becoming progressively less sensitive to membrane tension over the course of evolution. Bacteria and archaea exhibit two main classes of channels, MscS and MscL. Present day channels suggest that the evolution of MscL may be highly constrained, whereas MscS has undergone elaboration via gene fusion (and potentially gene fission) events to generate a diversity of channel structures. Some of these channel variants are constrained to a small number of genera or species. Some are only found in higher organisms. Only exceptionally have these diverse channels been investigated in any detail. In this review we consider both the processes that might have led to the evolved complexity but also some of the methods exploiting the explosion of genome sequences to understand (and/or track) their distribution. The role of MscS-related channels in calcium-mediated cell biology events is considered.
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Affiliation(s)
- Ian R Booth
- School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK; Division of Biology and Biological Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA.
| | - Samantha Miller
- School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
| | - Axel Müller
- Division of Chemistry and Chemical Engineering, Broad Institute, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA.
| | - Laura Lehtovirta-Morley
- Institute of Biological and Environmental Sciences, Cruikshank Building, University of Aberdeen, St Machar Drive, Aberdeen AB24 3UU, UK.
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Velásquez J, Schuurman-Wolters G, Birkner JP, Abee T, Poolman B. Bacillus subtilisspore protein SpoVAC functions as a mechanosensitive channel. Mol Microbiol 2014; 92:813-23. [DOI: 10.1111/mmi.12591] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/24/2014] [Indexed: 11/27/2022]
Affiliation(s)
- Jeanette Velásquez
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
- TI Food and Nutrition; Wageningen The Netherlands
| | - Gea Schuurman-Wolters
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Jan Peter Birkner
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Tjakko Abee
- TI Food and Nutrition; Wageningen The Netherlands
- Laboratory of Food Microbiology; Wageningen University; Wageningen The Netherlands
| | - Bert Poolman
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
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Setlow P. Summer meeting 2013 - when the sleepers wake: the germination of spores of Bacillus
species. J Appl Microbiol 2013; 115:1251-68. [DOI: 10.1111/jam.12343] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/08/2013] [Accepted: 09/09/2013] [Indexed: 11/27/2022]
Affiliation(s)
- P. Setlow
- Department of Molecular, Microbial and Structural Biology; University of Connecticut Health Center; Farmington CT USA
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Mechanosensitive channels: what can they do and how do they do it? Structure 2012; 19:1356-69. [PMID: 22000509 DOI: 10.1016/j.str.2011.09.005] [Citation(s) in RCA: 240] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2011] [Revised: 09/19/2011] [Accepted: 09/20/2011] [Indexed: 12/16/2022]
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.
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Wahome PG, Cowan AE, Setlow B, Setlow P. Levels and localization of mechanosensitive channel proteins in Bacillus subtilis. Arch Microbiol 2009; 191:403-14. [PMID: 19252899 DOI: 10.1007/s00203-009-0465-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Revised: 01/22/2009] [Accepted: 02/11/2009] [Indexed: 11/30/2022]
Abstract
Log phase Bacillus subtilis cells lacking the mscL gene encoding the mechanosensitive (MS) channel of large conductance are sensitive to an osmotic downshock > or =0.5 M. However, B. subtilis mscL cells develop osmotic downshock resistance in late log and early stationary phase growth that is partially dependent on three likely MS channel proteins of small conductance (MscS), YfkC, YhdY, and YkuT. Bacillus subtilis MS proteins were fused with green fluorescent protein (GFP) at their C termini; at least the MscL-, YfkC-, and YkuT-GFP fusions were functional and overexpression of YkuT-GFP, or YkuT alone abolished log phase mscL cells' osmotic downshock sensitivity. Western blot analysis found high levels of MscL-GFP in early exponential phase cells with levels subsequently decreasing greatly. MscS-GFP proteins were present in exponential phase cells, but again disappeared almost completely in stationary phase cells and these proteins were not detected in spores. Western blot analyses further showed that MS-GFP proteins were associated with the plasma membrane, as expected. Fluorescence microscopy confirmed the localization of MscL-GFP and YhdY-GFP to the plasma membrane, with non-uniform distribution of these proteins along this membrane consistent with but by no means proving that these proteins are present in a helical array.
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Affiliation(s)
- Paul G Wahome
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-3305, USA
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Kouwen TRHM, Antelmann H, van der Ploeg R, Denham EL, Hecker M, van Dijl JM. MscL of Bacillus subtilis prevents selective release of cytoplasmic proteins in a hypotonic environment. Proteomics 2009; 9:1033-43. [DOI: 10.1002/pmic.200800483] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Release of small molecules during germination of spores of Bacillus Species. J Bacteriol 2008; 190:4759-63. [PMID: 18469112 DOI: 10.1128/jb.00399-08] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Free amino acids, dipicolinic acid, and unidentified small molecules were released early in Bacillus spore germination before hydrolysis of the peptidoglycan cortex, but adenine nucleotides and 3-phosphoglycerate were not. These results indicate that early in germination there is a major selective change in the permeability of the spore's inner membrane.
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Responses of Bacillus subtilis to hypotonic challenges: physiological contributions of mechanosensitive channels to cellular survival. Appl Environ Microbiol 2008; 74:2454-60. [PMID: 18310427 DOI: 10.1128/aem.01573-07] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mechanosensitive channels are thought to function as safety valves for the release of cytoplasmic solutes from cells that have to manage a rapid transition from high- to low-osmolarity environments. Subsequent to an osmotic down-shock of cells grown at high osmolarity, Bacillus subtilis rapidly releases the previously accumulated compatible solute glycine betaine in accordance with the degree of the osmotic downshift. Database searches suggest that B. subtilis possesses one copy of a gene for a mechanosensitive channel of large conductance (mscL) and three copies of genes encoding proteins that putatively form mechanosensitive channels of small conductance (yhdY, yfkC, and ykuT). Detailed mutational analysis of all potential channel-forming genes revealed that a quadruple mutant (mscL yhdY yfkC ykuT) has no growth disadvantage in high-osmolarity media in comparison to the wild type. Osmotic down-shock experiments demonstrated that the MscL channel is the principal solute release system of B. subtilis, and strains with a gene disruption in mscL exhibited a severe survival defect upon an osmotic down-shock. We also detected a minor contribution of the SigB-controlled putative MscS-type channel-forming protein YkuT to cellular survival in an mscL mutant. Taken together, our data revealed that mechanosensitive channels of both the MscL and MscS types play pivotal roles in managing the transition of B. subtilis from hyper- to hypo-osmotic environments.
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Vepachedu VR, Hirneisen K, Hoover DG, Setlow P. Studies of the release of small molecules during pressure germination of spores of Bacillus subtilis. Lett Appl Microbiol 2007; 45:342-8. [PMID: 17718850 DOI: 10.1111/j.1472-765x.2007.02204.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AIMS To measure rates of release of small molecules during pressure germination of Bacillus subtilis spores, and the role of SpoVA proteins in dipicolinic acid (DPA) release. METHODS AND RESULTS Rates of DPA release during B. subtilis spore germination with pressures of 150 or 500 megaPascals were much higher in spores with elevated levels of SpoVA proteins, and spores with a temperature-sensitive mutation in the spoVA operon were temperature-sensitive in DPA release during pressure germination. Spores also released arginine and glutamic acid, but not AMP, during pressure germination. CONCLUSIONS Pressure germination of B. subtilis spores causes release of many small molecules including DPA. SpoVA proteins are involved in the release of DPA, perhaps because SpoVA proteins are a component of a DPA channel in the spore's inner membrane. SIGNIFICANCE AND IMPACT OF THE STUDY This work provides new insight into the mechanism of pressure germination of spores of Bacillus species, a process that has significant potential for usage in the food industry.
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Affiliation(s)
- V R Vepachedu
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, CT 06032-3305, USA
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Wahome PG, Setlow P. Growth, osmotic downshock resistance and differentiation of Bacillus subtilis strains lacking mechanosensitive channels. Arch Microbiol 2007; 189:49-58. [PMID: 17665170 DOI: 10.1007/s00203-007-0292-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2007] [Revised: 06/08/2007] [Accepted: 07/12/2007] [Indexed: 10/23/2022]
Abstract
Previous work has shown that the mechanosensitive (MS) channel of large conductance (MscL) is essential for preventing lysis of Bacillus subtilis log phase cells upon a rapid, severe osmotic downshock. Growing cells of B. subtilis strains lacking MscL and one or more putative MS channel proteins of small conductance (YhdY, YkuT and YfkC) showed even higher sensitivity to an osmotic downshock. The effect was greatest for a strain lacking MscL and YkuT, and a strain lacking all four MS channel proteins had a similar phenotype. These defects were complemented by expression of either MscL or YkuT in trans. All MS channel mutant strains ultimately became resistant to osmotic downshock in stationary phase but at varying times, with mscL ykuT strains taking the longest time to become resistant. Expression of beta-galactosidase from gene fusions to lacZ showed modest expression of ykuT and lower levels of expression of yhdY and yfkC when strains were grown in medium containing high salt. Sporulation of all MS channel mutant strains was normal, and the mutant spores germinated normally with L-alanine or dodecylamine.
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Affiliation(s)
- Paul G Wahome
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-3305, USA
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