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Contribution of mechanosensitive channels to osmoadaptation and ectoine excretion in Halomonas elongata. Extremophiles 2020; 24:421-432. [PMID: 32266565 PMCID: PMC7174268 DOI: 10.1007/s00792-020-01168-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 03/24/2020] [Indexed: 12/05/2022]
Abstract
For osmoadaptation the halophilic bacterium Halomonas elongata synthesizes as its main compatible solute the aspartate derivative ectoine. H. elongata does not rely entirely on synthesis but can accumulate ectoine by uptake from the surrounding environment with the help of the osmoregulated transporter TeaABC. Disruption of the TeaABC-mediated ectoine uptake creates a strain that is constantly losing ectoine to the medium. However, the efflux mechanism of ectoine in H. elongata is not yet understood. H. elongata possesses four genes encoding mechanosensitive channels all of which belong to the small conductance type (MscS). Analysis by qRT-PCR revealed a reduction in transcription of the mscS genes with increasing salinity. The response of H. elongata to hypo- and hyperosmotic shock never resulted in up-regulation but rather in down-regulation of mscS transcription. Deletion of all four mscS genes created a mutant that was unable to cope with hypoosmotic shock. However, the knockout mutant grew significantly faster than the wildtype at high salinity of 2 M NaCl, and most importantly, still exported 80% of the ectoine compared to the wildtype. We thus conclude that a yet unknown system, which is independent of mechanosensitive channels, is the major export route for ectoine in H. elongata.
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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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Gao S, Zhang L, Li D, Liu S, Li X. Comparison of ectoine synthesis regulation in secreting and non-secreting strains of Halomonas. ANN MICROBIOL 2013. [DOI: 10.1007/s13213-013-0779-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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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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Booth IR, Edwards MD, Black S, Schumann U, Bartlett W, Rasmussen T, Rasmussen A, Miller S. Physiological analysis of bacterial mechanosensitive channels. Methods Enzymol 2007; 428:47-61. [PMID: 17875411 DOI: 10.1016/s0076-6879(07)28003-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Bacterial mechanosensitive (MS) channels play a significant role in protecting cells against hypoosmotic shock. Bacteria that have been diluted from high osmolarity medium into dilute solution are required to cope with sudden water influx associated with an osmotic imbalance equivalent to 10 to 14 atm. The cell wall is only poorly expansive and the cytoplasmic membrane even less so. Thus, swelling is not an option and the cell must rapidly eject solutes to diminish the osmotic gradient and thereby preserve structural integrity. This chapter describes cellular assays of MS channel function and their interpretation.
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Affiliation(s)
- Ian R Booth
- School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, United Kingdom
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Structure–Function Relations of MscS. CURRENT TOPICS IN MEMBRANES 2007. [DOI: 10.1016/s1063-5823(06)58010-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
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Choquet G, Jehan N, Pissavin C, Blanco C, Jebbar M. OusB, a broad-specificity ABC-type transporter from Erwinia chrysanthemi, mediates uptake of glycine betaine and choline with a high affinity. Appl Environ Microbiol 2005; 71:3389-98. [PMID: 16000740 PMCID: PMC1169054 DOI: 10.1128/aem.71.7.3389-3398.2005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability of Erwinia chrysanthemi to cope with environments of elevated osmolality is due in part to the transport and accumulation of osmoprotectants. In this study we have identified a high-affinity glycine betaine and choline transport system in E. chrysanthemi. By using a pool of Tn5-B21 ousA mutants, we isolated a mutant that could grow in the presence of a toxic analogue of glycine betaine (benzyl-glycine betaine) at high osmolalities. This mutant was impaired in its ability to transport all effective osmoprotectants in E. chrysanthemi. The DNA sequence of the regions flanking the transposon insertion site revealed three chromosomal genes (ousVWX) that encode components of an ABC-type transporter (OusB): OusV (ATPase), OusW (permease), and OusX (periplasmic binding protein). The OusB components showed a significant degree of sequence identity to components of ProU from Salmonella enterica serovar Typhimurium and Escherichia coli. OusB was found to restore the uptake of glycine betaine and choline through functional complementation of an E. coli mutant defective in both ProU and ProP osmoprotectant uptake systems. Competition experiments demonstrated that choline, dimethylsulfoniacetate, dimethylsulfoniopropionate, and ectoine were effective competitors for OusB-mediated betaine transport but that carnitine, pipecolate, and proline were not effective. In addition, the analysis of single and double mutants showed that OusA and OusB were the only osmoprotectant transporters operating in E. chrysanthemi.
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Affiliation(s)
- Gwénaëlle Choquet
- Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Ave. du Général Leclerc, 35042 Rennes, France
| | - Nathalie Jehan
- Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Ave. du Général Leclerc, 35042 Rennes, France
| | - Christine Pissavin
- Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Ave. du Général Leclerc, 35042 Rennes, France
| | - Carlos Blanco
- Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Ave. du Général Leclerc, 35042 Rennes, France
| | - Mohamed Jebbar
- Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Ave. du Général Leclerc, 35042 Rennes, France
- Corresponding author. Mailing address: Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Av. du Général Leclerc, 35042 Rennes, France. Phone: (33) 2-23-23-68-52. Fax: (33) 2-23-23-67-75. E-mail:
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Touzé T, Goude R, Georgeault S, Blanco C, Bonnassie S. Erwinia chrysanthemi O antigen is required for betaine osmoprotection in high-salt media. J Bacteriol 2004; 186:5547-50. [PMID: 15292161 PMCID: PMC490874 DOI: 10.1128/jb.186.16.5547-5550.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cellular components necessary for osmoprotection are poorly known. In this study we show that O antigen is specifically required for the effectiveness of betaines as osmoprotectants for Erwinia chrysanthemi in saline media. The phenotype is correlated with the inability of rfb mutant strains to maintain a high accumulation level of betaines in hypersaline media.
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Affiliation(s)
- Thierry Touzé
- Osmorégulation chez les bactéries, CNRS UMR 6026, Campus de Beaulieu, Université de Rennes I, 35042 Rennes, France
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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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Miller S, Bartlett W, Chandrasekaran S, Simpson S, Edwards M, Booth IR. Domain organization of the MscS mechanosensitive channel of Escherichia coli. EMBO J 2003; 22:36-46. [PMID: 12505982 PMCID: PMC140058 DOI: 10.1093/emboj/cdg011] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The major structural features of the Escherichia coli MscS mechanosensitive channel protein have been explored using alkaline phosphatase (PhoA) fusions, precise deletions and site-directed mutations. PhoA protein fusion data, combined with the positive-inside rule, strongly support a model in which MscS crosses the membrane three times, adopting an N(out)-C(in) configuration. Deletion data suggest that the C-terminal domain of the protein is essential for the stability of the MscS channel, whereas the protein will tolerate small deletions at the N-terminus. Four mutants that exhibit either gain-of-function (GOF) or loss-of-function have been identified: a double mutation I48D/S49P inactivates MscS, whereas the MscS mutants T93R, A102P and L109S cause a strong GOF phenotype. The similarity of MscS to the last two domains of MscK (formerly KefA) is reinforced by the demonstration that expression of a truncated MscK protein can substitute for MscL and MscS in downshock survival assays. The data derived from studies of the organization, conservation and the influence of mutations provide significant insights into the structure of the MscS channel.
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Affiliation(s)
| | | | - Subramanian Chandrasekaran
- Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Aberdeen AB25 2ZD, UK
Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
| | | | | | - Ian R. Booth
- Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Aberdeen AB25 2ZD, UK
Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
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Li Y, Moe PC, Chandrasekaran S, Booth IR, Blount P. Ionic regulation of MscK, a mechanosensitive channel from Escherichia coli. EMBO J 2002; 21:5323-30. [PMID: 12374733 PMCID: PMC129069 DOI: 10.1093/emboj/cdf537] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2002] [Revised: 08/19/2002] [Accepted: 08/21/2002] [Indexed: 11/13/2022] Open
Abstract
Three gene products that form independent mechanosensitive channel activities have been identified in Escherichia coli. Two of these, MscL and MscS, play a vital role in allowing the cell to survive acute hypotonic stress. Much less is known of the third protein, MscK (KefA). Here, we characterize the MscK channel activity and compare it with the activity of its structural and functional homologue, MscS. While both show a slight anionic preference, MscK appears to be more sensitive to membrane tension. In addition, MscK, but not MscS activity appears to be regulated by external ionic environment, requiring not only membrane tension but also high concentrations of external K(+), NH(4)(+), Rb(+) or Cs(+) to gate; no activity is observed with Na(+), Li(+) or N-methyl-D-glucamine (NMDG). An MscK gain-of-function mutant gates spontaneously in the presence of K(+) or similar ions, and will gate in the presence of Na(+), Li(+) and NMDG, but only when stimulated by membrane tension. Increased sensitivity and the highly regulated nature of MscK suggest a more specialized physiological role than other bacterial mechanosensitive channels.
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Affiliation(s)
- Yuezhou Li
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA and Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
| | - Paul C. Moe
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA and Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
| | - Subramanian Chandrasekaran
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA and Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
| | - Ian R. Booth
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA and Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
| | - Paul Blount
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA and Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK Present address: Division of Biochemistry, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK Corresponding author e-mail:
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Okada K, Moe PC, Blount P. Functional design of bacterial mechanosensitive channels. Comparisons and contrasts illuminated by random mutagenesis. J Biol Chem 2002; 277:27682-8. [PMID: 12015316 DOI: 10.1074/jbc.m202497200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MscS and MscL are mechanosensitive channels found in bacterial plasma membranes that open large pores in response to membrane tension. These channels function to alleviate excess cell turgor invoked by rapid osmotic downshock. Although much is known of the structure and molecular mechanisms underlying MscL, genes correlating with MscS activity have only recently been identified. Previously, it was shown that eliminating the expression of Escherichia coli yggB removed a major portion of MscS activity. YggB is distinct from MscL by having no obvious structural similarity. Here we have reconstituted purified YggB in proteoliposomes and have successfully detected MscS channel activity, confirming that purified YggB protein encodes MscS activity. Additionally, to define functional regions of the channel protein, we have randomly mutagenized the structural gene and isolated a mutant that evokes a gain-of-function phenotype. Physiological experiments demonstrate that the mutated channel allows leakage of solutes from the cell, suggesting inappropriate channel opening. Interestingly, this mutation is analogous in position and character to mutations yielding a similar phenotype in MscL. Hence, although MscS and MscL mechanosensitive channels are structurally quite distinct, there may be analogies in their gating mechanisms.
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Affiliation(s)
- Kuniyuki Okada
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9040, USA
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Grammann K, Volke A, Kunte HJ. New type of osmoregulated solute transporter identified in halophilic members of the bacteria domain: TRAP transporter TeaABC mediates uptake of ectoine and hydroxyectoine in Halomonas elongata DSM 2581(T). J Bacteriol 2002; 184:3078-85. [PMID: 12003950 PMCID: PMC135061 DOI: 10.1128/jb.184.11.3078-3085.2002] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The halophilic bacterium Halomonas elongata synthesizes as its main compatible solute the aspartate derivative ectoine. We constructed a deletion mutant of H. elongata, KB1, defective in ectoine synthesis and tolerating elevated salt concentrations only in the presence of external compatible solutes. The dependency of KB1 on solute uptake for growth in high-salt medium was exploited to select insertion mutants unable to accumulate external solutes via osmoregulated transporters. One insertion mutant out of 7,200 failed to accumulate the osmoprotectants ectoine and hydroxyectoine. Genetic analysis of the insertion site proved that the mutation affected an open reading frame (ORF) of 1,281 bp (teaC). The nucleotide sequence upstream of teaC was determined, and two further ORFs of 603 bp (teaB) and 1,023 bp (teaA) were identified. Deletion of teaA and teaB proved that all three genes are mandatory for ectoine uptake. Sequence comparison showed significant identity of TeaA, TeaB, and TeaC to the transport proteins of the recently identified tripartite ATP-independent periplasmic transporter family (TRAP-T). The affinity of the cells for ectoines was determined (K(s) = 21.7 microM), suggesting that the transporter TeaABC exhibits high affinity for ectoines. An elevation of the external osmolarity resulted in a strong increase in ectoine uptake via TeaABC, demonstrating that this transporter is osmoregulated. Deletion of teaC and teaBC in the wild-type strain led to mutants which excreted significant amounts of ectoine into the medium when cultivated at high salt concentrations. Therefore, the physiological role of TeaABC may be primarily to recover ectoine leaking through the cytoplasmic membrane.
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Affiliation(s)
- Katrin Grammann
- Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität, D-53115 Bonn, Germany
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