1
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Huang Y, Soliakov A, Le Brun AP, Macdonald C, Johnson CL, Solovyova AS, Waller H, Moore GR, Lakey JH. Helix N-Cap Residues Drive the Acid Unfolding That Is Essential in the Action of the Toxin Colicin A. Biochemistry 2019; 58:4882-4892. [PMID: 31686499 PMCID: PMC6899464 DOI: 10.1021/acs.biochem.9b00705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 10/31/2019] [Indexed: 11/28/2022]
Abstract
Numerous bacterial toxins and other virulence factors use low pH as a trigger to convert from water-soluble to membrane-inserted states. In the case of colicins, the pore-forming domain of colicin A (ColA-P) has been shown both to undergo a clear acidic unfolding transition and to require acidic lipids in the cytoplasmic membrane, whereas its close homologue colicin N shows neither behavior. Compared to that of ColN-P, the ColA-P primary structure reveals the replacement of several uncharged residues with aspartyl residues, which upon replacement with alanine induce an unfolded state at neutral pH. Here we investigate ColA-P's structural requirement for these critical aspartyl residues that are largely situated at the N-termini of α helices. As previously shown in model peptides, the charged carboxylate side chain can act as a stabilizing helix N-Cap group by interacting with free amide hydrogen bond donors. Because this could explain ColA-P destabilization when the aspartyl residues are protonated or replaced with alanyl residues, we test the hypothesis by inserting asparagine, glutamine, and glutamate residues at these sites. We combine urea (fluorescence and circular dichroism) and thermal (circular dichroism and differential scanning calorimetry) denaturation experiments with 1H-15N heteronuclear single-quantum coherence nuclear magnetic resonance spectroscopy of ColA-P at different pH values to provide a comprehensive description of the unfolding process and confirm the N-Cap hypothesis. Furthermore, we reveal that, in urea, the single domain ColA-P unfolds in two steps; low pH destabilizes the first step and stabilizes the second.
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Affiliation(s)
- Yan Huang
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
- College
of Chemistry and Molecular Sciences, Wuhan
University, Wuhan 430072, People’s Republic of China
| | - Andrei Soliakov
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
| | - Anton P. Le Brun
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
- Australian
Centre for Neutron Scattering, Australian
Nuclear Science and Technology Organisation, Kirrawee DC, NSW 2232, Australia
| | - Colin Macdonald
- Department
of Chemistry Centre for Structural & Molecular Biology, School
of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Christopher L. Johnson
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
| | - Alexandra S. Solovyova
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
| | - Helen Waller
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
| | - Geoffrey R. Moore
- Department
of Chemistry Centre for Structural & Molecular Biology, School
of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Jeremy H. Lakey
- Institute
for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne NE2 4HH, U.K.
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2
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Resolving the 3D spatial orientation of helix I in the closed state of the colicin E1 channel domain by FRET. Insights into the integration mechanism. Arch Biochem Biophys 2016; 608:52-73. [DOI: 10.1016/j.abb.2016.08.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 07/27/2016] [Accepted: 08/08/2016] [Indexed: 11/13/2022]
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3
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Pulagam LP, Steinhoff HJ. Acidic pH-Induced Membrane Insertion of Colicin A into E. coli Natural Lipids Probed by Site-Directed Spin Labeling. J Mol Biol 2013; 425:1782-94. [DOI: 10.1016/j.jmb.2013.01.037] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2012] [Revised: 01/30/2013] [Accepted: 01/31/2013] [Indexed: 10/27/2022]
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4
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Ho D, Lugo MR, Merrill AR. Harmonic analysis of the fluorescence response of bimane adducts of colicin E1 at helices 6, 7, and 10. J Biol Chem 2012; 288:5136-48. [PMID: 23264635 DOI: 10.1074/jbc.m112.436303] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pre-channel state of helices 6, 7, and 10 (Val(447)-Gly(475) and Ile(508)-Ile(522)) of colicin E1 was investigated by a site-directed fluorescence labeling technique. A total of 44 cysteine variants were purified and covalently labeled with monobromobimane fluorescent probe. A variety of fluorescence properties of the bimane fluorophore were measured for both the soluble and membrane-bound states of the channel peptide, including the fluorescence emission maximum, fluorescence anisotropy, and membrane bilayer penetration depth. Using site-directed fluorescence labeling combined with our novel helical periodicity analysis method, the data revealed that helices 6, 7, and 10 are separate amphipathic α-helices with a calculated periodicity of T = 3.34 ± 0.08 for helix 6, T = 3.56 ± 0.03 for helix 7, and T = 2.99 ± 0.12 for helix 10 in the soluble state. In the membrane-bound state, the helical periodicity was determined to be T = 3.00 ± 0.15 for helix 6, T = 3.68 ± 0.03 for helix 7, and T = 3.47 ± 0.04 for helix 10. Dual fluorescence quencher analysis showed that both helices 6 and 7 adopt a tilted topology that correlates well with the analysis based on the fluorescence anisotropy profile. These data provide further support for the umbrella model of the colicin E1 channel domain.
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Affiliation(s)
- Derek Ho
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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5
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Honigmann A, Pulagam LP, Sippach M, Bartsch P, Steinhoff HJ, Wagner R. A high resolution electro-optical approach for investigating transition of soluble proteins to integral membrane proteins probed by colicin A. Biochem Biophys Res Commun 2012; 427:385-91. [PMID: 23000162 DOI: 10.1016/j.bbrc.2012.09.069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Accepted: 09/12/2012] [Indexed: 02/02/2023]
Abstract
The transition from water soluble state to an integral membrane protein state is a crucial step in the formation of the active form of many pore-forming or receptor proteins. Albeit this, high resolution techniques which allow assay of protein membrane binding and concomitant development of the final active form in the membrane await further development. Here, we describe a horizontal artificial bilayers setup allowing for simultaneous electrical and optical measurements at a single molecule level. We use the membrane binding and subsequent channel formation of colicin A (ColA) a water soluble bacteriocin secreted by some strains of Escherichia coli to demonstrate the potential of the combined electro-optical technique. Our results expand the knowledge on ColA molecular details which show that active ColA is monomeric; membrane binding is pH but not membrane-potential (Δϕ) dependent. ColA is at Δϕ=0 permeable for molecules ≥1 nm. Although ColA exhibits low ion conductance it facilitates permeation of large molecules. Our electro-optical recordings reveal ColA monomeric state and the chimeric character of its pore.
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Affiliation(s)
- Alf Honigmann
- Universität Osnabrück, FB Biologie/Chemie, Barbara Str. 13, 49076 Osnabrück, Germany
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6
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Romano FB, Rossi KC, Sava CG, Holzenburg A, Clerico EM, Heuck AP. Efficient isolation of Pseudomonas aeruginosa type III secretion translocators and assembly of heteromeric transmembrane pores in model membranes. Biochemistry 2011; 50:7117-31. [PMID: 21770428 PMCID: PMC3171962 DOI: 10.1021/bi200905x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Translocation of bacterial toxins or effectors into host cells using the type III secretion (T3S) system is a conserved mechanism shared by many Gram-negative pathogens. Pseudomonas aeruginosa injects different proteins across the plasma membrane of target cells, altering the normal metabolism of the host. Protein translocation presumably occurs through a proteinaceous transmembrane pore formed by two T3S secreted protein translocators, PopB and PopD. Unfolded translocators are secreted through the T3S needle prior to insertion into the target membrane. Purified PopB and PopD form pores in model membranes. However, their tendency to form heterogeneous aggregates in solution had hampered the analysis of how these proteins undergo the transition from a denatured state to a membrane-inserted state. Translocators were purified as stable complexes with the cognate chaperone PcrH and isolated from the chaperone using 6 M urea. We report here the assembly of stable transmembrane pores by dilution of urea-denatured translocators in the presence of membranes. PopB and PopD spontaneously bound liposomes containing anionic phospholipids and cholesterol in a pH-dependent manner as observed by two independent assays, time-resolved Förster resonance energy transfer and sucrose-step gradient ultracentrifugation. Using Bodipy-labeled proteins, we found that PopB interacts with PopD on the membrane surface as determined by excitation energy migration and fluorescence quenching. Stable transmembrane pores are more efficiently assembled at pH <5.0, suggesting that acidic residues might be involved in the initial membrane binding and/or insertion. Altogether, the experimental setup described here represents an efficient method for the reconstitution and analysis of membrane-inserted translocators.
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Affiliation(s)
- Fabian B. Romano
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
- Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Kyle C. Rossi
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Christos G. Sava
- Microscopy and Imaging Center, Texas A&M University, College Station, TX 77843, USA
| | - Andreas Holzenburg
- Microscopy and Imaging Center, Texas A&M University, College Station, TX 77843, USA
- Department of Biology, Texas A&M University, College Station, TX 77843, USA
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA
| | - Eugenia M. Clerico
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Alejandro P. Heuck
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
- Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, MA 01003, USA
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7
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Membrane topology of the colicin E1 channel using genetically encoded fluorescence. Biochemistry 2011; 50:4830-42. [PMID: 21528912 DOI: 10.1021/bi101934e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The membrane topology of the colicin E1 channel domain was studied by fluorescence resonance energy transfer (FRET). The FRET involved a genetically encoded fluorescent amino acid (coumarin) as the donor and a selectively labeled cysteine residue tethered with DABMI (4-(dimethylamino)phenylazophenyl-4'-maleimide) as the FRET acceptor. The fluorescent coumarin residue was incorporated into the protein via an orthogonal tRNA/aminoacyl-tRNA synthetase pair that allowed selective incorporation into any site within the colicin channel domain. Each variant harbored a stop (TAG) mutation for coumarin incorporation and a cysteine (TGT) mutation for DABMI attachment. Six interhelical distances within helices 1-6 were determined using FRET analysis for both the soluble and membrane-bound states. The FRET data showed large changes in the interhelical distances among helices 3-6 upon membrane association providing new insight into the membrane-bound structure of the channel domain. In general, the coumarin-DABMI FRET interhelical efficiencies decreased upon membrane binding, building upon the umbrella model for the colicin channel. A tentative model for the closed state of the channel domain was developed based on current and previously published FRET data. The model suggests circular arrangement of helices 1-7 in a clockwise direction from the extracellular side and membrane interfacial association of helices 1, 6, 7, and 10 around the central transmembrane hairpin formed by helices 8 and 9.
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8
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Yezid H, Konate K, Debaisieux S, Bonhoure A, Beaumelle B. Mechanism for HIV-1 Tat insertion into the endosome membrane. J Biol Chem 2009; 284:22736-46. [PMID: 19549783 DOI: 10.1074/jbc.m109.023705] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The human immunodeficiency virus, type 1, transactivating protein Tat is a small protein that is strictly required for viral transcription and multiplication within infected cells. The infected cells actively secrete Tat using an unconventional secretion pathway. Extracellular Tat can affect different cell types and induce severe cell dysfunctions ranging from cell activation to cell death. To elicit most cell responses, Tat needs to reach the cell cytosol. To this end, Tat is endocytosed, and low endosomal pH will then trigger Tat translocation to the cytosol. Although this translocation step is critical for Tat cytosolic delivery, how Tat could interact with the endosome membrane is unknown, and the key residues involved in this interaction require identification. We found that, upon acidification below pH 6.0 (i.e. within the endosomal pH range), Tat inserts into model membranes such as monolayers or lipid vesicles. This insertion process relies on Tat single Trp, Trp-11, which is not needed for transactivation and could be replaced by another aromatic residue for membrane insertion. Nevertheless, Trp-11 is strictly required for translocation. Tat conformational changes induced by low pH involve a sensor made of its first acidic residue (Glu/Asp-2) and the end of its basic domain (residues 55-57). Mutation of one of these elements results in membrane insertion above pH 6.5. Tat basic domain is also required for efficient Tat endocytosis and membrane insertion. Together with the strict conservation of Tat Trp among different virus isolates, our results point to an important role for Tat-membrane interaction in the multiplication of human immunodeficiency virus type 1.
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Affiliation(s)
- Hocine Yezid
- Centre d'Etudes d'Agents Pathogènes et Biotechnologies pour la Santé, UMR 5236 CNRS, Université Montpellier II, 34095 Montpellier, France
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9
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Ho D, Merrill AR. Evidence for the Amphipathic Nature and Tilted Topology of Helices 4 and 5 in the Closed State of the Colicin E1 Channel. Biochemistry 2009; 48:1369-80. [DOI: 10.1021/bi801906v] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Derek Ho
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - A. Rod Merrill
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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10
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Abstract
The bacterial potassium channel KcsA is gated by high concentrations of intracellular protons, allowing the channel to open at pH < 5.5. Despite prior attempts to determine the mechanism responsible for pH gating, the proton sensor has remained elusive. We have constructed a KcsA channel mutant that remains open up to pH 9.0 by replacing key ionizable residues from the N and C termini of KcsA with residues mimicking their protonated counterparts with respect to charge. A series of individual and combined mutations were investigated by using single-channel recordings in lipid bilayers. We propose that these residues are the proton-binding sites and at neutral pH they form a complex network of inter- and intrasubunit salt bridges and hydrogen bonds near the bundle crossing that greatly stabilize the closed state. In our model, these residues change their ionization state at acidic pH, thereby disrupting this network, modifying the electrostatic landscape near the channel gate, and favoring channel opening.
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11
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Ciardiello MA, Meleleo D, Saviano G, Crescenzo R, Carratore V, Camardella L, Gallucci E, Micelli S, Tancredi T, Picone D, Tamburrini M. Kissper, a kiwi fruit peptide with channel-like activity: Structural and functional features. J Pept Sci 2008; 14:742-54. [PMID: 18186145 DOI: 10.1002/psc.992] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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12
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Wei Z, White D, Wang J, Musse AA, Merrill AR. Tilted, extended, and lying in wait: the membrane-bound topology of residues Lys-381-Ser-405 of the colicin E1 channel domain. Biochemistry 2007; 46:6074-85. [PMID: 17455912 DOI: 10.1021/bi700317k] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The membrane-bound closed state (zero potential) of the helix 3 segment (Lys-381-Ser-405) of the colicin E1 channel domain was investigated by site-directed fluorescence labeling using a bimane probe tethered to a single cysteine residue of each mutant protein. A number of fluorescence properties of the tethered bimane probe were measured for the soluble channel mutant proteins as well as for the membrane-bound proteins. A new method called helical periodicity surface analysis was employed to fit the fluorescence data to a harmonic wave function using four different statistical methods. The fit of the various data sets to a harmonic wave function indicated that the periodicity of helix 3 in the membrane-bound state is typical for an amphipathic alpha helix (3.7-4.0 residues per turn and an angular frequency between 90 and 97 degrees). Notably, upon membrane binding, helix 3 elongates from 15 residues (soluble structure) to 20 residues by a three- and two-residue extension at the N- and C-termini of the helix, respectively. Dual quencher analysis also revealed that helix 3 is appressed to the surface of the membrane with its N-terminus more deeply buried within the interfacial region of the bilayer than its C-terminus. Finally, contrary to a previous report, our data show that helices 3 and 4 remain separate and independent helices upon membrane association in the absence of a membrane potential.
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Affiliation(s)
- Zhikui Wei
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
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13
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Srivastava J, Barber DL, Jacobson MP. Intracellular pH sensors: design principles and functional significance. Physiology (Bethesda) 2007; 22:30-9. [PMID: 17289928 DOI: 10.1152/physiol.00035.2006] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Changes in intracellular pH regulate many cell behaviors, including proliferation, migration, and transformation. However, our understanding of how physiological changes in pH affect protein conformations and macromolecular assemblies is limited. We present design principles, current modeling predictions, and examples of pH sensors or proteins that have activities or ligand-binding affinities that are regulated by changes in intracellular pH.
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Affiliation(s)
- Jyoti Srivastava
- Department of Cell and Tissue Biology, Unicversity of California-San Francisco, San Francisco, CA, USA
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14
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Lascu I. Nm23-H1/NDP kinase folding intermediates and cancer: a hypothesis. J Bioenerg Biomembr 2006; 38:265-8. [PMID: 16944300 DOI: 10.1007/s10863-006-9042-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2005] [Accepted: 04/07/2006] [Indexed: 11/28/2022]
Abstract
The Nm23-H1/nucleoside diphosphate (NDP) kinase A is a metastasis suppressor, besides its enzymatic activity. The mutant S120G has been found in high-grade neuroblastomas. The mutant protein, once denatured in urea, is unable to refold in vitro. A size-exclusion chromatography analysis of the folding/association pathway showed that recombinant wild-type and S120G mutant human Nm23-H1/NDP kinase A unfold and refold passing through a molten globule state while typical hexameric NDP kinases unfold without dissociated species and refold through a native monomeric intermediate. A survey of the recent literature showed that several proteins involved in cancer, and their mutants, are marginally stable, like the wild-type Nm23-H1/NDP kinase A, or are misfolded, like its S120G mutant. We therefore suggest that the low thermodynamic stability and the folding intermediate of the Nm23-H1/NDP kinase A may be necessary for its regulatory properties.
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Affiliation(s)
- Ioan Lascu
- Institut de Biochimie et Génétique Cellulaires, UMR 5095 University Victor Segalen Bordeaux2 and CNRS, 1, rue Camille Saint-Saëns, 33077, Bordeaux Cedex, France.
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15
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Wang J, Rosconi MP, London E. Topography of the hydrophilic helices of membrane-inserted diphtheria toxin T domain: TH1-TH3 as a hydrophilic tether. Biochemistry 2006; 45:8124-34. [PMID: 16800637 PMCID: PMC2519890 DOI: 10.1021/bi060587f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
After low pH-triggered membrane insertion, the T domain of diphtheria toxin helps translocate the catalytic domain of the toxin across membranes. In this study, the hydrophilic N-terminal helices of the T domain (TH1-TH3) were studied. The conformation triggered by exposure to low pH and changes in topography upon membrane insertion were studied. These experiments involved bimane or BODIPY labeling of single Cys introduced at various positions, followed by the measurement of bimane emission wavelength, bimane exposure to fluorescence quenchers, and antibody binding to BODIPY groups. Upon exposure of the T domain in solution to low pH, it was found that the hydrophobic face of TH1, which is buried in the native state at neutral pH, became exposed to solution. When the T domain was added externally to lipid vesicles at low pH, the hydrophobic face of TH1 became buried within the lipid bilayer. Helices TH2 and TH3 also inserted into the bilayer after exposure to low pH. However, in contrast to helices TH5-TH9, overall TH1-TH3 insertion was shallow and there was no significant change in TH1-TH3 insertion depth when the T domain switched from the shallowly inserting (P) to deeply inserting (TM) conformation. Binding of streptavidin to biotinylated Cys residues was used to investigate whether solution-exposed residues of membrane-inserted T domain were exposed on the external or internal surface of the bilayer. These experiments showed that when the T domain is externally added to vesicles, the entire TH1-TH3 segment remains on the cis (outer) side of the bilayer. The results of this study suggest that membrane-inserted TH1-TH3 form autonomous segments that neither deeply penetrate the bilayer nor interact tightly with the translocation-promoting structure formed by the hydrophobic TH5-TH9 subdomain. Instead, TH1-TH3 may aid translocation by acting as an A-chain-attached flexible tether.
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Affiliation(s)
- Jie Wang
- Department of Biochemistry and Cell Biology, State University of New York (SUNY)-Stony Brook, Stony Brook, New York 11794-5215, USA
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16
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White D, Musse AA, Wang J, London E, Merrill AR. Toward elucidating the membrane topology of helix two of the colicin E1 channel domain. J Biol Chem 2006; 281:32375-84. [PMID: 16854987 DOI: 10.1074/jbc.m605880200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The membrane-bound closed state of the colicin E1 channel domain was investigated by site-directed fluorescence labeling using a bimane fluorophore attached to each single cysteine residue within helix 2 of each mutant protein. The fluorescence properties of the bimane fluorophore were measured for the membrane-associated form of the closed channel and included fluorescence emission maximum, fluorescence anisotropy, apparent polarity, surface accessibility, and membrane bilayer penetration depth. The fluorescence data show that helix 2 is an amphipathic alpha-helix that is situated parallel to the membrane surface, but it is less deeply embedded within the bilayer interfacial region than is helix 1 in the closed channel. A least squares fit of the various data sets to a harmonic wave function indicated that the periodicity and angular frequency for helix 2 in the membrane-bound state are typical for an amphipathic alpha-helix (3.8 +/- 0.1 residues per turn and 94 +/- 4 degrees, respectively) that is located at an interfacial region of a membrane bilayer. Dual quencher analysis also revealed that helix 2 is peripherally membrane associated, with one face of the helix dipping into the interfacial region of the lipid bilayer and the other face projecting outwardly into the aqueous solvent. Finally, our data show that helices 1 and 2 remain independent helices upon membrane association with a short connector link (Tyr(363)-Gly(364)) and that short amphipathic alpha-helices participate in the formation of a lipid-dependent, toroidal pore for this colicin.
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Affiliation(s)
- Dawn White
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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17
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Tilley SJ, Saibil HR. The mechanism of pore formation by bacterial toxins. Curr Opin Struct Biol 2006; 16:230-6. [PMID: 16563740 DOI: 10.1016/j.sbi.2006.03.008] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Revised: 02/06/2006] [Accepted: 03/14/2006] [Indexed: 01/13/2023]
Abstract
A remarkable group of proteins challenge the notions that protein sequence determines a unique three-dimensional structure, and that membrane and soluble proteins are very distinct. The pore-forming toxins typically transform from soluble, monomeric proteins to oligomers that form transmembrane channels. Recent structural studies provide ideas about how these changes take place. The recently solved structures of the beta-pore-forming toxins LukS, epsilon-toxin and intermedilysin confirm that the pore-forming regions are initially folded up on the surfaces of the soluble precursors. To create the transmembrane pores, these regions must extend and refold into membrane-inserted beta-barrels.
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Affiliation(s)
- Sarah J Tilley
- School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK
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18
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Leng Q, MacGregor GG, Dong K, Giebisch G, Hebert SC. Subunit-subunit interactions are critical for proton sensitivity of ROMK: evidence in support of an intermolecular gating mechanism. Proc Natl Acad Sci U S A 2006; 103:1982-7. [PMID: 16446432 PMCID: PMC1413660 DOI: 10.1073/pnas.0510610103] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The tetrameric K channel ROMK provides an important pathway for K secretion by the mammalian kidney, and the gating of this channel is highly sensitive to changes in cytosolic pH. Although charge-charge interactions have been implicated in pH sensing by this K channel tetramer, the molecular mechanism linking pH sensing and the gating of ion channels is poorly understood. The x-ray crystal structure KirBac1.1, a prokaryotic ortholog of ROMK, has suggested that channel gating involves intermolecular interactions of the N- and C-terminal domains of adjacent subunits. Here we studied channel gating behavior to changes in pH using giant patch clamping of Xenopus laevis oocytes expressing WT or mutant ROMK, and we present evidence that no single charged residue provides the pH sensor. Instead, we show that N-C- and C-C-terminal subunit-subunit interactions form salt bridges, which function to stabilize ROMK in the open state and which are modified by protons. We identify a highly conserved C-C-terminal arginine-glutamate (R-E) ion pair that forms an intermolecular salt bridge and responds to changes in proton concentration. Our results support the intermolecular model for pH gating of inward rectifier K channels.
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Affiliation(s)
- Qiang Leng
- *Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8026; and
| | - Gordon G. MacGregor
- *Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8026; and
- Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, PA 15261
| | - Ke Dong
- *Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8026; and
| | - Gerhard Giebisch
- *Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8026; and
| | - Steven C. Hebert
- *Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8026; and
- To whom correspondence should be addressed. E-mail:
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Musse AA, Wang J, Deleon GP, Prentice GA, London E, Merrill AR. Scanning the Membrane-bound Conformation of Helix 1 in the Colicin E1 Channel Domain by Site-directed Fluorescence Labeling. J Biol Chem 2006; 281:885-95. [PMID: 16299381 DOI: 10.1074/jbc.m511140200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Helix 1 of the membrane-associated closed state of the colicin E1 channel domain was studied by site-directed fluorescence labeling where bimane was covalently attached to a single cysteine residue in each mutant protein. A number of fluorescence properties of the tethered bimane fluorophore were measured in the membrane-bound state of the channel domain, including fluorescence emission maximum, fluorescence quantum yield, fluorescence anisotropy, membrane bilayer penetration depth, surface accessibility, and apparent polarity. The data show that helix 1 is an amphipathic alpha-helix that is situated parallel to the membrane surface. A least squares fit of the various data sets to a harmonic function indicated that the periodicity and angular frequency for helix 1 are typical for an amphipathic alpha-helix (3.7 +/- 0.1 residues per turn and 97 +/- 3.0 degrees, respectively) that is partially bathing into the membrane bilayer. Dual fluorescence quencher analysis also revealed that helix 1 is peripherally membrane-associated, with one face of the helix dipping into the lipid bilayer and the other face projecting toward the solvent. Finally, our data suggest that the helical boundaries of helix 1, at least at the C-terminal region, remain unaffected upon binding to the surface of the membrane in support of a toroidal pore model for this colicin.
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Affiliation(s)
- Abdiwahab A Musse
- Department of Molecular and Cellular Biology, University of Guelph, Ontario, Canada
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20
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Méré J, Morlon-Guyot J, Bonhoure A, Chiche L, Beaumelle B. Acid-triggered Membrane Insertion of Pseudomonas Exotoxin A Involves an Original Mechanism Based on pH-regulated Tryptophan Exposure. J Biol Chem 2005; 280:21194-201. [PMID: 15799975 DOI: 10.1074/jbc.m412656200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Exposure to low endosomal pH during internalization of Pseudomonas exotoxin A (PE) triggers membrane insertion of its translocation domain. This process is a prerequisite for PE translocation to the cytosol where it inactivates protein synthesis. Although hydrophobic helices enable membrane insertion of related bacterial toxins such as diphtheria toxin, the PE translocation domain is devoid of hydrophobic stretches and the structural features triggering acid-induced membrane insertion of PE are not known. Here we have identified a molecular device that enables PE membrane insertion. This process is promoted by exposure of a key tryptophan residue. At neutral pH, this Trp is buried in a hydrophobic pocket closed by the smallest alpha-helix of the translocation domain. Upon acidification, protonation of the Asp that is the N-cap residue of the helix leads to its destabilization, enabling Trp side chain insertion into the endosome membrane. This tryptophan-based membrane insertion system is surprisingly similar to the membrane-anchoring mechanism of human annexin-V and could be used by other proteins as well.
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Affiliation(s)
- Jocelyn Méré
- Unite Mixte de Recherche 5539 CNRS, Case 107, Département Biologie-Santé, Université Montpellier II, 34095 Montpellier, France
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Yates SP, Merrill AR. Elucidation of eukaryotic elongation factor-2 contact sites within the catalytic domain of Pseudomonas aeruginosa exotoxin A. Biochem J 2004; 379:563-72. [PMID: 14733615 PMCID: PMC1224111 DOI: 10.1042/bj20031731] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2003] [Revised: 01/09/2004] [Accepted: 01/20/2004] [Indexed: 11/17/2022]
Abstract
Pseudomonas aeruginosa produces the virulence factor, ETA (exotoxin A), which catalyses an ADP-ribosyltransferase reaction of its target protein, eEF2 (eukaryotic elongation factor-2). Currently, this protein-protein interaction is poorly characterized and this study was aimed at identifying the contact sites between eEF2 and the catalytic domain of ETA (PE24H, an ETA from P. aeruginosa, a 24 kDa C-terminal fragment containing a His6 tag). Single-cysteine residues were introduced into the toxin at 21 defined surface-exposed sites and labelled with the fluorophore, IAEDANS [5-(2-iodoacetylaminoethylamino)-1-napthalenesulphonic acid]. Fluorescence quenching studies using acrylamide, and fluorescence lifetime and wavelength emission maxima analyses were conducted in the presence and absence of eEF2. Large changes in the microenvironment of the AEDANS [5-(2-aminoethylamino)-1-naphthalenesulphonic acid] probe after eEF2 binding were not observed as dictated by both fluorescence lifetime and wavelength emission maxima values. This supported the proposed minimal contact model, which suggests that only small, discrete contacts occur between these proteins. As dictated by the bimolecular quenching constant (k(q)) for acrylamide, binding of eEF2 with toxin caused the greatest change in acrylamide accessibility (>50%) when the fluorescence label was near the active site or was located within a known catalytic loop. All mutant proteins showed a decrease in accessibility to acrylamide once eEF2 bound, although the relative change varied for each labelled protein. From these data, a low-resolution model of the toxin-eEF2 complex was constructed based on the minimal contact model with the intention of enhancing our knowledge on the mode of inactivation of the ribosome translocase by the Pseudomonas toxin.
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Affiliation(s)
- Susan P Yates
- Department of Chemistry and Biochemistry, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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