1
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Koo S, Cheley S, Bayley H. Redirecting Pore Assembly of Staphylococcal α-Hemolysin by Protein Engineering. ACS Cent Sci 2019; 5:629-639. [PMID: 31041382 PMCID: PMC6487460 DOI: 10.1021/acscentsci.8b00910] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Indexed: 05/03/2023]
Abstract
α-Hemolysin (αHL), a β-barrel pore-forming toxin (βPFT), is secreted as a water-soluble monomer by Staphylococcus aureus. Upon binding to receptors on target cell membranes, αHL assembles to form heptameric membrane-spanning pores. We have previously engineered αHL to create a protease-activatable toxin that is activated by site-specific proteolysis including by tumor proteases. In this study, we redesigned αHL so that it requires 2-fold activation on target cells through (i) binding to specific receptors, and (ii) extracellular proteolytic cleavage. To assess our strategy, we constructed a fusion protein of αHL with galectin-1 (αHLG1, αHL-Galectin-1 chimera). αHLG1 was cytolytic toward cells that lack a receptor for wild-type αHL. We then constructed protease-activatable mutants of αHLG1 (PAMαHLG1s). PAMαHLG1s were activated by matrix metalloproteinase 2 (MMP-2) and had approximately 50-fold higher cytolytic activity toward MMP-2 overexpressing cells (HT-1080 cells) than toward non-overexpressing cells (HL-60 cells). Our approach provides a novel strategy for tailoring pore-forming toxins for therapeutic applications.
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Affiliation(s)
- Sunwoo Koo
- Department
of Neuroscience and Experimental Therapeutics, Texas A&M University Health Science Center, 8447 Riverside Parkway, Bryan, Texas 77807, United States
- E-mail: . Phone: 1-979-436-0381
| | - Stephen Cheley
- Department
of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, T6G 2E1 Alberta, Canada
| | - Hagan Bayley
- Department
of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield
Road, Oxford, OX1 3TA England, United Kingdom
- E-mail: . Phone: +44 1865 285101
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2
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Lee J, Boersma A, Boudreau MA, Cheley S, Daltrop O, Li J, Tamagaki H, Bayley H. Semisynthetic Nanoreactor for Reversible Single-Molecule Covalent Chemistry. ACS Nano 2016; 10:8843-50. [PMID: 27537396 PMCID: PMC5043417 DOI: 10.1021/acsnano.6b04663] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Accepted: 08/18/2016] [Indexed: 05/27/2023]
Abstract
Protein engineering has been used to remodel pores for applications in biotechnology. For example, the heptameric α-hemolysin pore (αHL) has been engineered to form a nanoreactor to study covalent chemistry at the single-molecule level. Previous work has been confined largely to the chemistry of cysteine side chains or, in one instance, to an irreversible reaction of an unnatural amino acid side chain bearing a terminal alkyne. Here, we present four different αHL pores obtained by coupling either two or three fragments by native chemical ligation (NCL). The synthetic αHL monomers were folded and incorporated into heptameric pores. The functionality of the pores was validated by hemolysis assays and by single-channel current recording. By using NCL to introduce a ketone amino acid, the nanoreactor approach was extended to an investigation of reversible covalent chemistry on an unnatural side chain at the single-molecule level.
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Affiliation(s)
- Joongoo Lee
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, U.K.
| | - Arnold
J. Boersma
- Groningen
Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Marc A. Boudreau
- Department
of Chemistry, University of New Hampshire, Durham, New Hampshire 03824, United States
| | - Stephen Cheley
- Department
of Pharmacology, University of Alberta, Edmonton, AB T6G 2R3, Canada
| | - Oliver Daltrop
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, U.K.
| | - Jianwei Li
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, U.K.
| | - Hiroko Tamagaki
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, U.K.
| | - Hagan Bayley
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, U.K.
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3
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Yan-Do R, Duong E, Manning Fox JE, Dai X, Suzuki K, Khan S, Bautista A, Ferdaoussi M, Lyon J, Wu X, Cheley S, MacDonald PE, Braun M. A Glycine-Insulin Autocrine Feedback Loop Enhances Insulin Secretion From Human β-Cells and Is Impaired in Type 2 Diabetes. Diabetes 2016; 65:2311-21. [PMID: 27207556 DOI: 10.2337/db15-1272] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 04/26/2016] [Indexed: 11/13/2022]
Abstract
The secretion of insulin from pancreatic islet β-cells is critical for glucose homeostasis. Disrupted insulin secretion underlies almost all forms of diabetes, including the most common form, type 2 diabetes (T2D). The control of insulin secretion is complex and affected by circulating nutrients, neuronal inputs, and local signaling. In the current study, we examined the contribution of glycine, an amino acid and neurotransmitter that activates ligand-gated Cl(-) currents, to insulin secretion from islets of human donors with and without T2D. We find that human islet β-cells express glycine receptors (GlyR), notably the GlyRα1 subunit, and the glycine transporter (GlyT) isoforms GlyT1 and GlyT2. β-Cells exhibit significant glycine-induced Cl(-) currents that promote membrane depolarization, Ca(2+) entry, and insulin secretion from β-cells from donors without T2D. However, GlyRα1 expression and glycine-induced currents are reduced in β-cells from donors with T2D. Glycine is actively cleared by the GlyT expressed within β-cells, which store and release glycine that acts in an autocrine manner. Finally, a significant positive relationship exists between insulin and GlyR, because insulin enhances the glycine-activated current in a phosphoinositide 3-kinase-dependent manner, a positive feedback loop that we find is completely lost in β-cells from donors with T2D.
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Affiliation(s)
- Richard Yan-Do
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Eric Duong
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Jocelyn E Manning Fox
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Xiaoqing Dai
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Kunimasa Suzuki
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Shara Khan
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Austin Bautista
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Mourad Ferdaoussi
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - James Lyon
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Xichen Wu
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Stephen Cheley
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Patrick E MacDonald
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Matthias Braun
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
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4
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Khan S, Yan-Do R, Duong E, Wu X, Bautista A, Cheley S, MacDonald PE, Braun M. Autocrine activation of P2Y1 receptors couples Ca (2+) influx to Ca (2+) release in human pancreatic beta cells. Diabetologia 2014; 57:2535-45. [PMID: 25208758 DOI: 10.1007/s00125-014-3368-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 08/13/2014] [Indexed: 01/26/2023]
Abstract
AIMS/HYPOTHESIS There is evidence that ATP acts as an autocrine signal in beta cells but the receptors and pathways involved are incompletely understood. Here we investigate the receptor subtype(s) and mechanism(s) mediating the effects of ATP on human beta cells. METHODS We examined the effects of purinergic agonists and antagonists on membrane potential, membrane currents, intracellular Ca(2+) ([Ca(2+)]i) and insulin secretion in human beta cells. RESULTS Extracellular application of ATP evoked small inward currents (3.4 ± 0.7 pA) accompanied by depolarisation of the membrane potential (by 14.4 ± 2.4 mV) and stimulation of electrical activity at 6 mmol/l glucose. ATP increased [Ca(2+)]i by stimulating Ca(2+) influx and evoking Ca(2+) release via InsP3-receptors in the endoplasmic reticulum (ER). ATP-evoked Ca(2+) release was sufficient to trigger exocytosis in cells voltage-clamped at -70 mV. All effects of ATP were mimicked by the P2Y(1/12/13) agonist ADP and the P2Y1 agonist MRS-2365, whereas the P2X(1/3) agonist α,β-methyleneadenosine-5-triphosphate only had a small effect. The P2Y1 antagonists MRS-2279 and MRS-2500 hyperpolarised glucose-stimulated beta cells and lowered [Ca(2+)]i in the absence of exogenously added ATP and inhibited glucose-induced insulin secretion by 35%. In voltage-clamped cells subjected to action potential-like stimulation, MRS-2279 decreased [Ca(2+)]i and exocytosis without affecting Ca(2+) influx. CONCLUSIONS/INTERPRETATION These data demonstrate that ATP acts as a positive autocrine signal in human beta cells by activating P2Y1 receptors, stimulating electrical activity and coupling Ca(2+) influx to Ca(2+) release from ER stores.
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Affiliation(s)
- Shara Khan
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada
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5
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Harrington L, Cheley S, Alexander LT, Knapp S, Bayley H. Electrostatically Enhanced Association of a Pim Kinase Substrate Revealed by Stochastic Detection. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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6
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Kong L, Harrington L, Li Q, Cheley S, Davis BG, Bayley H. Single-molecule interrogation of a bacterial sugar transporter allows the discovery of an extracellular inhibitor. Nat Chem 2013; 5:651-9. [DOI: 10.1038/nchem.1695] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Accepted: 05/24/2013] [Indexed: 11/09/2022]
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7
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Maglia G, Soskine M, Biesemans A, Bayley H, Cheley S, Moeyaert B. Engineering a Biomimetic Biological Nanopore to Selectively Capture Folded Target Proteins. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.2863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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8
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Kailey B, van de Bunt M, Cheley S, Johnson PR, MacDonald PE, Gloyn AL, Rorsman P, Braun M. SSTR2 is the functionally dominant somatostatin receptor in human pancreatic β- and α-cells. Am J Physiol Endocrinol Metab 2012; 303:E1107-16. [PMID: 22932785 PMCID: PMC3492856 DOI: 10.1152/ajpendo.00207.2012] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Somatostatin-14 (SST) inhibits insulin and glucagon secretion by activating G protein-coupled somatostatin receptors (SSTRs), of which five isoforms exist (SSTR1-5). In mice, the effects on pancreatic β-cells are mediated by SSTR5, whereas α-cells express SSTR2. In both cell types, SSTR activation results in membrane hyperpolarization and suppression of exocytosis. Here, we examined the mechanisms by which SST inhibits secretion from human β- and α-cells and the SSTR isoforms mediating these effects. Quantitative PCR revealed high expression of SSTR2, with lower levels of SSTR1, SSTR3, and SSTR5, in human islets. Immunohistochemistry showed expression of SSTR2 in both β- and α-cells. SST application hyperpolarized human β-cells and inhibited action potential firing. The membrane hyperpolarization was unaffected by tolbutamide but antagonized by tertiapin-Q, a blocker of G protein-gated inwardly rectifying K⁺ channels (GIRK). The effect of SST was mimicked by an SSTR2-selective agonist, whereas a SSTR5 agonist was marginally effective. SST strongly (>70%) reduced depolarization-evoked exocytosis in both β- and α-cells. A slightly weaker inhibition was observed in both cell types after SSTR2 activation. SSTR3- and SSTR1-selective agonists moderately reduced the exocytotic responses in β- and α-cells, respectively, whereas SSTR4- and SSTR5-specific agonists were ineffective. SST also reduced voltage-gated P/Q-type Ca²⁺ currents in β-cells, but normalization of Ca²⁺ influx to control levels by prolonged depolarizations only partially restored exocytosis. We conclude that SST inhibits secretion from both human β- and α-cells by activating GIRK and suppressing electrical activity, reducing P/Q-type Ca²⁺ currents, and directly inhibiting exocytosis. These effects are mediated predominantly by SSTR2 in both cell types.
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Affiliation(s)
- Balrik Kailey
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Oxford, United Kingdom
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9
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Soskine M, Biesemans A, Moeyaert B, Cheley S, Bayley H, Maglia G. An engineered ClyA nanopore detects folded target proteins by selective external association and pore entry. Nano Lett 2012; 12:4895-900. [PMID: 22849517 PMCID: PMC3440510 DOI: 10.1021/nl3024438] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Nanopores have been used in label-free single-molecule studies, including investigations of chemical reactions, nucleic acid analysis, and applications in sensing. Biological nanopores generally perform better than artificial nanopores as sensors, but they have disadvantages including a fixed diameter. Here we introduce a biological nanopore ClyA that is wide enough to sample and distinguish large analyte proteins, which enter the pore lumen. Remarkably, human and bovine thrombins, despite 86% sequence identity, elicit characteristic ionic current blockades, which at -50 mV differ in their main current levels by 26 ± 1 pA. The use of DNA aptamers or hirudin as ligands further distinguished the protein analytes. Finally, we constructed ClyA nanopores decorated with covalently attached aptamers. These nanopores selectively captured and internalized cognate protein analytes but excluded noncognate analytes, in a process that resembles transport by nuclear pores.
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Affiliation(s)
- Misha Soskine
- Department of Chemistry, University of Leuven, Leuven, 3001, Belgium
| | - Annemie Biesemans
- Department of Chemistry, University of Leuven, Leuven, 3001, Belgium
| | | | - Stephen Cheley
- Department of Pharmacology, University of Alberta, Edmonton, T6G 2E1, AB Canada
| | - Hagan Bayley
- Department of Chemistry, University of Oxford, Oxford, OX1 3TA, UK
| | - Giovanni Maglia
- Department of Chemistry, University of Leuven, Leuven, 3001, Belgium
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10
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Abstract
Styryl dyes are widely used to study synaptic vesicle (SV) recycling in neurons; vesicles are loaded with dye during endocytosis, and dye is subsequently released via exocytosis. During putative kiss-and-run exocytosis, efflux of dye from individual SVs has been proposed to occur via two sequential steps: dissociation from the membrane followed by permeation through a small fusion pore. To improve our understanding of the kinetics of efflux of dye from vesicles during kiss-and-run events, we examined the rates of efflux of different dyes through nanometer-scale pores formed in membranes by the toxins melittin and α-hemolysin; these pores approximate the size of fusion pores measured in neuroendocrine cells. We found that the axial diameter of each dye was a crucial determinant for permeation. Moreover, the two dyes with the largest cross-sectional areas were completely unable to pass through pores formed by a mutant α-hemolysin that has a slightly smaller pore than the wild-type toxin. The overall time constant for efflux (seconds) of each dye was orders of magnitude slower than the time constant for dissociation from membranes (milliseconds). Thus, the permeation step is rate-limiting, and this observation was further supported by atomistic molecular dynamics simulations. Together, the data reported here help provide a framework for interpreting dye destaining rates from secretory vesicles.
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Affiliation(s)
- Yao Wu
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin 53706, United States
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11
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Abstract
An improved method for the semisynthesis of a potassium channel involving native chemical ligation allows the introduction of short sequences containing non-canonical amino acids at any position within the polypeptide chain. The work enhances the technology available for a range of fundamental investigations of membrane proteins and for applications of membrane channels and pores in biotechnology.
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Affiliation(s)
- Hagan Bayley
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Stephen Cheley
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Leon Harrington
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Ruhma Syeda
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
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12
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Maglia G, Henricus M, Wyss R, Li Q, Cheley S, Bayley H. DNA strands from denatured duplexes are translocated through engineered protein nanopores at alkaline pH. Nano Lett 2009; 9:3831-3836. [PMID: 19645477 DOI: 10.1021/nl9020232] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Nanopores are under development for the detection of a variety of analytes and the investigation of chemical reactions at the single molecule level. In particular, the analysis of nucleic acid molecules is under intense investigation, including the development of systems for rapid, low-cost DNA sequencing. Here, we show that DNA can be translocated through an engineered alphaHL protein pore at pH 11.7, a value at which dsDNA is denatured. Therefore, the alphaHL pore is sufficiently stable to entertain the possibility of direct nanopore sequencing of genomic dsDNA samples, which are more readily obtained and handled than ssDNA.
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Affiliation(s)
- Giovanni Maglia
- Department of Chemistry, University of Oxford, Oxford, OX1 3TA, United Kingdom
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13
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Maglia G, Heron AJ, Hwang WL, Holden MA, Mikhailova E, Li Q, Cheley S, Bayley H. Droplet networks with incorporated protein diodes show collective properties. Nat Nanotechnol 2009; 4:437-40. [PMID: 19581896 DOI: 10.1038/nnano.2009.121] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2009] [Accepted: 04/28/2009] [Indexed: 05/02/2023]
Abstract
Recently, we demonstrated that submicrolitre aqueous droplets submerged in an apolar liquid containing lipid can be tightly connected by means of lipid bilayers to form networks. Droplet interface bilayers have been used for rapid screening of membrane proteins and to form asymmetric bilayers with which to examine the fundamental properties of channels and pores. Networks, meanwhile, have been used to form microscale batteries and to detect light. Here, we develop an engineered protein pore with diode-like properties that can be incorporated into droplet interface bilayers in droplet networks to form devices with electrical properties including those of a current limiter, a half-wave rectifier and a full-wave rectifier. The droplet approach, which uses unsophisticated components (oil, lipid, salt water and a simple pore), can therefore be used to create multidroplet networks with collective properties that cannot be produced by droplet pairs.
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Affiliation(s)
- Giovanni Maglia
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK
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14
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Wolfe AJ, Mohammad MM, Cheley S, Bayley H, Movileanu L. Catalyzing the translocation of polypeptides through attractive interactions. J Am Chem Soc 2007; 129:14034-41. [PMID: 17949000 DOI: 10.1021/ja0749340] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Facilitated translocation of polypeptides through a protein pore is a ubiquitous and fundamental process in biology. Several translocation systems possess various well-defined binding sites within the pore lumen, but a clear mechanistic understanding of how the interaction of the polypeptides with the binding site alters the underlying kinetics is still missing. Here, we employed rational protein design and single-channel electrical recordings to obtain detailed kinetic signatures of polypeptide translocation through the staphylococcal alpha-hemolysin (alphaHL) transmembrane pore, a robust, tractable, and versatile beta-barrel protein. Acidic binding sites composed of rings of negatively charged aspartic acid residues, engineered at strategic positions within the beta barrel, produced dramatic changes in the functional properties of the alphaHL protein, facilitating the transport of cationic polypeptides from one side of the membrane to the other. When two electrostatic binding sites were introduced, at the entry and exit of the beta barrel, both the rate constants of association and dissociation increased substantially, diminishing the free energy barrier for translocation. By contrast, more hydrophobic polypeptides exhibited a considerable decrease in the rate constant of association to the pore lumen, having to overcome a greater energetic barrier because of the hydrophilic nature of the pore interior.
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Affiliation(s)
- Aaron J Wolfe
- Department of Physics, Syracuse University, 201 Physics Building, Syracuse, New York 13244-1130, USA
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15
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Das SK, Darshi M, Cheley S, Wallace MI, Bayley H. Membrane protein stoichiometry determined from the step-wise photobleaching of dye-labelled subunits. Chembiochem 2007; 8:994-9. [PMID: 17503420 DOI: 10.1002/cbic.200600474] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Somes K Das
- Department of Molecular & Cellular Medicine, The Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA
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16
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Abstract
The rapid quantification of the enantiomers of small chiral molecules is very important, notably in pharmacology. Here, we show that the enantiomers of drug molecules can be distinguished by stochastic sensing, a single-molecule detection technique. The sensing element is an engineered alpha-hemolysin protein pore, fitted with a beta-cyclodextrin adapter. By using the approach, the enantiomeric composition of samples of ibuprofen and thalidomide can be determined in less than 1 s.
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Affiliation(s)
- Xiao-Feng Kang
- Department of Molecular and Cellular Medicine, The Texas A and M University System Health Science Center, College Station, Texas 77843-1114, USA
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17
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Abstract
A robust, portable chip containing a single protein nanopore would be a significant development in the practical application of stochastic sensing technology. Here, we describe a chip in which a single alpha-hemolysin (alphaHL) pore in a planar phospholipid bilayer is sandwiched between two layers of agarose gel. These encapsulated nanopore chips remain functional after storage for weeks. The detection of the second messenger inositol 1,4,5-trisphosphate (IP3) was demonstrated with a chip containing a genetically engineered alphaHL pore as the sensor element.
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Affiliation(s)
- Xiao-feng Kang
- Department of Molecular and Cellular Medicine, The Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA
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18
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Abstract
Stochastic sensing is an emerging approach for the detection of a wide variety of analytes at the level of individual molecules. Detection is accomplished by observing the modulation of the current that flows through a single protein pore that has been engineered to bind an analyte of interest. Previously, protein analytes have been detected by using pores to which ligands have been appended at specific sites by targeted chemical modification. Here, we report the first genetically encoded stochastic sensor element for detecting a protein. A protein kinase inhibitor peptide sequence was incorporated into the alpha-hemolysin polypeptide, which was used to form a heteroheptameric pore containing a single copy of the inhibitor sequence. With this pore, the successful detection of the catalytic subunit of protein kinase A was demonstrated. This development should greatly facilitate the detection of active kinase subunits by stochastic sensing and the rapid screening of kinase inhibitors by an approach that yields kinetic information.
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Affiliation(s)
- Stephen Cheley
- Department of Molecular and Cellular Medicine, The Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA
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19
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Abstract
Engineered versions of the transmembrane protein pore alpha-hemolysin (alphaHL) can be used as stochastic sensing elements for the identification and quantification of a wide variety of analytes at the single-molecule level. Until now, nitroaromatic analytes have eluded detection by this approach. We now report that binding sites for nitroaromatics can be built within the lumen of the alphaHL pore from simple rings of seven aromatic amino acid side chains (Phe, Tyr or Trp). By monitoring the ionic current that passes through a single pore at a fixed applied potential, various nitroaromatics can be distinguished from TNT on the basis of the amplitude and duration of individual current-blocking events. Rings of less than seven aromatics bind the analytes more weakly; this suggests that direct aromatic-aromatic interactions are involved. The engineered pores should be useful for the detection of explosives and, in combination with computational approaches and structural analysis, they could further our understanding of noncovalent interactions between aromatic molecules.
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Affiliation(s)
- Xiyun Guan
- Department of Medical Biochemistry & Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA
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20
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Jung Y, Cheley S, Braha O, Bayley H. The internal cavity of the staphylococcal alpha-hemolysin pore accommodates approximately 175 exogenous amino acid residues. Biochemistry 2005; 44:8919-29. [PMID: 15966717 DOI: 10.1021/bi0473713] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The cavity within the cap domain of the transmembrane staphylococcal alpha-hemolysin (alphaHL) pore is roughly a sphere of diameter approximately 45 A (molecular surface volume approximately 39,500 A(3)). We tested the ability of the cavity to accommodate exogenous polypeptide chains. Concatemerized Gly/Ser-containing sequences ("loops", L; number of repeats = n; number of residues = 10n + 5, n = 0-21) were inserted at a position located within the cavity of the fully assembled heptameric alphaHL pore. Homomeric pores containing 25 or less residues in each loop (n <or= 2) could be assembled. The pores were protease-resistant, indicating that they had been formed correctly, and produced currents in planar lipid bilayers. The pores showed an up to 70% reduction in unitary conductance, depending on the length of the inserted loop. Protease-resistant heteromeric pores containing wild-type (W) and L subunits were also assembled: when n = 3, up to five L subunits were tolerated; when n = 4, three L subunits were tolerated; and when n = 5 or 6, two L subunits were tolerated. For n >or= 7, only one L subunit was incorporated. As the inserted loop was lengthened, transient closures were observed in planar bilayer experiments with single pores. However, L(1)W(6) pores with very long loops (n = 14 and 21) had unitary conductance values close to those of W(7), suggesting that the loop is extruded through the opening in the cap of the pore into the external medium. Further analysis of bilayer recordings and electrophoretic migration patterns indicates that the upper capacity of the cavity is approximately 175 amino acids. The findings suggest that small functional peptides or proteins might be assembled within the alphaHL pore.
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Affiliation(s)
- Yuni Jung
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA
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Xie H, Braha O, Gu LQ, Cheley S, Bayley H. Single-molecule observation of the catalytic subunit of cAMP-dependent protein kinase binding to an inhibitor peptide. ACTA ACUST UNITED AC 2005; 12:109-20. [PMID: 15664520 DOI: 10.1016/j.chembiol.2004.11.013] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2004] [Revised: 11/04/2004] [Accepted: 11/05/2004] [Indexed: 11/17/2022]
Abstract
An engineered version of the staphylococcal alpha-hemolysin protein pore, bearing a peptide inhibitor near the entrance to the beta barrel, interacts with the catalytic (C) subunit of cAMP-dependent protein kinase. By monitoring the ionic current through the pore, binding events are detected at the single-molecule level. The kinetic and thermodynamic constants governing the binding interaction and the synergistic effect of MgATP are comparable but not identical to the values in bulk solution. Further, the values are strongly dependent on the applied membrane potential. Additional exploration of these findings may lead to a better understanding of the properties of enzymes at the lipid/water interface. Despite the complications, we suggest that the engineered pore might be used as a sensor element to screen inhibitors that act at either the substrate or ATP binding sites of the C subunit.
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Affiliation(s)
- Hongzhi Xie
- Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, 440 Reynolds Medical Building, College Station, TX 77843-1114, USA
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Affiliation(s)
- Xiao-Feng Kang
- Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA
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Sánchez-Quesada J, Saghatelian A, Cheley S, Bayley H, Ghadiri MR. Cover Picture: Single DNA Rotaxanes of a Transmembrane Pore Protein (Angew. Chem. Int. Ed. 23/2004). Angew Chem Int Ed Engl 2004. [DOI: 10.1002/anie.200490069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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25
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Sánchez-Quesada J, Saghatelian A, Cheley S, Bayley H, Ghadiri MR. Single DNA Rotaxanes of a Transmembrane Pore Protein. Angew Chem Int Ed Engl 2004. [DOI: 10.1002/ange.200453907] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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26
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Sánchez-Quesada J, Saghatelian A, Cheley S, Bayley H, Ghadiri MR. Titelbild: Single DNA Rotaxanes of a Transmembrane Pore Protein (Angew. Chem. 23/2004). Angew Chem Int Ed Engl 2004. [DOI: 10.1002/ange.200490069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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27
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Gu LQ, Cheley S, Bayley H. Electroosmotic enhancement of the binding of a neutral molecule to a transmembrane pore. Proc Natl Acad Sci U S A 2003; 100:15498-503. [PMID: 14676320 PMCID: PMC307596 DOI: 10.1073/pnas.2531778100] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2003] [Indexed: 11/18/2022] Open
Abstract
The flux of solvent water coupled to the transit of ions through protein pores is considerable. The effect of this electroosmotic solvent flow on the binding of a neutral molecule [beta-cyclodextrin (betaCD)] to sites within the staphylococcal alpha-hemolysin pore was investigated. Mutant alpha-hemolysin pores were used to which betaCD can bind from either entrance and through which the direction of water flow can be controlled by choosing the charge selectivity of the pore and the polarity of the applied potential. The Kd values for betaCD for individual mutant pores varied by >100-fold with the applied potential over a range of -120 to +120 mV. In all cases, the signs of the changes in binding free energy and the influence of potential on the association and dissociation rate constants for betaCD were consistent with an electroosmotic effect.
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Affiliation(s)
- Li-Qun Gu
- Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA
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Abstract
Polymer dynamics are of fundamental importance in materials science, biotechnology, and medicine. However, very little is known about the kinetics of partitioning of flexible polymer molecules into pores of nanometer dimensions. We employed electrical recording to probe the partitioning of single poly(ethylene glycol) (PEG) molecules, at concentrations near the dilute regime, into the transmembrane beta-barrel of individual protein pores formed from staphylococcal alpha-hemolysin (alphaHL). The interactions of the alpha-hemolysin pore with the PEGs (M(w) 940-6000 Da) fell into two classes: short-duration events (tau approximately 20 micro s), approximately 85% of the total, and long-duration events (tau approximately 100 micro s), approximately 15% of the total. The association rate constants (k(on)) for both classes of events were strongly dependent on polymer mass, and values of k(on) ranged over two orders of magnitude. By contrast, the dissociation rate constants (k(off)) exhibited a weak dependence on mass, suggesting that the polymer chains are largely compacted before they enter the pore, and do not decompact to a significant extent before they exit. The values of k(on) and k(off) were used to determine partition coefficients (Pi) for the PEGs between the bulk aqueous phase and the pore lumen. The low values of Pi are in keeping with a negligible interaction between the PEG chains and the interior surface of the pore, which is independent of ionic strength. For the long events, values of Pi decrease exponentially with polymer mass, according to the scaling law of Daoud and de Gennes. For PEG molecules larger than approximately 5 kDa, Pi reached a limiting value suggesting that these PEG chains cannot fit entirely into the beta-barrel.
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Affiliation(s)
- Liviu Movileanu
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA
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Acker JP, Lu XM, Young V, Cheley S, Bayley H, Fowler A, Toner M. Measurement of trehalose loading of mammalian cells porated with a metal-actuated switchable pore. Biotechnol Bioeng 2003; 82:525-32. [PMID: 12652476 DOI: 10.1002/bit.10599] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Efforts to improve the tolerance of mammalian cells to desiccation have focused on the role that sugars have in protecting cells from lethal injury. Among the key determinants of desiccation tolerance is the intracellular trehalose concentration, and thus quantifying the amount and rate of trehalose accumulation has now become very critical to the success of these desiccation approaches. We introduced trehalose into 3T3 fibroblasts, human keratinocytes, and rat hepatocytes using a genetically engineered mutant of the pore-forming alpha-hemolysin from Staphylococcus aureus. Manipulating the extracellular Zn(2+) concentration selectively opens and closes this pore ( approximately 2 nm) and enables controlled loading of cells with sugars. We quantified intracellular trehalose using gas chromatography-mass spectroscopy (GC-MS) to examine the trimethylsilyl derivative of intracellular trehalose. Using the GC-MS method, we demonstrate that the switchable characteristics of H5 alpha-hemolysin permit controlled loading of the high concentrations of trehalose (up to 0.5 M) necessary for engineering desiccation tolerance in mammalian cells.
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Affiliation(s)
- Jason P Acker
- The Center for Engineering in Medicine and Surgical Services, Massachusetts General Hospital, Harvard Medical School, and Shriners Hospitals for Children, 51 Blossom Street, Room 266, Boston, Massachusetts 02114, USA
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Affiliation(s)
- Seong-Ho Shin
- The Texas A&M University System Health Science Center Department of Medical Biochemistry & Genetics 440 Reynolds Medical Building College Station, TX 77843-1114, USA
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Abstract
Caged reagents are photoactivatable molecules with applications in biological research. While a great deal of work has been carried out on small caged molecules, less has been done on caged macromolecules, such as proteins. Caged proteins would be especially useful in signal transduction research. Since most proteins involved in cell signaling are regulated by phosphorylation, a means to cage phosphorylated proteins would be generally applicable. Here we show that the catalytic subunit of protein kinase A can be activated by thiophosphorylation at Thr-197. The modified protein can then be caged with 4-hydroxyphenacyl bromide to yield a derivative with a specific catalytic activity that is reduced by approximately 17-fold. Upon photolysis at near UV wavelengths, an approximately 15-fold increase in activity is observed, representing an approximately 85-90% yield of uncaged product with a quantum yield phi(P) = 0.21. Because protein kinases belong to a superfamily with structurally related catalytic domains, the protein chemistry demonstrated here should be applicable to a wide range of signaling proteins.
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Affiliation(s)
- Keyong Zou
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA
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Abstract
The introduction of a ring of arginine residues near the constriction in the transmembrane beta barrel of the staphylococcal alpha-hemolysin heptamer yielded a pore that could be almost completely blocked by phosphate anions at pH 7.5. Block did not occur with other oxyanions, including nitrate, sulfate, perchlorate, and citrate. Based on this finding, additional pores were engineered with high affinities for important cell signaling molecules, such as the Ca(2+)-mobilizing second messenger inositol 1,4,5-trisphosphate (IP(3)), that contain phosphate groups. One of these engineered pores, P(RR-2), provides a ring of fourteen arginines that project into the lumen of the transmembrane barrel. Remarkably, P(RR-2) bound IP(3) with low nanomolar affinity while failing to bind another second messenger, adenosine 3', 5'-cyclic monophosphate (cAMP). The engineered alpha-hemolysin pores may be useful as components of stochastic sensors for cell signaling molecules.
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Affiliation(s)
- Stephen Cheley
- Department of Medical Biochemistry and Genetics, The Texas A & M University System Health Science Center, College Station, TX 77843, USA.
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Abstract
The gene encoding hemolysin II (HlyII) was amplified from Bacillus cereus genomic DNA and a truncated mutant, HlyII(DeltaCT), was constructed lacking the 94 amino acid extension at the C terminus. The proteins were produced in an E. coli cell-free in vitro transcription and translation system, and were shown to assemble into SDS-stable oligomers on rabbit erythrocyte membranes and liposomes. The hemolytic activity of HlyII was measured with rabbit erythrocytes yielding an HC(50) value of 1.64 ng mL(-1), which is over 15 times more potent than staphylococcal alpha-hemolysin. HlyII(DeltaCT) was about eight times less potent than HlyII in this assay. Limited proteolysis of the oligomers formed by HlyII and HlyII(DeltaCT) on red cell membranes showed that the C-terminal extension is sensitive to digestion, while HlyII(DeltaCT) is protease resistant and migrates with an electrophoretic mobility similar to that of digested HlyII. HlyII forms moderately anion selective, rectifying pores (I(+80)/I(-80) = 0.57, 1 M KCl, pH 7.4) in planar lipid bilayers of diphytanoylphosphatidylcholine with a unitary conductance of 637 pS (1 M KCl, 5 mM HEPES, pH 7.4) and exhibits no gating over a wide range of applied potentials (-160 to +160 mV). In addition, it was demonstrated that HlyII forms a homoheptameric pore by using gel shift electrophoresis aided by a genetically encoded oligoaspartate tag. Although they share limited primary sequence identity (30%), these data confirm that HlyII is a structural and functional homolog of staphylococcal alpha-hemolysin.
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Affiliation(s)
- George Miles
- Department of Medical Biochemistry & Genetics, The Texas A&M University System Health Science Center, 440 Reynolds Medical Building, College Station, TX 77843-1114, USA
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Acker JP, Fowler A, Lauman B, Cheley S, Toner M. Survival of Desiccated Mammalian Cells: Beneficial Effects of Isotonic Media. ACTA ACUST UNITED AC 2002. [DOI: 10.1089/153834402320882638] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Abstract
Noncovalent molecular adapters, such as cyclodextrins, act as binding sites for channel blockers when lodged in the lumen of the alpha-hemolysin (alphaHL) pore, thereby offering a basis for the detection of a variety of organic molecules with alphaHL as a sensor element. beta-Cyclodextrin (betaCD) resides in the wild-type alphaHL pore for several hundred microseconds. The residence time can be extended to several milliseconds by the manipulation of pH and transmembrane potential. Here, we describe mutant homoheptameric alphaHL pores that are capable of accommodating betaCD for tens of seconds. The mutants were obtained by site-directed mutagenesis at position 113, which is a residue that lies near a constriction in the lumen of the transmembrane beta barrel, and fall into two classes. Members of the tight-binding class, M113D, M113N, M113V, M113H, M113F and M113Y, bind betaCD approximately 10(4)-fold more avidly than the remaining alphaHL pores, including WT-alphaHL. The lower K(d) values of these mutants are dominated by reduced values of k(off). The major effect of the mutations is most likely a remodeling of the binding site for betaCD in the vicinity of position 113. In addition, there is a smaller voltage-sensitive component of the binding, which is also affected by the residue at 113 and may result from transport of the neutral betaCD molecule by electroosmotic flow. The mutant pores for which the dwell time of betaCD is prolonged can serve as improved components for stochastic sensors.
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Affiliation(s)
- Li-Qun Gu
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, TX 77843
| | - Stephen Cheley
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, TX 77843
| | - Hagan Bayley
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, TX 77843
- Department of Chemistry, Texas A&M University, College Station, TX 77843
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37
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Chen T, Acker JP, Eroglu A, Cheley S, Bayley H, Fowler A, Toner M. Beneficial effect of intracellular trehalose on the membrane integrity of dried mammalian cells. Cryobiology 2001; 43:168-81. [PMID: 11846471 DOI: 10.1006/cryo.2001.2360] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently, there has been much interest in using trehalose and other small carbohydrates to preserve mammalian cells in the dried state as an alternative to cryopreservation. Here, we report on the successful preservation of plasma membrane integrity after drying, as a first step toward full preservation of mammalian cells. Trehalose was introduced into cells using a genetically engineered version of alpha-hemolysin, a pore-forming protein; the cells were then dried and stored for weeks at different temperatures with approximately 90% recovery of the intact plasma membrane. We show that protection of the plasma membrane by internal trehalose is dose dependent and estimate the amount of internal trehalose required for adequate protection to be approximately 10(10) molecules/cell. In addition, a minimal amount of water (approximately 15 wt%) appears to be necessary. These results show that a key component of mammalian cells can be preserved in a dried state for weeks under mild conditions (-20 degrees C and 5% relative humidity) and thereby suggest new approaches to preserving mammalian cells.
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Affiliation(s)
- T Chen
- The Center for Engineering in Medicine and Surgical Services, Boston, MA 02114, U.S.A
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38
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Abstract
The genes encoding the F and S components of a leukocidin, LukF (HlgB) and LukS (HlgC), a pore-forming binary toxin, were amplified from the Smith 5R strain of Staphylococcus aureus both with and without sequences encoding 3'-hexahistidine tags. The His-tagged components were expressed in Escherichia coli and purified under nondenaturing conditions. In addition, the two unmodified proteins and the His-tagged versions were produced in an E. coli cell-free in vitro transcription and translation system. An SDS-stable oligomer of approximately 200 kDa appeared when both components were cotranslated in the presence of rabbit erythrocyte membranes. Hemolytic activity of the combined components against rabbit erythrocytes was measured for both in vitro- and in vivo-produced polypeptides, yielding similar HC(50) values of approximately 0.14 microg/mL. The pore-forming properties of the recombinant leukocidin were also investigated with planar lipid bilayers of diphytanoylphosphatidylcholine. Although leukocidins and staphylococcal alpha-hemolysin share partial sequence identity and related folds, LukF and LukS produce a pore with a unitary conductance of 2.5 nS [1 M KCl and 5 mM HEPES (pH 7.4)], which is more than 3 times greater than that of alpha-hemolysin measured under the same conditions. Therefore, if the leukocidin pore were a cylinder, its diameter would be almost twice that of alpha-hemolysin. In addition, the leukocidin pore is weakly cation selective and exhibits gating at low positive potentials, while alpha-hemolysin is weakly anion selective and gates only at high potentials. Taken together, these data suggest that the structure of the oligomeric pore formed by the leukocidin examined here has diverged significantly from that of alpha-hemolysin.
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Affiliation(s)
- G Miles
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA
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Abstract
We describe biosensor elements that are capable of identifying individual DNA strands with single-base resolution. Each biosensor element consists of an individual DNA oligonucleotide covalently attached within the lumen of the alpha-hemolysin (alphaHL) pore to form a "DNA-nanopore". The binding of single-stranded DNA (ssDNA) molecules to the tethered DNA strand causes changes in the ionic current flowing through a nanopore. On the basis of DNA duplex lifetimes, the DNA-nanopores are able to discriminate between individual DNA strands up to 30 nucleotides in length differing by a single base substitution. This was exemplified by the detection of a drug resistance-conferring mutation in the reverse transcriptase gene of HIV. In addition, the approach was used to sequence a complete codon in an individual DNA strand tethered to a nanopore.
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Affiliation(s)
- S Howorka
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, 440 Reynolds Medical Building, College Station, TX 77843-1114, USA.
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Movileanu L, Cheley S, Howorka S, Braha O, Bayley H. Location of a constriction in the lumen of a transmembrane pore by targeted covalent attachment of polymer molecules. J Gen Physiol 2001; 117:239-52. [PMID: 11222628 PMCID: PMC2225620 DOI: 10.1085/jgp.117.3.239] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Few methods exist for obtaining the internal dimensions of transmembrane pores for which 3-D structures are lacking or for showing that structures determined by crystallography reflect the internal dimensions of pores in lipid bilayers. Several approaches, involving polymer penetration and transport, have revealed limiting diameters for various pores. But, in general, these approaches do not indicate the locations of constrictions in the channel lumen. Here, we combine cysteine mutagenesis and chemical modification with sulfhydryl-reactive polymers to locate the constriction in the lumen of the staphylococcal alpha-hemolysin pore, a model protein of known structure. The rates of reaction of each of four polymeric reagents (MePEG-OPSS) of different masses towards individual single cysteine mutants, comprising a set with cysteines distributed over the length of the lumen of the pore, were determined by macroscopic current recording. The rates for the three larger polymers (1.8, 2.5, and 5.0 kD) were normalized with respect to the rates of reaction with a 1.0-kD polymer for each of the seven positions in the lumen. The rate of reaction of the 5.0-kD polymer dropped dramatically at the centrally located Cys-111 residue and positions distal to Cys-111, whether the reagent was applied from the trans or the cis side of the bilayer. This semi-quantitative analysis sufficed to demonstrate that a constriction is located at the midpoint of the pore lumen, as predicted by the crystal structure, and although the constriction allows a 2.5-kD polymer to pass, transport of a 5.0-kD molecule is greatly restricted. In addition, PEG chains gave greater reductions in pore conductance when covalently attached to the narrower regions of the lumen, permitting further definition of the interior of the pore. The procedures described here should be applicable to other pores and to related structures such as the vestibules of ion channels.
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Affiliation(s)
- L Movileanu
- Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843, USA
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41
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Abstract
We describe a heptameric protein pore that has been engineered to accommodate two different cyclodextrin adapters simultaneously within the lumen of a transmembrane beta barrel. The volume between the adapters is a cavity of approximately 4400 cubic angstroms. Analysis of single-channel recordings reveals that individual charged organic molecules can be pulled into the cavity by an electrical potential. Once trapped, an organic molecule shuttles back and forth between the adapters for hundreds of milliseconds. Such self-assembling nanostructures are of interest for the fabrication of multianalyte sensors and could provide a means to control chemical reactions.
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Affiliation(s)
- L Q Gu
- Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, TX 77843, USA
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Abstract
A recombinant form of the porin OmpG, OmpGm, lacking the signal sequence, has been expressed in Escherichia coli. After purification under denaturing conditions, the protein was refolded in the detergent Genapol X-080, where it gained a structure rich in beta sheet as evidenced by a CD spectrum similar to that of the native form. Electrophoretic analysis and limited proteolysis experiments suggested that refolded OmpGm exists in at least three forms. Nevertheless, the recombinant protein formed uniform channels in planar bilayers with a conductance of 0.81 nS (1 M NaCl, pH 7.5). Previous biochemical studies had suggested that OmpG is a monomeric porin, rather than the usual trimer. Bilayer recordings substantiated this proposal; voltage-induced closures occurred consistently in a single step, and channel block by Gd(3+) lacked the cooperativity seen with the trimeric porin OmpF. The availability of milligram amounts of a monomeric porin will be useful both for basic studies of porin function and for membrane protein engineering.
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Affiliation(s)
- S Conlan
- Department of Medical Biochemistry & Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA
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Abstract
Stochastic sensing is an emerging analytical technique that relies upon single-molecule detection. Transmembrane pores, into which binding sites for analytes have been placed by genetic engineering, have been developed as stochastic sensing elements. Reversible occupation of an engineered binding site modulates the ionic current passing through a pore in a transmembrane potential and thereby provides both the concentration of an analyte and, through a characteristic signature, its identity. Here, we show that the concentrations of two or more divalent metal ions in solution can be determined simultaneously with a single sensor element. Further, the sensor element can be permanently calibrated without a detailed understanding of the kinetics of interaction of the metal ions with the engineered pore.
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Affiliation(s)
- O Braha
- Department of Medical Biochemistry & Genetics, The Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA.
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44
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Gu LQ, Dalla Serra M, Vincent JB, Vigh G, Cheley S, Braha O, Bayley H. Reversal of charge selectivity in transmembrane protein pores by using noncovalent molecular adapters. Proc Natl Acad Sci U S A 2000; 97:3959-64. [PMID: 10760267 PMCID: PMC18124 DOI: 10.1073/pnas.97.8.3959] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In this study, the charge selectivity of staphylococcal alpha-hemolysin (alphaHL), a bacterial pore-forming toxin, is manipulated by using cyclodextrins as noncovalent molecular adapters. Anion-selective versions of alphaHL, including the wild-type pore and various mutants, become more anion selective when beta-cyclodextrin (betaCD) is lodged within the channel lumen. By contrast, the negatively charged adapter, hepta-6-sulfato-beta-cyclodextrin (s(7)betaCD), produces cation selectivity. The cyclodextrin adapters have similar effects when placed in cation-selective mutant alphaHL pores. Most probably, hydrated Cl(-) ions partition into the central cavity of betaCD more readily than K(+) ions, whereas s(7)betaCD introduces a charged ring near the midpoint of the channel lumen and confers cation selectivity through electrostatic interactions. The molecular adapters generate permeability ratios (P(K+)/P(Cl-)) over a 200-fold range and should be useful in the de novo design of membrane channels both for basic studies of ion permeation and for applications in biotechnology.
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Affiliation(s)
- L Q Gu
- Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA
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45
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Howorka S, Movileanu L, Lu X, Magnon M, Cheley S, Braha O, Bayley H. A Protein Pore with a Single Polymer Chain Tethered within the Lumen. J Am Chem Soc 2000. [DOI: 10.1021/ja993221h] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Stefan Howorka
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Liviu Movileanu
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Xiaofeng Lu
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Melissa Magnon
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Stephen Cheley
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Orit Braha
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Hagan Bayley
- Contribution from the Department of Medical Biochemistry & Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
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Eroglu A, Russo MJ, Bieganski R, Fowler A, Cheley S, Bayley H, Toner M. Intracellular trehalose improves the survival of cryopreserved mammalian cells. Nat Biotechnol 2000; 18:163-7. [PMID: 10657121 DOI: 10.1038/72608] [Citation(s) in RCA: 398] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We report that the introduction of low concentrations of intracellular trehalose can greatly improve the survival of mammalian cells during cryopreservation. Using a genetically engineered mutant of Staphylococcus aureus alpha-hemolysin to create pores in the cellular membrane, we were able to load trehalose into cells. Low concentrations (0.2 M) of trehalose permitted long-term post-thaw survival of more than 80% of 3T3 fibroblasts and 70% of human keratinocytes. These results indicate that simplified and widely applicable freezing protocols may be possible using sugars as intracellular cryoprotective additives.
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Affiliation(s)
- A Eroglu
- The Center for Engineering in Medicine and Surgical Services, Massachusetts General Hospital, Harvard Medical School, and Shriners Hospital for Children, Boston, MA, 02114, USA
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Abstract
Extended retro (reversed) peptide sequences have not previously been accommodated within functional proteins. Here, we show that the entire transmembrane portion of the beta-barrel of the pore-forming protein alpha-hemolysin can be formed by retrosequences comprising a total of 175 amino acid residues, 25 contributed by the central sequence of each subunit of the heptameric pore. The properties of wild-type and retro heptamers in planar bilayers are similar. The single-channel conductance of the retro pore is 15% less than that of the wild-type heptamer and its current-voltage relationship denotes close to ohmic behavior, while the wild-type pore is weakly rectifying. Both wild-type and retro pores are very weakly anion selective. These results and the examination of molecular models suggest that beta-barrels may be especially accepting of retro sequences compared to other protein folds. Indeed, the ability to form a retro domain could be diagnostic of a beta-barrel, explaining, for example, the activity of the retro forms of many membrane-permeabilizing peptides. By contrast with the wild-type subunits, monomeric retro subunits undergo premature assembly in the absence of membranes, most likely because the altered central sequence fails to interact with the remainder of the subunit, thereby initiating assembly. Despite this difficulty, a technique was devised for obtaining heteromeric pores containing both wild-type and retro subunits. Most probably as a consequence of unfavorable interstrand side-chain interactions, the heteromeric pores are less stable than either the wild-type or retro homoheptamers, as judged by the presence of subconductance states in single-channel recordings. Knowledge about the extraordinary plasticity of the transmembrane beta-barrel of alpha-hemolysin will be very useful in the de novo design of functional membrane proteins based on the beta-barrel motif.
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Affiliation(s)
- S Cheley
- Department of Medical Biochemistry and Genetics, Texas A&M Health Science Center, College Station 77843-1114, USA
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Abstract
The detection of organic molecules is important in many areas, including medicine, environmental monitoring and defence. Stochastic sensing is an approach that relies on the observation of individual binding events between analyte molecules and a single receptor. Engineered transmembrane protein pores are promising sensor elements for stochastic detection, and in their simplest manifestation they produce a fluctuating binary ('on/off') response in the transmembrane electrical current. The frequency of occurrence of the fluctuations reveals the concentration of the analyte, and its identity can be deduced from the characteristic magnitude and/or duration of the fluctuations. Genetically engineered versions of the bacterial pore-forming protein alpha-haemolysin have been used to identify and quantify divalent metal ions in solution. But it is not immediately obvious how versatile binding sites for organic ligands might be obtained by engineering of the pore structure. Here we show that stochastic sensing of organic molecules can be procured from alpha-haemolysin by equipping the channel with an internal, non-covalently bound molecular 'adapter' which mediates channel blocking by the analyte. We use cyclodextrins as the adapters because these fit comfortably inside the pore and present a hydrophobic cavity suitable for binding a variety of organic analytes. Moreover, a single sensing element of this sort can be used to analyse a mixture of organic molecules with different binding characteristics. We envisage the use of other adapters, so that the pore could be 'programmed' for a range of sensing functions.
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Affiliation(s)
- L Q Gu
- Department of Medical Biochemistry & Genetics, Texas A&M University Health Science Center, College Station 77843-1114, USA
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Abstract
Atomic force microscopy has been used to study self-assembled structures of two alpha-hemolysin mutants. For a mutant (alphaHL-H5) that was locked into the prepore state on fluid phase egg-PC membranes, we visualized, for the first time, heptameric prepores and showed that the 7-fold axis in the prepore lies perpendicular to the membrane surface. For another mutant (TCM) with the transmembrane domain, the self-assembled oligomer that assumes the conformation of the fully assembled pore is also a heptamer. These results show that heptamers are the preferred oligomerization state of alpha-hemolysin.
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Affiliation(s)
- M S Malghani
- Department of Physics, University of Vermont, Burlington 05405, USA
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Kasianowicz JJ, Burden DL, Han LC, Cheley S, Bayley H. Genetically engineered metal ion binding sites on the outside of a Channel's transmembrane beta-barrel. Biophys J 1999; 76:837-45. [PMID: 9929485 PMCID: PMC1300085 DOI: 10.1016/s0006-3495(99)77247-4] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
We are exploring the ability of genetically engineered versions of the Staphylococcus aureus alpha-hemolysin (alphaHL) ion channel to serve as rationally designed sensor components for analytes including divalent cations. We show here that neither the hemolytic activity nor the single channel current of wild-type alphaHL was affected by [Zn(II)] </= 1 mM. Binding sites for the divalent cations were formed by altering the number and location of coordinating side chains, e.g., histidines and aspartic acids, between positions 126 and 134, inclusive. Several mutant alphaHLs exhibited Zn(II)-induced current noise that varied with Zn(II) concentration. At a fixed divalent cation concentration, the current fluctuation kinetics depended on the analyte type, e.g., Zn(II), Cu(II), Ni(II), and Co(II). We also show that the ability of Zn(II) to change the mutant channel current suggests that the pore's topology is beta-sheet and that position 130 is near the turn at the trans mouth. Both conclusions are consistent with the crystal structure of WT-alphaHL oligomerized in detergent. Our results, in the context of the channel's crystal structure, suggest that conductance blockades were caused by Zn(II) binding to the outside surface of the pore. Thus, analyte-induced current blockades alone might not establish whether an analyte binding site is inside a pore.
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Affiliation(s)
- J J Kasianowicz
- National Institute of Standards and Technology, Biotechnology Division, Gaithersburg, Maryland 20899, USA.
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