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Torres J, Surya W, Boonserm P. Channel Formation in Cry Toxins: An Alphafold-2 Perspective. Int J Mol Sci 2023; 24:16809. [PMID: 38069132 PMCID: PMC10705909 DOI: 10.3390/ijms242316809] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 11/23/2023] [Accepted: 11/24/2023] [Indexed: 12/18/2023] Open
Abstract
Bacillus thuringiensis (Bt) strains produce pore-forming toxins (PFTs) that attack insect pests. Information for pre-pore and pore structures of some of these Bt toxins is available. However, for the three-domain (I-III) crystal (Cry) toxins, the most used Bt toxins in pest control, this crucial information is still missing. In these Cry toxins, biochemical data have shown that 7-helix domain I is involved in insertion in membranes, oligomerization and formation of a channel lined mainly by helix α4, whereas helices α1 to α3 seem to have a dynamic role during insertion. In the case of Cry1Aa, toxic against Manduca sexta larvae, a tetrameric oligomer seems to precede membrane insertion. Given the experimental difficulty in the elucidation of the membrane insertion steps, we used Alphafold-2 (AF2) to shed light on possible oligomeric structural intermediates in the membrane insertion of this toxin. AF2 very accurately (<1 Å RMSD) predicted the crystal monomeric and trimeric structures of Cry1Aa and Cry4Ba. The prediction of a tetramer of Cry1Aa, but not Cry4Ba, produced an 'extended model' where domain I helices α3 and α2b form a continuous helix and where hydrophobic helices α1 and α2 cluster at the tip of the bundle. We hypothesize that this represents an intermediate that binds the membrane and precedes α4/α5 hairpin insertion, together with helices α6 and α7. Another Cry1Aa tetrameric model was predicted after deleting helices α1 to α3, where domain I produced a central cavity consistent with an ion channel, lined by polar and charged residues in helix α4. We propose that this second model corresponds to the 'membrane-inserted' structure. AF2 also predicted larger α4/α5 hairpin n-mers (14 ≤n ≤ 17) with high confidence, which formed even larger (~5 nm) pores. The plausibility of these models is discussed in the context of available experimental data and current paradigms.
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Affiliation(s)
- Jaume Torres
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
| | - Wahyu Surya
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
| | - Panadda Boonserm
- Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom 73170, Thailand;
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Souissi W, Alistair T, Domanska B, Fortea E, West MJ, Schwartz JL, Crickmore N. Probing the Mechanism of Action of Cry41Aa on HepG2 through the Establishment of a Resistant Subline. Toxins (Basel) 2022; 14:319. [PMID: 35622566 PMCID: PMC9147150 DOI: 10.3390/toxins14050319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Revised: 04/27/2022] [Accepted: 04/28/2022] [Indexed: 11/16/2022] Open
Abstract
Cry41Aa, also called parasporin-3, belongs to a group of toxins from the entomopathogenic bacterium Bacillus thuringiensis that show activity against human cancer cells. Cry41Aa exhibits preferential cytocidal activity towards HL-60 (human promyelocytic leukaemia cells) and HepG2 (human liver cancer cells) cell lines after being proteolytically activated. To better understand the mechanism of action of Cry41Aa, we evolved resistance in HepG2 cells through repeated exposure to increasing doses of the toxin. Concentrations of Cry41Aa that killed over 50% of the parental HepG2 cells had no significant effect on the viability of the resistant cells and did not induce either pore formation or p38 phosphorylation (both characteristic features of pore-forming toxins). Preliminary RNA sequencing data identified AQP9 as a potential mediator of resistance, but extensive investigations failed to show a causal link and did not support an enhanced cell repair process as the resistance mechanism.
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Affiliation(s)
- Wided Souissi
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK; (T.A.); (B.D.); (M.J.W.); (N.C.)
| | - Tweedie Alistair
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK; (T.A.); (B.D.); (M.J.W.); (N.C.)
| | - Barbara Domanska
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK; (T.A.); (B.D.); (M.J.W.); (N.C.)
| | - Eva Fortea
- Departement of Pharmacology et Physiology, University of Montreal, Montreal, QC H3C 3J7, Canada; (E.F.); (J.-L.S.)
| | - Michelle J. West
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK; (T.A.); (B.D.); (M.J.W.); (N.C.)
| | - Jean-Louis Schwartz
- Departement of Pharmacology et Physiology, University of Montreal, Montreal, QC H3C 3J7, Canada; (E.F.); (J.-L.S.)
| | - Neil Crickmore
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK; (T.A.); (B.D.); (M.J.W.); (N.C.)
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3
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Zaitseva J, Vaknin D, Krebs C, Doroghazi J, Milam SL, Balasubramanian D, Duck NB, Freigang J. Structure-function characterization of an insecticidal protein GNIP1Aa, a member of an MACPF and β-tripod families. Proc Natl Acad Sci U S A 2019; 116:2897-2906. [PMID: 30728296 PMCID: PMC6386698 DOI: 10.1073/pnas.1815547116] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The crystal structure of the Gram-negative insecticidal protein, GNIP1Aa, has been solved at 2.5-Å resolution. The protein consists of two structurally distinct domains, a MACPF (membrane attack complex/PerForin) and a previously uncharacterized type of domain. GNIP1Aa is unique in being a prokaryotic MACPF member to have both its structure and function identified. It was isolated from a Chromobacterium piscinae strain and is specifically toxic to Diabrotica virgifera virgifera larvae upon feeding. In members of the MACPF family, the MACPF domain has been shown to be important for protein oligomerization and formation of transmembrane pores, while accompanying domains define the specificity of the target of the toxicity. In GNIP1Aa the accompanying C-terminal domain has a unique fold composed of three pseudosymmetric subdomains with shared sequence similarity, a feature not obvious from the initial sequence examination. Our analysis places this domain into a protein family, named here β-tripod. Using mutagenesis, we identified functionally important regions in the β-tripod domain, which may be involved in target recognition.
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Affiliation(s)
| | | | | | | | - Sara L Milam
- Agricultural Solutions, BASF, Morrisville, NC 27560
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Latham JR, Love M, Hilbeck A. The distinct properties of natural and GM cry insecticidal proteins. Biotechnol Genet Eng Rev 2017; 33:62-96. [PMID: 28901209 DOI: 10.1080/02648725.2017.1357295] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The Cry toxins are a family of crystal-forming proteins produced by the bacterium Bacillus thuringiensis. Their mode of action is thought to be to create pores that disrupt the gut epithelial membranes of juvenile insects. These pores allow pathogen entry into the hemocoel, thereby killing the insect. Genes encoding a spectrum of Cry toxins, including Cry mutants, Cry chimaeras and other Cry derivatives, are used commercially to enhance insect resistance in genetically modified (GM) crops. In most countries of the world, such GM crops are regulated and must be assessed for human and environmental safety. However, such risk assessments often do not test the GM crop or its tissues directly. Instead, assessments rely primarily on historical information from naturally occurring Cry proteins and on data collected on Cry proteins (called 'surrogates') purified from laboratory strains of bacteria engineered to express Cry protein. However, neither surrogates nor naturally occurring Cry proteins are identical to the proteins to which humans or other nontarget organisms are exposed by the production and consumption of GM plants. To-date there has been no systematic survey of these differences. This review fills this knowledge gap with respect to the most commonly grown GM Cry-containing crops approved for international use. Having described the specific differences between natural, surrogate and GM Cry proteins this review assesses these differences for their potential to undermine the reliability of risk assessments. Lastly, we make specific recommendations for improving risk assessments.
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Affiliation(s)
| | | | - Angelika Hilbeck
- c Swiss Federal Institute of Technology (ETH), Institute of Integrative Biology , Universitätstrasse , Zurich , Switzerland
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Hayakawa T, Sakakibara A, Ueda S, Azuma Y, Ide T, Takebe S. Cry46Ab from Bacillus thuringiensis TK-E6 is a new mosquitocidal toxin with aerolysin-type architecture. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2017; 87:100-106. [PMID: 28676354 DOI: 10.1016/j.ibmb.2017.06.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 06/30/2017] [Accepted: 06/30/2017] [Indexed: 06/07/2023]
Abstract
Cry46Ab is a Cry toxin derived from Bacillus thuringiensis TK-E6. Cry46Ab is not significantly homologous to other mosquitocidal Cry or Cyt toxins and is classified as an aerolysin-type pore-forming toxin based on structural similarity. In this study, the potency of Cry46Ab was assessed for its potential application to mosquito control. A synthetic Cry46Ab gene, cry46Ab-S1, was designed to produce recombinant Cry46Ab as a glutathione-S-transferase fusion in Escherichia coli. Recombinant Cry46Ab showed apparent toxicity to Culex pipiens larvae, with a 50% lethal dose of 1.02 μg/ml. In an artificial lipid bilayer, Cry46Ab activated by trypsin caused typical current transitions between open and closed states, suggesting it functions as a pore-forming toxin similar to other Cry and Cyt toxins. The single-channel conductance was 103.3 ± 4.1 pS in 150 mM KCl. Co-administration of recombinant Cry46Ab with other mosquitocidal Cry toxins, especially the combination of Cry4Aa and Cry46Ab, resulted in significant synergistic toxicity against C. pipiens larvae. Co-administration of multiple toxins exhibiting different modes of action is believed to prevent the onset of resistance in insects. Our data, taken in consideration with the differences in its structure, suggest that Cry46Ab could be useful in not only reducing resistance levels but also improving the insecticidal activity of Bt-based bio-insecticides.
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Affiliation(s)
- Tohru Hayakawa
- Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan.
| | - Akira Sakakibara
- Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan
| | - Sho Ueda
- Graduate School of Biology-Oriented Science and Technology, Kindai University, 930 Nishimitani, Kinokawa 649-6493, Japan
| | - Yoshinao Azuma
- Graduate School of Biology-Oriented Science and Technology, Kindai University, 930 Nishimitani, Kinokawa 649-6493, Japan
| | - Toru Ide
- Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan
| | - So Takebe
- Graduate School of Biology-Oriented Science and Technology, Kindai University, 930 Nishimitani, Kinokawa 649-6493, Japan
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6
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The human cancer cell active toxin Cry41Aa from Bacillus thuringiensis acts like its insecticidal counterparts. Biochem J 2017; 474:1591-1602. [PMID: 28341807 DOI: 10.1042/bcj20170122] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 03/20/2017] [Accepted: 03/24/2017] [Indexed: 12/15/2022]
Abstract
Understanding how certain protein toxins from the normally insecticidal bacterium Bacillus thuringiensis (Bt) target human cell lines has implications for both the risk assessment of products containing these toxins and potentially for cancer therapy. This understanding requires knowledge of whether the human cell active toxins work by the same mechanism as their insecticidal counterparts or by alternative ones. The Bt Cry41Aa (also known as Parasporin3) toxin is structurally related to the toxins synthesised by commercially produced transgenic insect-resistant plants, with the notable exception of an additional C-terminal β-trefoil ricin domain. To better understand its mechanism of action, we developed an efficient expression system for the toxin and created mutations in regions potentially involved in the toxic mechanism. Deletion of the ricin domain did not significantly affect the activity of the toxin against the human HepG2 cell line, suggesting that this region was not responsible for the mammalian specificity of Cry41Aa. Various biochemical assays suggested that unlike some other human cell active toxins from Bt Cry41Aa did not induce apoptosis, but that its mechanism of action was consistent with that of a pore-forming toxin. The toxin induced a rapid and significant decrease in metabolic activity. Adenosine triphosphate depletion, cell swelling and membrane damage were also observed. An exposed loop region believed to be involved in receptor binding of insecticidal Cry toxins was shown to be important for the activity of Cry41Aa against HepG2 cells.
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Piovesan AR, Martinelli AHS, Ligabue-Braun R, Schwartz JL, Carlini CR. Canavalia ensiformis urease, Jaburetox and derived peptides form ion channels in planar lipid bilayers. Arch Biochem Biophys 2014; 547:6-17. [PMID: 24583269 DOI: 10.1016/j.abb.2014.02.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2013] [Revised: 02/13/2014] [Accepted: 02/14/2014] [Indexed: 01/22/2023]
Abstract
Ureases catalyze the hydrolysis of urea into NH3 and CO2. They are synthesized by plants, fungi and bacteria but not by animals. Ureases display biological activities unrelated to their enzymatic activity, i.e., platelet and neutrophil activation, fungus inhibition and insecticidal effect. Urease from Canavalia ensiformis (jack bean) is toxic to several hemipteran and coleopteran insects. Jaburetox is an insecticidal fragment derived from jack bean urease. Among other effects, Jaburetox has been shown to interact with lipid vesicles. In this work, the ion channel activity of C. ensiformis urease, Jaburetox and three deletion mutants of Jaburetox (one lacking the N-terminal region, one lacking the C-terminal region and one missing the central β-hairpin) were tested on planar lipid bilayers. All proteins formed well resolved, highly cation-selective channels exhibiting two conducting states whose conductance ranges were 7-18pS and 32-79pS, respectively. Urease and the N-terminal mutant of Jaburetox were more active at negative potentials, while the channels of the other peptides did not display voltage-dependence. This is the first direct demonstration of the capacity of C. ensiformis urease and Jaburetox to permeabilize membranes through an ion channel-based mechanism, which may be a crucial step of their diverse biological activities, including host defense.
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Affiliation(s)
- Angela R Piovesan
- Graduate Program in Cellular and Molecular Biology, Center of Biotechnology, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS CEP 91501-970, Brazil
| | - Anne H S Martinelli
- Graduate Program in Cellular and Molecular Biology, Center of Biotechnology, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS CEP 91501-970, Brazil; Department of Biophysics, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS CEP 91501-970, Brazil
| | - Rodrigo Ligabue-Braun
- Graduate Program in Cellular and Molecular Biology, Center of Biotechnology, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS CEP 91501-970, Brazil
| | - Jean-Louis Schwartz
- Groupe d'étude des protéines membranaires (GÉPROM, FQR-S) and Department of Physiology, Faculty of Medicine, Université de Montréal, Montreal, Quebec H3C 3J7, Canada; Centre SÈVE (FQR-NT), Université de Sherbrooke, Sherbrooke, Quebec J1K 2R, Canada.
| | - Celia R Carlini
- Graduate Program in Cellular and Molecular Biology, Center of Biotechnology, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS CEP 91501-970, Brazil; Department of Biophysics, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS CEP 91501-970, Brazil.
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Juntadech T, Kanintronkul Y, Kanchanawarin C, Katzenmeier G, Angsuthanasombat C. Importance of polarity of the α4–α5 loop residue—Asn166 in the pore-forming domain of the Bacillus thuringiensis Cry4Ba toxin: Implications for ion permeation and pore opening. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:319-27. [DOI: 10.1016/j.bbamem.2013.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 10/01/2013] [Accepted: 10/03/2013] [Indexed: 01/01/2023]
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Abstract
Many electrical properties of insect larval guts have been studied, but their importance for toxicity of the Cry-type toxins has never been reported in the literature. In the present work, we observed potential-dependent permeabilization of plasma membrane by several polycationic peptides derived from the Cry11Bb protoxin. The peptide BTM-P1d, all D-type amino acid analogue of the earlier reported peptide BTM-P1, demonstrated high membrane-permeabilizing activity in experiments with isolated rat liver mitochondria, RBC (red blood cells) and mitochondria in homogenates of Aedes aegypti larval guts. Two larger peptides, BTM-P2 and BTM-P3, as well as the Cry11Bb protoxin treated with the protease extract of mosquito larval guts showed similar effects. Only protease-resistant BTM-P1d, in comparison with other peptides, displayed A. aegypti larval toxicity. Taking into account the potential-dependent mechanism of membrane permeabilization by studied fragments of the Cry11Bb protoxin and the literature data related to the distribution of membrane and transepithelial potentials in the A. aegypti larval midgut, we suggest an electrical hypothesis of toxicity of the Cry toxins for mosquito larvae. According to this hypothesis, the electrical field distribution is one of the factors determining the midgut region most susceptible for insertion of activated toxins into the plasma membrane to form pores. In addition, potential-dependent penetration of short active toxin fragments into the epithelial cells could induce permeabilization of mitochondria and subsequent apoptosis or necrosis.
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Niedzwiecki D, Mohammad M, Movileanu L. Inspection of the engineered FhuA ΔC/Δ4L protein nanopore by polymer exclusion. Biophys J 2012; 103:2115-24. [PMID: 23200045 PMCID: PMC3512039 DOI: 10.1016/j.bpj.2012.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 10/03/2012] [Accepted: 10/10/2012] [Indexed: 12/11/2022] Open
Abstract
Extensive engineering of protein nanopores for biotechnological applications using native scaffolds requires further inspection of their internal geometry and size. Recently, we redesigned ferric hydroxamate uptake component A (FhuA), a 22-β-stranded protein containing an N-terminal 160-residue cork domain (C). The cork domain and four large extracellular loops (4L) were deleted to obtain an unusually stiff engineered FhuA ΔC/Δ4L nanopore. We employed water-soluble poly(ethylene glycols) and dextran polymers to examine the interior of FhuA ΔC/Δ4L. When this nanopore was reconstituted into a synthetic planar lipid bilayer, addition of poly(ethylene glycols) produced modifications in the single-channel conductance, allowing for the evaluation of the nanopore diameter. Here, we report that FhuA ΔC/Δ4L features an approximate conical internal geometry with the cis entrance smaller than the trans entrance, in accord with the asymmetric nature of the crystal structure of the wild-type FhuA protein. Further experiments with impermeable dextran polymers indicated an average internal diameter of ~2.4 nm, a conclusion we arrived at based upon the polymer-induced alteration of the access resistance contribution to the nanopore's total resistance. Molecular insights inferred from this work represent a platform for future protein engineering of FhuA that will be employed for specific tasks in biotechnological applications.
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Affiliation(s)
| | | | - Liviu Movileanu
- Department of Physics, Syracuse University, Syracuse, New York
- Structural Biology, Biochemistry, and Biophysics Program, Syracuse University, Syracuse, New York
- Syracuse Biomaterials Institute, Syracuse University, Syracuse, New York
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Groulx N, McGuire H, Laprade R, Schwartz JL, Blunck R. Single molecule fluorescence study of the Bacillus thuringiensis toxin Cry1Aa reveals tetramerization. J Biol Chem 2011; 286:42274-42282. [PMID: 22006922 DOI: 10.1074/jbc.m111.296103] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Pore-forming toxins constitute a class of potent virulence factors that attack their host membrane in a two- or three-step mechanism. After binding to the membrane, often aided by specific receptors, they form pores in the membrane. Pore formation either unfolds a cytolytic activity in itself or provides a pathway to introduce enzymes into the cells that act upon intracellular proteins. The elucidation of the pore-forming mechanism of many of these toxins represents a major research challenge. As the toxins often refold after entering the membrane, their structure in the membrane is unknown, and key questions such as the stoichiometry of individual pores and their mechanism of oligomerization remain unanswered. In this study, we used single subunit counting based on fluorescence spectroscopy to explore the oligomerization process of the Cry1Aa toxin of Bacillus thuringiensis. Purified Cry1Aa toxin molecules labeled at different positions in the pore-forming domain were inserted into supported lipid bilayers, and the photobleaching steps of single fluorophores in the fluorescence time traces were counted to determine the number of subunits of each oligomer. We found that toxin oligomerization is a highly dynamic process that occurs in the membrane and that tetramers represent the final form of the toxins in a lipid bilayer environment.
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Affiliation(s)
- Nicolas Groulx
- Groupe d'Étude des Protéines Membranaires (GÉPROM), Université de Montréal, Montréal, Québec H3C 3J7, Canada; Department of Physics, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Hugo McGuire
- Groupe d'Étude des Protéines Membranaires (GÉPROM), Université de Montréal, Montréal, Québec H3C 3J7, Canada; Department of Physics, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Raynald Laprade
- Groupe d'Étude des Protéines Membranaires (GÉPROM), Université de Montréal, Montréal, Québec H3C 3J7, Canada; Department of Physics, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Jean-Louis Schwartz
- Groupe d'Étude des Protéines Membranaires (GÉPROM), Université de Montréal, Montréal, Québec H3C 3J7, Canada; Centre SÈVE, Université de Montréal, Montréal, Québec H3C 3J7, Canada; Department of Physiology, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Rikard Blunck
- Groupe d'Étude des Protéines Membranaires (GÉPROM), Université de Montréal, Montréal, Québec H3C 3J7, Canada; Department of Physics, Université de Montréal, Montréal, Québec H3C 3J7, Canada; Department of Physiology, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
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Kao CY, Los FCO, Huffman DL, Wachi S, Kloft N, Husmann M, Karabrahimi V, Schwartz JL, Bellier A, Ha C, Sagong Y, Fan H, Ghosh P, Hsieh M, Hsu CS, Chen L, Aroian RV. Global functional analyses of cellular responses to pore-forming toxins. PLoS Pathog 2011; 7:e1001314. [PMID: 21408619 PMCID: PMC3048360 DOI: 10.1371/journal.ppat.1001314] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Accepted: 02/04/2011] [Indexed: 01/12/2023] Open
Abstract
Here we present the first global functional analysis of cellular responses to pore-forming toxins (PFTs). PFTs are uniquely important bacterial virulence factors, comprising the single largest class of bacterial protein toxins and being important for the pathogenesis in humans of many Gram positive and Gram negative bacteria. Their mode of action is deceptively simple, poking holes in the plasma membrane of cells. The scattered studies to date of PFT-host cell interactions indicate a handful of genes are involved in cellular defenses to PFTs. How many genes are involved in cellular defenses against PFTs and how cellular defenses are coordinated are unknown. To address these questions, we performed the first genome-wide RNA interference (RNAi) screen for genes that, when knocked down, result in hypersensitivity to a PFT. This screen identifies 106 genes (∼0.5% of genome) in seven functional groups that protect Caenorhabditis elegans from PFT attack. Interactome analyses of these 106 genes suggest that two previously identified mitogen-activated protein kinase (MAPK) pathways, one (p38) studied in detail and the other (JNK) not, form a core PFT defense network. Additional microarray, real-time PCR, and functional studies reveal that the JNK MAPK pathway, but not the p38 MAPK pathway, is a key central regulator of PFT-induced transcriptional and functional responses. We find C. elegans activator protein 1 (AP-1; c-jun, c-fos) is a downstream target of the JNK-mediated PFT protection pathway, protects C. elegans against both small-pore and large-pore PFTs and protects human cells against a large-pore PFT. This in vivo RNAi genomic study of PFT responses proves that cellular commitment to PFT defenses is enormous, demonstrates the JNK MAPK pathway as a key regulator of transcriptionally-induced PFT defenses, and identifies AP-1 as the first cellular component broadly important for defense against large- and small-pore PFTs. The plasma membrane surrounds cells and protects their interior from the environment and from attack by disease-causing agents like bacteria and viruses. Bacteria that cause disease have discovered that an effective way to attack cells is to secrete proteins (pore-forming toxins) that breach, i.e., form holes in, the plasma membrane. How cells deal with and survive this kind of attack is poorly understood. Here, we report on the first large-scale study of the genes and mRNA transcripts that respond to pore-forming toxin attack in cells. We find that a remarkable portion, >0.5%, of the cell's genome protects it against pore-forming toxins. These data led us to look more closely at mitogen-activated protein kinase pathways as regulators of pore-forming toxin defenses. We find that half of the PFT-induced protective response is controlled by a single, conserved signaling pathway in cells, which controls a complex array of downstream targets and which protects against both large pore and small pore toxins. Our results indicate that defense against pore-forming toxins is a very ancient defense that utilizes a much more complex and extensive response in cells than previously demonstrated.
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Affiliation(s)
- Cheng-Yuan Kao
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Ferdinand C. O. Los
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Danielle L. Huffman
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Shinichiro Wachi
- Center for Eukaryotic Gene Regulation, Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Nicole Kloft
- Institute of Medical Microbiology and Hygiene, University Medical Center, Johannes Gutenberg-University Mainz, Hochhaus am Augustusplatz, Mainz, Germany
| | - Matthias Husmann
- Institute of Medical Microbiology and Hygiene, University Medical Center, Johannes Gutenberg-University Mainz, Hochhaus am Augustusplatz, Mainz, Germany
| | - Valbona Karabrahimi
- Groupe d'étude des protéines membranaires, Université de Montréal, Montreal, Quebec, Canada
| | - Jean-Louis Schwartz
- Groupe d'étude des protéines membranaires, Université de Montréal, Montreal, Quebec, Canada
| | - Audrey Bellier
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Christine Ha
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Youn Sagong
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Hui Fan
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, United States of America
| | - Partho Ghosh
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, United States of America
| | - Mindy Hsieh
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Chih-Shen Hsu
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Li Chen
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Raffi V. Aroian
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America
- * E-mail:
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Freeman TC, Landry SJ, Wimley WC. The prediction and characterization of YshA, an unknown outer-membrane protein from Salmonella typhimurium. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:287-97. [PMID: 20863811 DOI: 10.1016/j.bbamem.2010.09.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 06/12/2010] [Revised: 09/13/2010] [Accepted: 09/15/2010] [Indexed: 11/27/2022]
Abstract
We have developed an effective pathway for the prediction and characterization of novel transmembrane β-barrel proteins. The Freeman-Wimley algorithm, which is a highly accurate prediction method based on the physicochemical properties of experimentally characterized transmembrane β barrel (TMBB) structures, was used to predict TMBBs in the genome of Salmonella typhimurium LT2. The previously uncharacterized product of gene yshA was tested as a model for validating the algorithm. YshA is a highly conserved 230-residue protein that is predicted to have 10 transmembrane β-strands and an N-terminal signal sequence. All of the physicochemical and spectroscopic properties exhibited by YshA are consistent with the prediction that it is a TMBB. Specifically, recombinant YshA localizes to the outer membrane when expressed in Escherichia coli; YshA has a β-sheet-rich secondary structure with stable tertiary contacts in the presence of detergent micelles or when reconstituted into a lipid bilayer. When in a lipid bilayer, YshA forms a membrane-spanning pore with an effective radius of ~0.7nm. Taken together, these data substantiate the predictions made by the Freeman-Wimley algorithm by showing that YshA is a TMBB protein.
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Affiliation(s)
- Thomas C Freeman
- Department of Biochemistry, Tulane University Health Sciences Center, 1430 Tulane Ave SL-43, New Orleans, LA 70112, USA
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Taveecharoenkool T, Angsuthanasombat C, Kanchanawarin C. Combined molecular dynamics and continuum solvent studies of the pre-pore Cry4Aa trimer suggest its stability in solution and how it may form pore. PMC BIOPHYSICS 2010; 3:10. [PMID: 20465833 PMCID: PMC3239330 DOI: 10.1186/1757-5036-3-10] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Accepted: 05/13/2010] [Indexed: 11/10/2022]
Abstract
Cry4Aa toxin is one of the highly specific mosquito-larvicidal proteins produced by the bacterium Bacillus thuringiensis subspecies israelensis. It is thought to form pores in the larval midgut membrane that cause membrane leakage and subsequent insect death. Therefore, Cry4Aa and other Cry toxins have been used as efficient and safe bacterial insecticides to control the disease-carrying mosquitoes such as Aedes, Anopheles, and Culex. However, we still do not clearly understand how Cry toxins kill mosquito-larvae at molecular details. Recent electron crystallographic images of Cry4Ba toxin, another toxin closely related to Cry4Aa toxin, have suggested that the protein forms trimer in aqueous solution and in lipid monolayer. Moreover, the unit cell of X-ray crystal structure of Cry4Ba toxin has been shown to be trimeric. In this study, we constructed the first full-atom structural model of Cry4Aa trimer using the trimeric unit cell structure of Cry4Ba toxin as a template and then used the methods of molecular dynamics (MD) and molecular mechanics combined with Poisson-Boltzmann and surface area (MM-PBSA) to show that the trimeric structure of Cry4Aa toxin is stable in 150 mM KCl solution on 10 ns timescale. The results reveal that Cry4Aa toxins use polar amino acid residues on alpha-helices 3, 4, and 6 to form trimer and suggest that the proteins form trimer to reduce their non-polar interactions with surrounding water. Based on the obtained trimeric structure of Cry4Aa toxins, we propose that pore formation of Cry toxins may involve a 90 degrees -hairpin rotation during the insertion of their three alpha4-alpha5 hairpins into the membrane. This process may be mediated by water and ions.PACS Codes: 87.15.ap, 87.15.bk, 87.14.ep.
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Affiliation(s)
- Taveechai Taveecharoenkool
- Theoretical and Computational Biophysics Laboratory, Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand.
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15
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Soberón M, Pardo L, Muñóz-Garay C, Sánchez J, Gómez I, Porta H, Bravo A. Pore formation by Cry toxins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 677:127-42. [PMID: 20687486 DOI: 10.1007/978-1-4419-6327-7_11] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Bacillus thuringiensis (Bt) bacteria produce insecticidal Cry and Cyt proteins used in the biological control of different insect pests. In this review, we will focus on the 3d-Cry toxins that represent the biggest group of Cry proteins and also on Cyt toxins. The 3d-Cry toxins are pore-forming toxins that induce cell death by forming ionic pores into the membrane of the midgut epithelial cells in their target insect. The initial steps in the mode of action include ingestion of the protoxin, activation by midgut proteases to produce the toxin fragment and the interaction with the primary cadherin receptor. The interaction of the monomeric CrylA toxin with the cadherin receptor promotes an extra proteolytic cleavage, where helix alpha-1 of domain I is eliminated and the toxin oligomerization is induced, forming a structure of 250 kDa. The oligomeric structure binds to a secondary receptor, aminopeptidase N or alkaline phosphatase. The secondary receptor drives the toxin into detergent resistant membrane microdomains formingpores that cause osmotic shock, burst of the midgut cells and insect death. Regarding to Cyt toxins, these proteins have a synergistic effect on the toxicity of some Cry toxins. Cyt proteins are also proteolytic activated in the midgut lumen of their target, they bind to some phospholipids present in the mosquito midgut cells. The proposed mechanism of synergism between Cry and Cyt toxins is that Cyt1Aa function as a receptor for Cry toxins. The Cyt1A inserts into midgut epithelium membrane and exposes protein regions that are recognized by Cry11Aa. It was demonstrated that this interaction facilitates the oligomerization of Cry11Aa and also its pore formation activity.
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Affiliation(s)
- Mario Soberón
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Mexico City, Mexico
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16
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Anyatonwu G, Joseph SK. Surface accessibility and conformational changes in the N-terminal domain of type I inositol trisphosphate receptors: studies using cysteine substitution mutagenesis. J Biol Chem 2009; 284:8093-102. [PMID: 19141613 DOI: 10.1074/jbc.m806932200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To identify surface-accessible residues and monitor conformational changes of the type I inositol 1,4,5-trisphosphate receptor protein in membranes, we have introduced 10 cysteine substitutions into the N-terminal ligand-binding domain. The reactivity of these mutants with progressively larger maleimide-polyethylene glycol derivatives (MPEG) was measured using a gel shift assay of tryptic fragments. The results indicate that the mutations fall into four categories as follows: sites that are highly accessible based on reactivity with the largest 20-kDa MPEG (S2C); sites that are moderately accessible based on reactivity only with 5-kDa MPEG (S6C, S7C, A189C, and S277C); sites whose accessibility is markedly enhanced by Ca(2+) (S171C, S277C, and A575C); and sites that are inaccessible irrespective of incubation conditions (S217C, A245C, and S436C). The stimulation of accessibility induced by Ca(2+) at the S277C site occurred with an EC(50) of 0.8 mum and was mimicked by Sr(2+) but not Ba(2+). Inositol 1,4,5-trisphosphate alone did not affect reactivity of any of the mutants in the presence or absence of Ca(2+). The data are interpreted using crystal structures and EM reconstructions of the receptor. Our data identify N-terminal regions of the protein that become exposed upon Ca(2+) binding and suggest possible orientations of the suppressor and ligand-binding domains that have implications for the mechanism of gating of the channel.
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Affiliation(s)
- Georgia Anyatonwu
- Department of Pathology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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17
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Laflamme E, Badia A, Lafleur M, Schwartz JL, Laprade R. Atomic Force Microscopy Imaging of Bacillus thuringiensis Cry1 Toxins Interacting with Insect Midgut Apical Membranes. J Membr Biol 2008; 222:127-39. [DOI: 10.1007/s00232-008-9106-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Accepted: 03/23/2008] [Indexed: 11/28/2022]
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18
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Molecular dynamics studies of polyethylene oxide and polyethylene glycol: hydrodynamic radius and shape anisotropy. Biophys J 2008; 95:1590-9. [PMID: 18456821 DOI: 10.1529/biophysj.108.133025] [Citation(s) in RCA: 321] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length lambda = 3.7 A, in quantitative agreement with experimentally obtained values of 3.7 A for PEO and 3.8 A for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent upsilon relating the radius of gyration and molecular weight (R(g) proportional, variantM(w)(upsilon)) of PEO from the simulations equals 0.515 +/- 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R(h)obtained from diffusion measurements in solution. This explains the correspondence of R(h) and R(p), the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.
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19
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Torres J, Lin X, Boonserm P. A trimeric building block model for Cry toxins in vitro ion channel formation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:392-7. [PMID: 18047829 DOI: 10.1016/j.bbamem.2007.10.028] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2007] [Revised: 10/29/2007] [Accepted: 10/29/2007] [Indexed: 12/14/2022]
Abstract
The crystal (Cry) insecticidal toxins, or delta-endotoxins, are lethal to a wide variety of insect larvae, and are therefore very important in insect control. Toxicity has been explained by formation of transmembrane oligomeric pores or ion channels and, more recently, by the ability of the monomeric toxin to subvert cellular signaling pathways. The structure, topology, and precise role of the putative pore in toxicity are not known. However, in vitro biophysical studies suggest that helices alpha4 and alpha5 in domain I insert into the lipid bilayer as an alpha-helical hairpin. Mutagenesis studies have assigned an important role to alpha5 in maintaining oligomerization, and to alpha4 in channel formation. To detect the possible homo-oligomerizing tendencies of these two helices, we have used the evolutionary conservation data contained in sixteen Cry homologs in order to filter non-native interactions found during a global conformational search. No conserved homo-oligomer was found for alpha4, but a right handed trimeric alpha5 model was present in the simulations of all Cry sequences. We propose a model for Cry toxin oligomerization based on sequence analysis and available mutagenesis data.
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Affiliation(s)
- Jaume Torres
- School of Biological Sciences, Nanyang Technological University, 60, Nanyang Drive, Singapore 637551, Singapore.
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20
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Ounjai P, Unger VM, Sigworth FJ, Angsuthanasombat C. Two conformational states of the membrane-associated Bacillus thuringiensis Cry4Ba delta-endotoxin complex revealed by electron crystallography: implications for toxin-pore formation. Biochem Biophys Res Commun 2007; 361:890-5. [PMID: 17681273 PMCID: PMC2583932 DOI: 10.1016/j.bbrc.2007.07.086] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Accepted: 07/16/2007] [Indexed: 11/21/2022]
Abstract
The insecticidal nature of Cry delta-endotoxins produced by Bacillus thuringiensis is generally believed to be caused by their ability to form lytic pores in the midgut cell membrane of susceptible insect larvae. Here we have analyzed membrane-associated structures of the 65-kDa dipteran-active Cry4Ba toxin by electron crystallography. The membrane-associated toxin complex was crystallized in the presence of DMPC via detergent dialysis. Depending upon the charge of the adsorbed surface, 2D crystals of the oligomeric toxin complex have been captured in two distinct conformations. The projection maps of those crystals have been generated at 17A resolution. Both complexes appeared to be trimeric; as in one crystal form, its projection structure revealed a symmetrical pinwheel-like shape with virtually no depression in the middle of the complex. The other form revealed a propeller-like conformation displaying an obvious hole in the center region, presumably representing the toxin-induced pore. These crystallographic data thus demonstrate for the first time that the 65-kDa activated Cry4Ba toxin in association with lipid membranes could exist in at least two different trimeric conformations, conceivably implying the closed and open states of the pore.
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Affiliation(s)
- Puey Ounjai
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8024, USA
- Laboratory of Molecular Biophysics and Structural Biochemistry, Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170 Thailand
| | - Vinzenz M. Unger
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, P.O. Box 208024, New Haven, CT 06520-8024, USA
| | - Fred J. Sigworth
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8024, USA
| | - Chanan Angsuthanasombat
- Laboratory of Molecular Biophysics and Structural Biochemistry, Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170 Thailand
- Corresponding Author. Fax: +66-2-4419906, E-mail: (C. Angsuthanasombat)
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21
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Kirouac M, Vachon V, Fortier M, Trudel MC, Berteloot A, Schwartz JL, Laprade R. A mechanical force contributes to the "osmotic swelling" of brush-border membrane vesicles. Biophys J 2006; 91:3301-12. [PMID: 16905617 PMCID: PMC1614501 DOI: 10.1529/biophysj.106.088641] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Brush-border membrane vesicles and an osmotic swelling assay have been used extensively to monitor the pore-forming activity of Bacillus thuringiensis toxins. After a hypertonic shock, Manduca sexta midgut brush-border membrane vesicles shrink rapidly and reswell partially to a volume that depends on membrane permeability and toxin concentration rather than regaining their original volume as expected from theoretical models. Because efflux of buffer from the vesicles, as they shrink, could contribute to this phenomenon, vesicles were mixed with a hypertonic solution of the buffer with which they were loaded. Under these conditions, they are not expected to reswell, since the same solute is present on both sides of the membrane. Nevertheless, with several buffers, vesicles reswelled readily, an observation that demonstrates the involvement of an additional restoration force. Reswelling also occurred when, in the absence of toxin, the buffers were replaced by glucose, a solute that diffuses readily across the membrane, but did not occur with rat liver microsomes, despite their permeability to glucose. Unexpected swelling was also observed with rabbit jejunum brush-border membrane vesicles, suggesting that the cytoskeleton, present in brush-border membrane vesicles but absent from microsomes, could be responsible for the restoration force.
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Affiliation(s)
- Martin Kirouac
- Membrane Protein Research Group, University of Montreal, Montreal, Quebec, Canada
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22
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Molecular approaches for identification and construction of novel insecticidal genes for crop protection. World J Microbiol Biotechnol 2005. [DOI: 10.1007/s11274-005-9027-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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23
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Puntheeranurak T, Stroh C, Zhu R, Angsuthanasombat C, Hinterdorfer P. Structure and distribution of the Bacillus thuringiensis Cry4Ba toxin in lipid membranes. Ultramicroscopy 2005; 105:115-24. [PMID: 16125846 DOI: 10.1016/j.ultramic.2005.06.026] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2004] [Revised: 04/08/2005] [Indexed: 10/25/2022]
Abstract
Bacillus thuringiensis Cry delta-endotoxins cause death of susceptible insect larvae by forming lytic pores in the midgut epithelial cell membranes. The 65 kDa trypsin activated Cry4Ba toxin was previously shown to be capable of permeabilizing liposomes and forming ionic channels in receptor-free planar lipid bilayers. Here, magnetic ACmode (MACmode) atomic force microscopy (AFM) was used to characterize the lateral distribution and the native molecular structure of the Cry4Ba toxin in the membrane. Liposome fusion and the Langmuir-Blodgett technique were employed for supported lipid bilayer preparations. The toxin preferentially inserted in a self-assembled structure, rather than as a single monomeric molecule. In addition, the spontaneous insertion into receptor-free lipid bilayers lead to formation of characteristic pore-like structures with four-fold symmetry, suggesting that tetramers are the preferred oligomerization state of this toxin.
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Affiliation(s)
- Theeraporn Puntheeranurak
- Institute for Biophysics, Johannes Kepler University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
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24
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Ostroumova OS, Malev VV, Kaulin YA, Gurnev PA, Takemoto JY, Schagina LV. Voltage-dependent synchronization of gating of syringomycin E ion channels. FEBS Lett 2005; 579:5675-9. [PMID: 16219309 DOI: 10.1016/j.febslet.2005.08.087] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Revised: 08/26/2005] [Accepted: 08/26/2005] [Indexed: 11/30/2022]
Abstract
Antifungal lipodepsipeptide syringomycin E (SRE) forms two major conductive states in lipid bilayers: "small" and "large". Large SRE channels are cluster of several small ones, demonstrating synchronous opening and closure. To get insight into the mechanism of such synchronization we investigated how transmembrane potential, membrane surface charge, and ionic strength affect the number of small SRE channels synchronously functioning in the cluster. Here, we report that the large SRE channels can be presented as 3-8 simultaneously gating small channels. The increase in the absolute value of the transmembrane potential (from 50 to 200 mV) decreases the number of synchronously gated channels in the clusters. Voltage-dependence of channel synchronization was influenced by the ionic strength of the bathing solution, but not by membrane surface charge. We propose a mechanism for the voltage-dependent cluster behavior that involves a voltage-induced reorientation of lipid dipoles associated with the channel pores.
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Affiliation(s)
- O S Ostroumova
- Institute of Cytology of the Russian Academy of Sciences, St. Petersburg
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25
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Smith AW, Cámara-Artigas A, Brune DC, Allen JP. Implications of high-molecular-weight oligomers of the binary toxin from Bacillus sphaericus. J Invertebr Pathol 2005; 88:27-33. [PMID: 15707866 DOI: 10.1016/j.jip.2004.10.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2004] [Revised: 07/20/2004] [Accepted: 10/08/2004] [Indexed: 11/26/2022]
Abstract
The mosquito-larvicidal binary toxin produced by Bacillus sphaericus is composed of BinB and BinA, which have calculated molecular weights of 51.4 and 41.9 kDa, respectively. NaOH extracts of B. sphaericus spores were analyzed using SDS-PAGE. Stained gels showed bands with molecular weights corresponding to those of BinB and BinA as well as two additional bands at 110 and 125 kDa. The matrix-assisted laser desorption/ionization mass spectrum of the purified 110 and 125 kDa bands showed two peaks at 104,160 and 87,358 Da that are assigned to dimers of BinB and BinA, respectively. Mass spectral analysis of trypsin-digested 110 and 125 kDa bands showed peaks at 51,328, 43,523, 43,130, and 40,832 Da that assigned to undigested BinB, two forms of digested BinB and digested BinA, respectively. Dynamic light scattering studies showed a solution of the purified 110 and 125 kDa bands was comprised almost entirely (99.6% of total mass) of a particle with a hydrodynamic radius of 5.6+/-1.2 nm and a calculated molecular weight of 186+/-38 kDa. These data demonstrate that the binary toxin extracted from B. sphaericus spores can exist in solution as an oligomer containing two copies each of BinB and BinA.
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Affiliation(s)
- A W Smith
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA
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26
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Huffman DL, Bischof LJ, Griffitts JS, Aroian RV. Pore worms: using Caenorhabditis elegans to study how bacterial toxins interact with their target host. Int J Med Microbiol 2004; 293:599-607. [PMID: 15149037 DOI: 10.1078/1438-4221-00303] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The interaction of pathogenic bacteria with a target host is regulated both by bacterial virulence factors and by host components that either protect the host or that promote pathogenesis. The soil nematode Caenorhabditis elegans is a host for a number of bacterial pathogens, as briefly reviewed here. Bacillus thuringiensis (Bt) is a pathogenic bacteria that C. elegans is likely to encounter naturally in the soil. The pore-forming Crystal (Cry) toxins made by Bt are recognized as the dominant virulence factor in this host-pathogen interaction. Forward genetic screens for C. elegans mutants resistant to the Cry toxin, Cry5B, have identified a host carbohydrate structure that promotes pathogenesis. Data suggest this structure is likely to be a Cry5B receptor expressed in the host intestine. This finding is discussed in light of other carbohydrate receptors for bacterial toxins. To investigate host-toxin interactions on a global level, the response of C. elegans to the pore-forming Cry5B is also being investigated by gene transcription profiling (microarrays). These data are beginning to reveal a diverse intracellular response to toxin exposure. To put these investigations in perspective, host responses to other pore-forming toxins are discussed. Investigations with Cry5B in C. elegans show a promising beginning in helping to elucidate host-toxin and host-pathogen interactions.
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Affiliation(s)
- Danielle L Huffman
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA 92093-0349, USA
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27
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Rausell C, Muñoz-Garay C, Miranda-CassoLuengo R, Gómez I, Rudiño-Piñera E, Soberón M, Bravo A. Tryptophan spectroscopy studies and black lipid bilayer analysis indicate that the oligomeric structure of Cry1Ab toxin from Bacillus thuringiensis is the membrane-insertion intermediate. Biochemistry 2004; 43:166-74. [PMID: 14705942 DOI: 10.1021/bi035527d] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
During intoxication, the Cry protoxins must change from insoluble crystals into membrane-inserted toxins, which form ionic pores. Binding of Cry1A toxins to the cadherin receptor promotes the formation of a 250 kDa oligomer. In this work, we analyzed for the first time the structural changes presented by Cry1Ab toxin upon membrane insertion. Trp fluorescence of pure monomeric and oligomeric structures in solution and in a membrane-bound state was analyzed. Cry1Ab has nine Trp residues, seven of them in pore-forming domain I. Trp quenching analysis with iodide indicated that oligomerization caused a 27% reduction in the level of Trp exposed to the solvent. Most of the oligomeric structure (96%) inserts into the membrane as a function of the lipid:protein ratio, in contrast to the monomer (10%). Additionally, the membrane-associated oligomer presented a blue shift of 5 nm in lambda(max) of the emission spectrum, indicating a more hydrophobic environment for some Trp residues. In agreement with this, iodide was unable to quench the Trp of the membrane-bound oligomer, suggesting that a significant part of the protein may be buried in the membrane. Quenching analysis using brominated and spin-labeled phospholipids in the vesicles indicates that most of the Trp residues are located close to the membrane-water interface. Finally, ionic currents in black lipid bilayers revealed that the oligomeric structure has kinetics different from those of the monomer, producing stable channels with a high probability of being open in contrast to the monomer that exhibited unstable opening patterns. These data show that the oligomer, in contrast to the monomer, is able to interact efficiently with phospholipid membranes forming stable pores.
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Affiliation(s)
- Carolina Rausell
- Departamento de Microbiología Molecular and Departamento de Reconocimiento Molecular y Bioestructura, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo postal 510-3, Cuernavaca 62250, Morelos, Mexico
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