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Tucker SK, McHugh RE, Roe AJ. One problem, multiple potential targets: Where are we now in the development of small molecule inhibitors against Shiga toxin? Cell Signal 2024; 121:111253. [PMID: 38852937 DOI: 10.1016/j.cellsig.2024.111253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2024] [Revised: 06/04/2024] [Accepted: 06/06/2024] [Indexed: 06/11/2024]
Abstract
Shiga toxin-producing Escherichia coli (STEC) are a group of enteric pathogens which carry phage-encoded Shiga toxins (Stx). STEC infections begin with severe abdominal pain and non-bloody diarrhoea, which can progress to bloody diarrhoea after approximately 4-days post-infection. In high-risk groups such as children and the elderly, patients may develop haemolytic uremic syndrome (HUS). HUS is characterised by microangiopathic haemolytic anaemia, thrombocytopenia, and in severe disease acute renal failure. Traditional antibiotics have been linked with increased toxin production due to the activation of recA-mediated bacterial stress response, resulting in poorer patient outcomes. Therefore, treatment relies on supportive therapies. Antivirulence strategies have been explored as an alternative treatment for bacterial infections and blockers of virulence factors such as the Type III Secretion System. Recent improvements in the mechanistic understanding of the Stx pathway have led to the design of inhibitors to disrupt the pathway, leading to toxin-mediated ribosome damage. However, compounds have yet to progress beyond Phase III clinical trials successfully. This review explores the progress in developing small molecule inhibitors by collating lead compounds derived from in-silico and experimental approaches.
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Affiliation(s)
- Samantha K Tucker
- School of Infection and Immunity, University of Glasgow, Glasgow G12 8TA, United Kingdom
| | - Rebecca E McHugh
- School of Infection and Immunity, University of Glasgow, Glasgow G12 8TA, United Kingdom
| | - Andrew J Roe
- School of Infection and Immunity, University of Glasgow, Glasgow G12 8TA, United Kingdom.
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2
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Czajka TF, Vance DJ, Davis S, Rudolph MJ, Mantis NJ. Single-domain antibodies neutralize ricin toxin intracellularly by blocking access to ribosomal P-stalk proteins. J Biol Chem 2022; 298:101742. [PMID: 35182523 PMCID: PMC8941211 DOI: 10.1016/j.jbc.2022.101742] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Revised: 02/10/2022] [Accepted: 02/14/2022] [Indexed: 12/27/2022] Open
Abstract
During ricin intoxication in mammalian cells, ricin's enzymatic (RTA) and binding (RTB) subunits disassociate in the endoplasmic reticulum. RTA is then translocated into the cytoplasm where, by virtue of its ability to depurinate a conserved residue within the sarcin-ricin loop (SRL) of 28S rRNA, it functions as a ribosome-inactivating protein. It has been proposed that recruitment of RTA to the SRL is facilitated by ribosomal P-stalk proteins, whose C-terminal domains interact with a cavity on RTA normally masked by RTB; however, evidence that this interaction is critical for RTA activity within cells is lacking. Here, we characterized a collection of single-domain antibodies (VHHs) whose epitopes overlap with the P-stalk binding pocket on RTA. The crystal structures of three such VHHs (V9E1, V9F9, and V9B2) in complex with RTA revealed not only occlusion of the ribosomal P-stalk binding pocket but also structural mimicry of C-terminal domain peptides by complementarity-determining region 3. In vitro assays confirmed that these VHHs block RTA-P-stalk peptide interactions and protect ribosomes from depurination. Moreover, when expressed as "intrabodies," these VHHs rendered cells resistant to ricin intoxication. One VHH (V9F6), whose epitope was structurally determined to be immediately adjacent to the P-stalk binding pocket, was unable to neutralize ricin within cells or protect ribosomes from RTA in vitro. These findings are consistent with the recruitment of RTA to the SRL by ribosomal P-stalk proteins as a requisite event in ricin-induced ribosome inactivation.
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Affiliation(s)
- Timothy F Czajka
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA
| | - David J Vance
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA; Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Simon Davis
- New York Structural Biology Center, New York, New York, USA
| | | | - Nicholas J Mantis
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA; Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, New York, USA.
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Gupta N, Noël R, Goudet A, Hinsinger K, Michau A, Pons V, Abdelkafi H, Secher T, Shima A, Shtanko O, Sakurai Y, Cojean S, Pomel S, Liévin-Le Moal V, Leignel V, Herweg JA, Fischer A, Johannes L, Harrison K, Beard PM, Clayette P, Le Grand R, Rayner JO, Rudel T, Vacus J, Loiseau PM, Davey RA, Oswald E, Cintrat JC, Barbier J, Gillet D. Inhibitors of retrograde trafficking active against ricin and Shiga toxins also protect cells from several viruses, Leishmania and Chlamydiales. Chem Biol Interact 2016; 267:96-103. [PMID: 27712998 DOI: 10.1016/j.cbi.2016.10.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 08/09/2016] [Accepted: 10/03/2016] [Indexed: 11/25/2022]
Abstract
Medical countermeasures to treat biothreat agent infections require broad-spectrum therapeutics that do not induce agent resistance. A cell-based high-throughput screen (HTS) against ricin toxin combined with hit optimization allowed selection of a family of compounds that meet these requirements. The hit compound Retro-2 and its derivatives have been demonstrated to be safe in vivo in mice even at high doses. Moreover, Retro-2 is an inhibitor of retrograde transport that affects syntaxin-5-dependent toxins and pathogens. As a consequence, it has a broad-spectrum activity that has been demonstrated both in vitro and in vivo against ricin, Shiga toxin-producing O104:H4 entero-hemorrhagic E. coli and Leishmania sp. and in vitro against Ebola, Marburg and poxviruses and Chlamydiales. An effect is anticipated on other toxins or pathogens that use retrograde trafficking and syntaxin-5. Since Retro-2 targets cell components of the host and not directly the pathogen, no selection of resistant pathogens is expected. These lead compounds need now to be developed as drugs for human use.
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Affiliation(s)
- Neetu Gupta
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Romain Noël
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Amélie Goudet
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Karen Hinsinger
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Aurélien Michau
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Valérie Pons
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Hajer Abdelkafi
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | | | | | - Olena Shtanko
- Texas Biomedical Research Institute, San Antonio, TX, USA
| | | | - Sandrine Cojean
- Antiparasitic Chemotherapy, UMR 8076, CNRS BioCIS, LabEx LERMIT, Université Paris-Sud, Université Paris-Saclay, F-92290, Chatenay-Malabry, France
| | - Sébastien Pomel
- Antiparasitic Chemotherapy, UMR 8076, CNRS BioCIS, LabEx LERMIT, Université Paris-Sud, Université Paris-Saclay, F-92290, Chatenay-Malabry, France
| | - Vanessa Liévin-Le Moal
- Antiparasitic Chemotherapy, UMR 8076, CNRS BioCIS, LabEx LERMIT, Université Paris-Sud, Université Paris-Saclay, F-92290, Chatenay-Malabry, France
| | - Véronique Leignel
- DRUGABILIS (French Research Performer SME), F-92290, Chatenay-Malabry, France
| | - Jo-Ana Herweg
- University of Würzburg, Biocenter, Chair of Microbiology, Am Hubland, D-97074, Würzburg, Germany
| | - Annette Fischer
- University of Würzburg, Biocenter, Chair of Microbiology, Am Hubland, D-97074, Würzburg, Germany
| | - Ludger Johannes
- Institut Curie, PSL Research University, Endocytic Trafficking and Therapeutic Delivery Group, 26 rue d'Ulm, F-75248, Paris Cedex 05, France; CNRS, UMR3666, F-75005, Paris, France; INSERM, U1143, F-75005, Paris, France
| | - Kate Harrison
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Midlothian, EH25 9RG, United Kingdom
| | - Philippa M Beard
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Midlothian, EH25 9RG, United Kingdom; The Pirbright Institute, Ash Rd, Pirbright, Surrey GH24 0NF, United Kingdom
| | - Pascal Clayette
- ImmunoPharmacology and Biosafety Laboratory, BERTIN Pharma, CEA, F-92265, Fontenay-aux-Roses, France
| | - Roger Le Grand
- Institute of Emerging Diseases and Innovative Therapies, CEA, U1184, Immunology of Viral Infections and Autoimmune Diseases, Infectious Disease Models and Innovative Therapies Infrastructure, F-92265, Fontenay-aux-Roses, France; INSERM, U1184, F-94276, Le Kremlin-Bicêtre, France; University of Paris South, U1184, F-92265, Fontenay-aux-Roses, France; Vaccine Research Institute, Henri Mondor Hospital, F-94010, Créteil, France
| | - Jonathan O Rayner
- Infectious Disease Research, Southern Research, 2000 Ninth Avenue South, Birmingham, AL 35205, USA
| | - Thomas Rudel
- University of Würzburg, Biocenter, Chair of Microbiology, Am Hubland, D-97074, Würzburg, Germany
| | - Joël Vacus
- DRUGABILIS (French Research Performer SME), F-92290, Chatenay-Malabry, France
| | - Philippe M Loiseau
- Antiparasitic Chemotherapy, UMR 8076, CNRS BioCIS, LabEx LERMIT, Université Paris-Sud, Université Paris-Saclay, F-92290, Chatenay-Malabry, France
| | - Robert A Davey
- Texas Biomedical Research Institute, San Antonio, TX, USA
| | | | - Jean-Christophe Cintrat
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Julien Barbier
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France
| | - Daniel Gillet
- Institute of Biology and Technology of Saclay (IBITECS), CEA, LabEx LERMIT, Université Paris-Saclay, F-91191, Gif Sur Yvette, France.
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Kumar RB, Suresh MX. A computational perspective of molecular interactions through virtual screening, pharmacokinetic and dynamic prediction on ribosome toxin A chain and inhibitors of Ricinus communis. Pharmacognosy Res 2012; 4:2-10. [PMID: 22224054 PMCID: PMC3250034 DOI: 10.4103/0974-8490.91027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2011] [Revised: 09/04/2011] [Accepted: 12/22/2011] [Indexed: 11/28/2022] Open
Abstract
Background: Ricin is considered to be one of the most deadly toxins and gained its favor as a bioweapon that has a serious social and biological impact, due to its widespread nature and abundant availability. The hazardous effects of this toxin in human being are seen in almost all parts of the organ system. The severe consequences of the toxin necessitate the need for developing potential inhibitors that can effectively block its interaction with the host system. Materials and Methods: In order to identify potential inhibitors that can effectively block ricin, we employed various computational approaches. In this work, we computationally screened and analyzed 66 analogs and further tested their ADME/T profiles. From the kinetic and toxicity studies we selected six analogs that possessed appropriate pharmacokinetic and dynamic property. We have also performed a computational docking of these analogs with the target. Results: On the basis of the dock scores and hydrogen bond interactions we have identified analog 64 to be the best interacting molecule. Molecule 64 seems to have stable interaction with the residues Tyr80, Arg180, and Val81. The pharmacophore feature that describes the key functional features of a molecule was also studied and presented. Conclusion: The pharmacophore features of the drugs provided suggests the key functional groups that can aid in the design and synthesis of more potential inhibitors.
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Affiliation(s)
- R Barani Kumar
- Department of Bioinformatics, Sathyabama University, Chennai, Tamil Nadu, India
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5
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Inhibitors of the cellular trafficking of ricin. Toxins (Basel) 2012; 4:15-27. [PMID: 22347620 PMCID: PMC3277095 DOI: 10.3390/toxins4010015] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 12/22/2011] [Accepted: 12/23/2011] [Indexed: 12/26/2022] Open
Abstract
Throughout the last decade, efforts to identify and develop effective inhibitors of the ricin toxin have focused on targeting its N-glycosidase activity. Alternatively, molecules disrupting intracellular trafficking have been shown to block ricin toxicity. Several research teams have recently developed high-throughput phenotypic screens for small molecules acting on the intracellular targets required for entry of ricin into cells. These screens have identified inhibitory compounds that can protect cells, and sometimes even animals against ricin. We review these newly discovered cellular inhibitors of ricin intoxication, discuss the advantages and drawbacks of chemical-genetics approaches, and address the issues to be resolved so that the therapeutic development of these small-molecule compounds can progress.
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Srivastava M, Gupta SK, Abhilash PC, Singh N. Structure prediction and binding sites analysis of curcin protein of Jatropha curcas using computational approaches. J Mol Model 2011; 18:2971-9. [PMID: 22146985 DOI: 10.1007/s00894-011-1320-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Accepted: 11/22/2011] [Indexed: 11/29/2022]
Abstract
Ribosome inactivating proteins (RIPs) are defense proteins in a number of higher-plant species that are directly targeted toward herbivores. Jatropha curcas is one of the biodiesel plants having RIPs. The Jatropha seed meal, after extraction of oil, is rich in curcin, a highly toxic RIP similar to ricin, which makes it unsuitable for animal feed. Although the toxicity of curcin is well documented in the literature, the detailed toxic properties and the 3D structure of curcin has not been determined by X-ray crystallography, NMR spectroscopy or any in silico techniques to date. In this pursuit, the structure of curcin was modeled by a composite approach of 3D structure prediction using threading and ab initio modeling. Assessment of model quality was assessed by methods which include Ramachandran plot analysis and Qmean score estimation. Further, we applied the protein-ligand docking approach to identify the r-RNA binding residue of curcin. The present work provides the first structural insight into the binding mode of r-RNA adenine to the curcin protein and forms the basis for designing future inhibitors of curcin. Cloning of a future peptide inhibitor within J. curcas can produce non-toxic varieties of J. curcas, which would make the seed-cake suitable as animal feed without curcin detoxification.
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Affiliation(s)
- Mugdha Srivastava
- Eco-Auditing Laboratory, National Botanical Research Institute, CSIR, Lucknow, 226001 Uttar Pradesh, India.
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7
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Detection of ricin using a carbon nanofiber based biosensor. Biosens Bioelectron 2011; 28:428-33. [DOI: 10.1016/j.bios.2011.07.061] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2011] [Revised: 07/11/2011] [Accepted: 07/25/2011] [Indexed: 11/20/2022]
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8
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Duncton MAJ. Minisci reactions: Versatile CH-functionalizations for medicinal chemists. MEDCHEMCOMM 2011. [DOI: 10.1039/c1md00134e] [Citation(s) in RCA: 426] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Wahome PG, Robertus JD, Mantis NJ. Small-molecule inhibitors of ricin and Shiga toxins. Curr Top Microbiol Immunol 2011; 357:179-207. [PMID: 22006183 DOI: 10.1007/82_2011_177] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
This review summarizes the successes and continuing challenges associated with the identification of small-molecule inhibitors of ricin and Shiga toxins, members of the RNA N-glycosidase family of toxins that irreversibly inactivate eukaryotic ribosomes through the depurination of a conserved adenosine residue within the sarcin-ricin loop (SRL) of 28S rRNA. Virtual screening of chemical libraries has led to the identification of at least three broad classes of small molecules that bind in or near the toxin's active sites and thereby interfere with RNA N-glycosidase activity. Rational design is being used to improve the specific activity and solubility of a number of these compounds. High-throughput cell-based assays have also led to the identification of small molecules that partially, or in some cases, completely protect cells from ricin- and Shiga-toxin-induced death. A number of these recently identified compounds act on cellular proteins associated with intracellular trafficking or pro-inflammatory/cell death pathways, and one was reported to be sufficient to protect mice in a ricin challenge model.
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Affiliation(s)
- Paul G Wahome
- Division of Infectious Disease, Wadsworth Center New York State Department of Health, Albany, NY 12208, USA
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10
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Wahome PG, Bai Y, Neal LM, Robertus JD, Mantis NJ. Identification of small-molecule inhibitors of ricin and shiga toxin using a cell-based high-throughput screen. Toxicon 2010; 56:313-23. [PMID: 20350563 PMCID: PMC2902711 DOI: 10.1016/j.toxicon.2010.03.016] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2010] [Revised: 03/18/2010] [Accepted: 03/19/2010] [Indexed: 10/19/2022]
Abstract
The Category B agents, ricin and shiga toxin (Stx), are RNA N-glycosidases that target a highly conserved adenine residue within the sarcin-ricin loop of eukaryotic 28S ribosomal RNA. In an effort to identify small-molecule inhibitors of these toxins that could serve as lead compounds for potential therapeutics, we have developed a simple Vero cell-based high-throughput cytotoxicity assay and have used it to screen approximately 81,300 compounds in 17 commercially available chemical libraries. This initial screen identified approximately 300 compounds with weak (>or=30 to <50%), moderate (>or=50 to <80%), or strong (>or=80%) ricin inhibitory activity. Secondary analysis of 244 of these original "hits" was performed, and 20 compounds that were capable of reducing ricin cytotoxicity by >50% were chosen for further study. Four compounds demonstrated significant dose-dependent ricin inhibitory activity in the Vero cell-based assay, with 50% effective inhibitory concentration (EC(50)) values ranging from 25 to 60microM. The same 20 compounds were tested in parallel for the ability to inhibit ricin's and Stx1's enzymatic activities in an in vitro translation reaction. Three of the 20 compounds, including the most effective compound in the cell-based assay, had discernible anti-toxin activity. One compound in particular, 4-fluorophenyl methyl 2-(furan-2-yl)quinoline-4-carboxylate ("compound 8"), had 50% inhibitory concentration (IC(50)) of 30microM, a value indicating >10-fold higher potency than is the case for previously described ricin-Stx1 inhibitors. Computer modeling predicted that compound 8 is capable of docking within the ricin active site. In conclusion, we have used a simple high-throughput cell-based method to identify several new small-molecule inhibitors of ricin and Stx.
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Affiliation(s)
- Paul G. Wahome
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
| | - Yan Bai
- Department of Chemistry and Biochemistry, University of Texas, Austin, Texas 78712, USA
| | - Lori M. Neal
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
| | - Jon D. Robertus
- Department of Chemistry and Biochemistry, University of Texas, Austin, Texas 78712, USA
| | - Nicholas J. Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
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Carra JH, McHugh CA, Mulligan S, Machiesky LM, Soares AS, Millard CB. Fragment-based identification of determinants of conformational and spectroscopic change at the ricin active site. BMC STRUCTURAL BIOLOGY 2007; 7:72. [PMID: 17986339 PMCID: PMC2194779 DOI: 10.1186/1472-6807-7-72] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2007] [Accepted: 11/06/2007] [Indexed: 12/05/2022]
Abstract
Background Ricin is a potent toxin and known bioterrorism threat with no available antidote. The ricin A-chain (RTA) acts enzymatically to cleave a specific adenine base from ribosomal RNA, thereby blocking translation. To understand better the relationship between ligand binding and RTA active site conformational change, we used a fragment-based approach to find a minimal set of bonding interactions able to induce rearrangements in critical side-chain positions. Results We found that the smallest ligand stabilizing an open conformer of the RTA active site pocket was an amide group, bound weakly by only a few hydrogen bonds to the protein. Complexes with small amide-containing molecules also revealed a switch in geometry from a parallel towards a splayed arrangement of an arginine-tryptophan cation-pi interaction that was associated with an increase and red-shift in tryptophan fluorescence upon ligand binding. Using the observed fluorescence signal, we determined the thermodynamic changes of adenine binding to the RTA active site, as well as the site-specific binding of urea. Urea binding had a favorable enthalpy change and unfavorable entropy change, with a ΔH of -13 ± 2 kJ/mol and a ΔS of -0.04 ± 0.01 kJ/(K*mol). The side-chain position of residue Tyr80 in a complex with adenine was found not to involve as large an overlap of rings with the purine as previously considered, suggesting a smaller role for aromatic stacking at the RTA active site. Conclusion We found that amide ligands can bind weakly but specifically to the ricin active site, producing significant shifts in positions of the critical active site residues Arg180 and Tyr80. These results indicate that fragment-based drug discovery methods are capable of identifying minimal bonding determinants of active-site side-chain rearrangements and the mechanistic origins of spectroscopic shifts. Our results suggest that tryptophan fluorescence provides a sensitive probe for the geometric relationship of arginine-tryptophan pairs, which often have significant roles in protein function. Using the unusual characteristics of the RTA system, we measured the still controversial thermodynamic changes of site-specific urea binding to a protein, results that are relevant to understanding the physical mechanisms of protein denaturation.
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Affiliation(s)
- John H Carra
- United States Army Medical Research Institute of Infectious Diseases, 1425 Porter St,, Fort Detrick, MD 21702, USA.
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12
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Marsden CJ, Smith DC, Roberts LM, Lord JM. Ricin: current understanding and prospects for an antiricin vaccine. Expert Rev Vaccines 2006; 4:229-37. [PMID: 15889996 DOI: 10.1586/14760584.4.2.229] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Ricin is a potent cytotoxin that can be rapidly internalized into mammalian cells leading to cell death. The ease in obtaining the toxin and its deadly nature combine to implicate ricin as a convenient agent for bioterrorism. Research into the mechanism of toxicity, as well as strategies for treatment and protection from the toxin has been widely undertaken for a number of years. This article reviews the current understanding of the mechanism of action of the toxin, the clinical effects of ricin intoxication and how these relate to current and continuing prospects for vaccine development.
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Affiliation(s)
- Catherine J Marsden
- Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, UK.
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13
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Dawson RM, Alderton MR, Wells D, Hartley PG. Monovalent and polyvalent carbohydrate inhibitors of ricin binding to a model of the cell-surface receptor. J Appl Toxicol 2006; 26:247-52. [PMID: 16489581 DOI: 10.1002/jat.1136] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A selection of galactose and lactose analogues was evaluated for their potency in inhibiting the binding of ricin to immobilised asialofetuin, which is a model of the cell-surface receptor for ricin. The aim was to identify compounds that could be used as antagonists of ricin toxicity in vivo, and as more selective, and therefore safer, antitoxins. Although one of these analogues had been identified by molecular modelling in a previous study as a potentially potent inhibitor, it and the other carbohydrates studied were less effective than galactose and lactose themselves (I(50) = 1.39 and 0.74 mM, respectively). In an attempt to increase the potency of carbohydrate-based inhibitors, galactose was coupled to the surface of dendrimers. No synergistic interactions were observed from this multivalent approach. Encouraging results, however, were obtained with a self-assembled lyotropic mesophase gel containing novel synthetic galactose-based surfactants, which was able to sequester ricin from aqueous solution in a 2-phase system.
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Affiliation(s)
- R M Dawson
- Platforms Sciences Laboratory, Defence Science and Technology Organisation, Melbourne VIC 3001, Australia.
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14
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Mishra V, Bilgrami S, Sharma RS, Kaur P, Yadav S, Krauspenhaar R, Betzel C, Voelter W, Babu CR, Singh TP. Crystal Structure of Himalayan Mistletoe Ribosome-inactivating Protein Reveals the Presence of a Natural Inhibitor and a New Functionally Active Sugar-binding Site. J Biol Chem 2005; 280:20712-21. [PMID: 15774467 DOI: 10.1074/jbc.m500735200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ribosome-inactivating proteins (RIPs) are toxins involved in plant defense. How the plant prevents autotoxicity is not yet fully understood. The present study is the first structural evidence of a naturally inhibited form of RIP from a plant. Himalayan mistletoe RIP (HmRIP) was purified from Viscum album leaves and crystallized with lactose. The structure was determined by the molecular replacement method and refined at 2.8-A resolution. The crystal structure revealed the presence of high quality non-protein electron density at the active site, into which a pteridine derivative (2-amino 4-isopropyl 6-carboxyl pteridine) was modeled. The carboxyl group of the ligand binds strongly with the key active site residue Arg(162), nullifies the positive charge required for catalysis, and thereby acts as a natural inhibitor. Lectin subunits of RIPs have two active sugar-binding sites present in 1alpha- and 2gamma-subdomains. A third functionally active site has been identified in the 1beta-subdomain of HmRIP. The 1beta-site is active despite the absence of conserved polar sugar-binding residues. Loss of these residues is compensated by the following: (i) the presence of an extended site where the penultimate sugar also interacts with the protein; (ii) the interactions of galactose with the protein main chain carbonyl and amide nitrogen atoms; (iii) the presence of a well defined pocket encircled by four walls; and (iv) a favorable stacking of the galactose ring with Tyr(66) besides the conserved Phe(75). The mode of sugar binding is also distinct at the 1alpha and 2gamma sugar-binding sites.
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Affiliation(s)
- Vandana Mishra
- Department of Biophysics, All India Institute of Medical Sciences, New Delhi 110 029, India
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Hesselberth JR, Miller D, Robertus J, Ellington AD. In vitro selection of RNA molecules that inhibit the activity of ricin A-chain. J Biol Chem 2000; 275:4937-42. [PMID: 10671531 DOI: 10.1074/jbc.275.7.4937] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cytotoxin ricin disables translation by depurinating a conserved site in eukaryotic rRNA. In vitro selection has been used to generate RNA ligands (aptamers) specific for the catalytic ricin A-chain (RTA). The anti-RTA aptamers bear no resemblance to the normal RTA substrate, the sarcin-ricin loop (SRL), and were not depurinated by RTA. An initial 80-nucleotide RNA ligand was minimized to a 31-nucleotide aptamer that contained all sequences and structures necessary for interacting with RTA. This minimal RNA formed high affinity complexes with RTA (K(d) = 7.3 nM) which could compete directly with the SRL for binding to RTA. The aptamer inhibited RTA depurination of the SRL and could partially protect translation from RTA inhibition. The IC(50) of the aptamer for RTA in an in vitro translation assay is 100 nM, roughly 3 orders of magnitude lower than a small molecule inhibitor of ricin, pteroic acid, and 2 orders of magnitude lower than the best known RNA inhibitor. The novel anti-RTA aptamers may find application as diagnostic reagents for a potential biological warfare agent and hold promise as scaffolds for the development of strong ricin inhibitors.
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Affiliation(s)
- J R Hesselberth
- Department of Chemistry and Biochemistry, University of Texas, Austin, Texas 78712, USA
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16
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Li HG, Xu SZ, Wu S, Yan L, Li JH, Wong RN, Shi QL, Dong YC. Role of Arg163 in the N-glycosidase activity of neo-trichosanthin. PROTEIN ENGINEERING 1999; 12:999-1004. [PMID: 10585506 DOI: 10.1093/protein/12.11.999] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Three mutant crystals of neo-trichosanthin (n-TCS), R163K, R163H and R163Q, were obtained by the hanging drop vapor diffusion method. Structure determination indicated that there are no significant differences between the mutants and n-TCS except in the active pocket. All of them were also soaked in sodium citrate buffer (pH 4. 5) containing 20% KCl and 10 mg/ml AMP. Structure determination suggests that in the active pocket of the crystals of R163K and R163H, parallel to the aromatic ring of Tyr70, each mutant possesses an adenine. The relationship between structure and function is discussed. Biochemical analysis reveals that the mutants R163K and R163H have N-glycosidase activity, while R163Q does not. This suggests that R163 is a crucial residue for the enzyme activity of n-TCS, and its role is providing proton.
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Affiliation(s)
- H G Li
- Department of Protein Engineering, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101 and Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China
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17
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Agapov II, Tonevitsky AG, Moysenovich MM, Maluchenko NV, Weyhenmeyer R, Kirpichnikov MP. Mistletoe lectin dissociates into catalytic and binding subunits before translocation across the membrane to the cytoplasm. FEBS Lett 1999; 452:211-4. [PMID: 10386592 DOI: 10.1016/s0014-5793(99)00639-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Hybridomas producing monoclonal antibodies (mAbs) against the mistletoe lectin A-chain (MLA) were obtained to investigate the intracellular routing and translocation of ribosome-inactivating proteins. Anti-MLA mAb MNA5 did not bind the holotoxin but interacted with isolated MLA. This epitope was not recognized upon MLA denaturation or conjugation of MLA with the ricin binding subunit (RTB). Furthermore, the mAbs did not appreciably react with a panel of MLA synthetic octapeptides linked to the surface of polyethylene pins. A study of the cytotoxicity of mistletoe lectin, ricin, and chimeric toxin MLA/RTB for the hybridomas revealed that interchain disulfide bond reduction and subunit dissociation are required for cytotoxic activity of mistletoe lectin.
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Affiliation(s)
- I I Agapov
- State Research Center GNIIgenetika, Moscow, Russia
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