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Bhattacharya S, Dahmane T, Goger MJ, Rudolph MJ, Tumer NE. 1H, 13C, and 15N backbone and methyl group resonance assignments of ricin toxin A subunit. BIOMOLECULAR NMR ASSIGNMENTS 2024; 18:85-91. [PMID: 38642265 PMCID: PMC11081922 DOI: 10.1007/s12104-024-10172-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 04/01/2024] [Indexed: 04/22/2024]
Abstract
Ricin is a potent plant toxin that targets the eukaryotic ribosome by depurinating an adenine from the sarcin-ricin loop (SRL), a highly conserved stem-loop of the rRNA. As a category-B agent for bioterrorism it is a prime target for therapeutic intervention with antibodies and enzyme blocking inhibitors since no effective therapy exists for ricin. Ricin toxin A subunit (RTA) depurinates the SRL by binding to the P-stalk proteins at a remote site. Stimulation of the N-glycosidase activity of RTA by the P-stalk proteins has been studied extensively by biochemical methods and by X-ray crystallography. The current understanding of RTA's depurination mechanism relies exclusively on X-ray structures of the enzyme in the free state and complexed with transition state analogues. To date we have sparse evidence of conformational dynamics and allosteric regulation of RTA activity that can be exploited in the rational design of inhibitors. Thus, our primary goal here is to apply solution NMR techniques to probe the residue specific structural and dynamic coupling active in RTA as a prerequisite to understand the functional implications of an allosteric network. In this report we present de novo sequence specific amide and sidechain methyl chemical shift assignments of the 267 residue RTA in the free state and in complex with an 11-residue peptide (P11) representing the identical C-terminal sequence of the ribosomal P-stalk proteins. These assignments will facilitate future studies detailing the propagation of binding induced conformational changes in RTA complexed with inhibitors, antibodies, and biologically relevant targets.
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Affiliation(s)
- Shibani Bhattacharya
- New York Structural Biology Center, 89 Convent Avenue, New York, NY, 10027, USA.
| | - Tassadite Dahmane
- New York Structural Biology Center, 89 Convent Avenue, New York, NY, 10027, USA
| | - Michael J Goger
- New York Structural Biology Center, 89 Convent Avenue, New York, NY, 10027, USA
| | - Michael J Rudolph
- New York Structural Biology Center, 89 Convent Avenue, New York, NY, 10027, USA
| | - Nilgun E Tumer
- Department of Plant Biology and Pathology, School of Environmental and Biological Sciences, Rutgers University, 59 Dudley Road, New Brunswick, NJ, 08901-8520, USA
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2
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França TCC, Botelho FD, Drummond ML, LaPlante SR. Theoretical Investigation of Repurposed Drugs Potentially Capable of Binding to the Catalytic Site and the Secondary Binding Pocket of Subunit A of Ricin. ACS OMEGA 2022; 7:32805-32815. [PMID: 36120038 PMCID: PMC9476511 DOI: 10.1021/acsomega.2c04819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 08/16/2022] [Indexed: 06/15/2023]
Abstract
Recently, we reported a library of 82 compounds, selected from different databanks through virtual screening and docking studies, and pointed to 6 among them as potential repurposed dual binders to both the catalytic site and the secondary binding pockets of subunit A of ricin (RTA). Here, we report additional molecular modeling studies of an extended list of compounds from the original library. Rounds of flexible docking followed by molecular dynamics simulations and further rounds of MM-PBSA calculations using a more robust protocol, enabled a better investigation of the interactions of these compounds inside RTA, the elucidation of their dynamical behaviors, and updating the list of the most important residues for the ligand binding. Four compounds were pointed as potential repurposed ricin inhibitors that are worth being experimentally investigated.
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Affiliation(s)
- Tanos C. C. França
- Université
de Québec, INRS—Centre Armand-Frappier Santé
Biotechnologie, Laval, Quebec H7V 1B7, Canada
- Laboratory
of Molecular Modeling Applied to Chemical and Biological Defense, Military Institute of Engineering, Rio de Janeiro 22290-270, Brazil
- Department
of Chemistry, Faculty of Science, University
of Hradec Kralove, Rokitanskeho
62, Hradec Kralove 50003, Czech Republic
| | - Fernanda D. Botelho
- Laboratory
of Molecular Modeling Applied to Chemical and Biological Defense, Military Institute of Engineering, Rio de Janeiro 22290-270, Brazil
| | | | - Steven R. LaPlante
- Université
de Québec, INRS—Centre Armand-Frappier Santé
Biotechnologie, Laval, Quebec H7V 1B7, Canada
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Pillai CA, Manickam G, Thirunavukkarasu N, Pillai SP, Morse SA, Avila JR, Hodge DR, Anderson K, Sharma S. Evaluation of an Electrochemiluminescence Assay for the Rapid Detection of Abrin Toxin. Health Secur 2021; 19:431-441. [PMID: 34227874 DOI: 10.1089/hs.2020.0102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In this article, we detail a comprehensive laboratory evaluation of an immunoassay for the rapid detection of abrin using the Meso Scale Diagnostics Sector PR2 Model 1800. For the assay evaluation, we used inclusivity and exclusivity panels comprised of extracts of 11 Abrus precatorius cultivars and 35 near-neighbor plants, 65 lectins, 26 white powders, 11 closely related toxins and proteins, and a pool of 30 BioWatch filter extracts. The results show that the Meso Scale Diagnostics abrin detection assay exhibits good sensitivity and specificity with a limit of detection of 4 ng/mL. However, the dynamic range of the assay for the quantitation of abrin was limited. We observed a hook effect at higher abrin concentrations, which can lead to potential false negative results. A modification of the assay protocol that incorporates extra wash steps can decrease the hook effect and the potential for false negative results.
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Affiliation(s)
- Christine A Pillai
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Gowri Manickam
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Nagarajan Thirunavukkarasu
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Segaran P Pillai
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Stephen A Morse
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Julie R Avila
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - David R Hodge
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Kevin Anderson
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
| | - Shashi Sharma
- Christine A. Pillai and Gowri Manickam, PhD, are ORISE Fellow Research Scientists; Nagarajan Thirunavukkarasu, PhD, is a Microbiologist; and Shashi Sharma, PhD, is Principal Investigator; all at the Center for Food Safety and Applied Nutrition, Molecular Methods Development Branch, Division of Microbiology, Office of Regulatory Science, US Food and Drug Administration, College Park, MD. Segaran P. Pillai, PhD, FAAM, SM(NRCM), SM(ASCP), is Director, Office of Laboratory Science and Safety, Office of the Commissioner, US Food and Drug Administration, Silver Spring, MD. Stephen A. Morse, PhD, MSPH, is Senior Advisor, CDC Division of Select Agents and Toxins, IHRC, Inc., Atlanta, GA. Julie R. Avila, MS, is Scientific Associate, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA. David R. Hodge, PhD, and Kevin Anderson, PhD, are Program Managers; both in the Science and Technology Directorate, US Department of Homeland Security, Washington, DC
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4
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Machesky NJ, Rusnak JM, Moore EH, Dorsey CB, Ward LA. Development of a highly sensitive in vitro endothelial cell toxicity assay for evaluating ricin toxin A chain-based vaccines or therapeutics. Toxicon 2019; 167:152-161. [PMID: 31207351 DOI: 10.1016/j.toxicon.2019.06.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 06/13/2019] [Indexed: 12/20/2022]
Abstract
The ricin toxin A chain (RTA) is responsible for ricin intoxication due to inhibition of protein synthesis. RTA is also known to cause endothelial toxicity [via a 3 amino acid sequence (x)D(y) motif that acts as a natural disintegrin] resulting in vascular leak syndrome (VLS) in humans. An in vitro endothelial cell toxicity (ECT) assay was developed to evaluate if the ricin vaccine candidate (RVEc) exhibited endothelial toxicity, determined by altered transendothelial electrical resistance (TEER) across human umbilical vein endothelial cell (HUVEC) monolayers. Timepoints at 2 and 4 h were included to evaluate HUVEC monolayers before the effects of RTA ribotoxic activity are observed. Both the 3 μM and 6 μM RTA positive controls consistently demonstrated significantly reduced TEER values, compared to their corresponding vehicle control, in a time- and concentration-dependent manner at 2, 4, and 24 h. Fluorescent imaging of HUVECs exposed to 3 μM RTA showed cell rounding at 2 and 4 h and gap formation at 24 h. No changes in TEER or fluorescent imaging were observed after exposure to endothelial cell growth medium-2 (EGM-2) exchange (mock control). The negative controls, which included 2 mutant RTA vaccine derivatives [RVEc with an (x)D(y) VLS sequence modification to V76M or D75N] and bovine serum albumin (BSA), demonstrated no evidence of HUVEC toxicity at 3 μM and 6 μM concentrations. Overall, the performance of the ECT assay was consistent, allowing for the development of acceptance criteria that were related to time- and concentration-dependent decreases in TEER between 2 and 24 h.
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Affiliation(s)
- Nicholas J Machesky
- Battelle Biomedical Research Center, 1425 Plain City Georgesville Road, West Jefferson, OH, 43162, USA
| | - Janice M Rusnak
- Medical Countermeasure Systems (MCS) Joint Vaccine Acquisition Program (JVAP), 1564 Freedman Drive, Fort Detrick, MD, 21702, USA.
| | - Evan H Moore
- Battelle Biomedical Research Center, 1425 Plain City Georgesville Road, West Jefferson, OH, 43162, USA
| | - Christopher B Dorsey
- Medical Countermeasure Systems (MCS) Joint Vaccine Acquisition Program (JVAP), 1564 Freedman Drive, Fort Detrick, MD, 21702, USA
| | - Lucy A Ward
- Medical Countermeasure Systems (MCS) Joint Vaccine Acquisition Program (JVAP), 1564 Freedman Drive, Fort Detrick, MD, 21702, USA
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5
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Aitbakieva VR, Ahmad R, Singh S, Domashevskiy AV. Inhibition of ricin A-chain (RTA) catalytic activity by a viral genome-linked protein (VPg). BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:645-653. [PMID: 30822539 DOI: 10.1016/j.bbapap.2019.02.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Revised: 02/04/2019] [Accepted: 02/13/2019] [Indexed: 12/01/2022]
Abstract
Ricin is a plant derived protein toxin produced by the castor bean plant (Ricinus communis). The Centers for Disease Control (CDC) classifies ricin as a Category B biological agent. Currently, there is neither an effective vaccine that can be used to protect against ricin exposure nor a therapeutic to reverse the effects once exposed. Here we quantitatively characterize interactions between catalytic ricin A-chain (RTA) and a viral genome-linked protein (VPg) from turnip mosaic virus (TuMV). VPg and its N-terminal truncated variant, VPg1-110, bind to RTA and abolish ricin's catalytic depurination of 28S rRNA in vitro and in a cell-free rabbit reticulocyte translational system. RTA and VPg bind in a 1 to 1 stoichiometric ratio, and their binding affinity increases ten-fold as temperature elevates (5 °C to 37 °C). RTA-VPg binary complex formation is enthalpically driven and favored by entropy, resulting in an overall favorable energy, ΔG = -136.8 kJ/mol. Molecular modeling supports our experimental observations and predicts a major contribution of electrostatic interactions, suggesting an allosteric mechanism of downregulation of RTA activity through conformational changes in RTA structure, and/or disruption of binding with the ribosomal stalk. Fluorescence anisotropy studies show that heat affects the rate constant and the activation energy for the RTA-VPg complex, Ea = -62.1 kJ/mol. The thermodynamic and kinetic findings presented here are an initial lead study with promising results and provides a rational approach for synthesis of therapeutic peptides that successfully eliminate toxicity of ricin, and other cytotoxic RIPs.
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Affiliation(s)
- Valentina R Aitbakieva
- Department of Sciences, John Jay College of Criminal Justice, the City University of New York, New York 10019, NY, United States of America
| | - Rahimah Ahmad
- Department of Biology, Brooklyn College, The City University of New York, Brooklyn, New York 11210, United States of America
| | - Shaneen Singh
- Department of Biology, Brooklyn College, The City University of New York, Brooklyn, New York 11210, United States of America
| | - Artem V Domashevskiy
- Department of Sciences, John Jay College of Criminal Justice, the City University of New York, New York 10019, NY, United States of America.
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6
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Abstract
In this report, we used hydrogen exchange-mass spectrometry (HX-MS) to identify the epitopes recognized by 21 single-domain camelid antibodies (VHHs) directed against the ribosome-inactivating subunit (RTA) of ricin toxin, a biothreat agent of concern to military and public health authorities. The VHHs, which derive from 11 different B-cell lineages, were binned together based on competition ELISAs with IB2, a monoclonal antibody that defines a toxin-neutralizing hotspot ("cluster 3") located in close proximity to RTA's active site. HX-MS analysis revealed that the 21 VHHs recognized four distinct epitope subclusters (3.1-3.4). Sixteen of the 21 VHHs grouped within subcluster 3.1 and engage RTA α-helices C and G. Three VHHs grouped within subcluster 3.2, encompassing a-helices C and G, plus α-helix B. The single VHH in subcluster 3.3 engaged RTA α-helices B and G, while the epitope of the sole VHH defining subcluster 3.4 encompassed α-helices C and E, and β-strand h. Modeling these epitopes on the surface of RTA predicts that the 20 VHHs within subclusters 3.1-3.3 physically occlude RTA's active site cleft, while the single antibody in subcluster 3.4 associates on the active site's upper rim.
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7
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Protein Structure Facilitates High-Resolution Immunological Mapping. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2017; 24:CVI.00275-17. [PMID: 29046310 DOI: 10.1128/cvi.00275-17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Select agents (SA) pose unique challenges for licensing vaccines and therapies. In the case of toxin-mediated diseases, HHS assigns guidelines for SA use, oversees vaccine and therapy development, and approves animal models and approaches to identify mechanisms for toxin neutralization. In this commentary, we discuss next-generation vaccines and therapies against ricin toxin and botulinum toxin, which are regulated SA toxins that utilize structure-based approaches for countermeasures to guide rapid response to future biothreats.
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High-Definition Mapping of Four Spatially Distinct Neutralizing Epitope Clusters on RiVax, a Candidate Ricin Toxin Subunit Vaccine. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2017; 24:CVI.00237-17. [PMID: 29046307 DOI: 10.1128/cvi.00237-17] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 10/12/2017] [Indexed: 12/20/2022]
Abstract
RiVax is a promising recombinant ricin toxin A subunit (RTA) vaccine antigen that has been shown to be safe and immunogenic in humans and effective at protecting rhesus macaques against lethal-dose aerosolized toxin exposure. We previously used a panel of RTA-specific monoclonal antibodies (MAbs) to demonstrate, by competition enzyme-linked immunosorbent assay (ELISA), that RiVax elicits similar serum antibody profiles in humans and macaques. However, the MAb binding sites on RiVax have yet to be defined. In this study, we employed hydrogen exchange-mass spectrometry (HX-MS) to localize the epitopes on RiVax recognized by nine toxin-neutralizing MAbs and one nonneutralizing MAb. Based on strong protection from hydrogen exchange, the nine MAbs grouped into four spatially distinct epitope clusters (namely, clusters I to IV). Cluster I MAbs protected RiVax's α-helix B (residues 94 to 107), a protruding immunodominant secondary structure element known to be a target of potent toxin-neutralizing antibodies. Cluster II consisted of two subclusters located on the "back side" (relative to the active site pocket) of RiVax. One subcluster involved α-helix A (residues 14 to 24) and α-helices F-G (residues 184 to 207); the other encompassed β-strand d (residues 62 to 69) and parts of α-helices D-E (154 to 164) and the intervening loop. Cluster III involved α-helices C and G on the front side of RiVax, while cluster IV formed a sash from the front to back of RiVax, spanning strands b, c, and d (residues 35 to 59). Having a high-resolution B cell epitope map of RiVax will enable the development and optimization of competitive serum profiling assays to examine vaccine-induced antibody responses across species.
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Vance DJ, Tremblay JM, Rong Y, Angalakurthi SK, Volkin DB, Middaugh CR, Weis DD, Shoemaker CB, Mantis NJ. High-Resolution Epitope Positioning of a Large Collection of Neutralizing and Nonneutralizing Single-Domain Antibodies on the Enzymatic and Binding Subunits of Ricin Toxin. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2017; 24:e00236-17. [PMID: 29021300 PMCID: PMC5717184 DOI: 10.1128/cvi.00236-17] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 10/02/2017] [Indexed: 01/05/2023]
Abstract
We previously produced a heavy-chain-only antibody (Ab) VH domain (VHH)-displayed phage library from two alpacas that had been immunized with ricin toxoid and nontoxic mixtures of the enzymatic ricin toxin A subunit (RTA) and binding ricin toxin B subunit (RTB) (D. J. Vance, J. M. Tremblay, N. J. Mantis, and C. B. Shoemaker, J Biol Chem 288:36538-36547, 2013, https://doi.org/10.1074/jbc.M113.519207). Initial and subsequent screens of that library by direct enzyme-linked immunosorbent assay (ELISA) yielded more than two dozen unique RTA- and RTB-specific VHHs, including 10 whose structures were subsequently solved in complex with RTA. To generate a more complete antigenic map of ricin toxin and to define the epitopes associated with toxin-neutralizing activity, we subjected the VHH-displayed phage library to additional "pannings" on both receptor-bound ricin and antibody-captured ricin. We now report the full-length DNA sequences, binding affinities, and neutralizing activities of 68 unique VHHs: 31 against RTA, 33 against RTB, and 4 against ricin holotoxin. Epitope positioning was achieved through cross-competition ELISAs performed with a panel of monoclonal antibodies (MAbs) and verified, in some instances, with hydrogen-deuterium exchange mass spectrometry. The 68 VHHs grouped into more than 20 different competition bins. The RTA-specific VHHs with strong toxin-neutralizing activities were confined to bins that overlapped two previously identified neutralizing hot spots, termed clusters I and II. The four RTB-specific VHHs with potent toxin-neutralizing activity grouped within three adjacent bins situated at the RTA-RTB interface near cluster II. These results provide important insights into epitope interrelationships on the surface of ricin and delineate regions of vulnerability that can be exploited for the purpose of vaccine and therapeutic development.
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Affiliation(s)
- David J Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Jacqueline M Tremblay
- Department of Infectious Disease and Global Health, Tufts Cummings School of Veterinary Medicine, North Grafton, Massachusetts, USA
| | - Yinghui Rong
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Siva Krishna Angalakurthi
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, USA
| | - David B Volkin
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, USA
| | - C Russell Middaugh
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, USA
| | - David D Weis
- Department of Chemistry, University of Kansas, Lawrence, Kansas, USA
| | - Charles B Shoemaker
- Department of Infectious Disease and Global Health, Tufts Cummings School of Veterinary Medicine, North Grafton, Massachusetts, USA
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
- Department of Biomedical Sciences, University at Albany, SUNY, Albany, New York, USA
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10
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Bazzoli A, Vance DJ, Rudolph MJ, Rong Y, Angalakurthi SK, Toth RT, Middaugh CR, Volkin DB, Weis DD, Karanicolas J, Mantis NJ. Using homology modeling to interrogate binding affinity in neutralization of ricin toxin by a family of single domain antibodies. Proteins 2017; 85:1994-2008. [PMID: 28718923 DOI: 10.1002/prot.25353] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Revised: 07/13/2017] [Accepted: 07/14/2017] [Indexed: 12/12/2022]
Abstract
In this report we investigated, within a group of closely related single domain camelid antibodies (VH Hs), the relationship between binding affinity and neutralizing activity as it pertains to ricin, a fast-acting toxin and biothreat agent. The V1C7-like VH Hs (V1C7, V2B9, V2E8, and V5C1) are similar in amino acid sequence, but differ in their binding affinities and toxin-neutralizing activities. Using the X-ray crystal structure of V1C7 in complex with ricin's enzymatic subunit (RTA) as a template, Rosetta-based homology modeling coupled with energetic decomposition led us to predict that a single pairwise interaction between Arg29 on V5C1 and Glu67 on RTA was responsible for the difference in ricin toxin binding affinity between V1C7, a weak neutralizer, and V5C1, a moderate neutralizer. This prediction was borne out experimentally: substitution of Arg for Gly at position 29 enhanced V1C7's binding affinity for ricin, whereas the reverse (ie, Gly for Arg at position 29) diminished V5C1's binding affinity by >10 fold. As expected, the V5C1R29G mutant was largely devoid of toxin-neutralizing activity (TNA). However, the TNA of the V1C7G29R mutant was not correspondingly improved, indicating that in the V1C7 family binding affinity alone does not account for differences in antibody function. V1C7 and V5C1, as well as their respective point mutants, recognized indistinguishable epitopes on RTA, at least at the level of sensitivity afforded by hydrogen-deuterium mass spectrometry. The results of this study have implications for engineering therapeutic antibodies because they demonstrate that even subtle differences in epitope specificity can account for important differences in antibody function.
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Affiliation(s)
- Andrea Bazzoli
- Center for Computational Biology, University of Kansas, Lawrence, Kansas, 66045.,Computational Chemical Biology Core, University of Kansas, Lawrence, Kansas, 66047
| | - David J Vance
- New York State Department of Health, Division of Infectious Diseases, Wadsworth Center, Albany, New York, 12208
| | | | - Yinghui Rong
- New York State Department of Health, Division of Infectious Diseases, Wadsworth Center, Albany, New York, 12208
| | - Siva Krishna Angalakurthi
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, 66045
| | - Ronald T Toth
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, 66045
| | - C Russell Middaugh
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, 66045
| | - David B Volkin
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas, 66045
| | - David D Weis
- Department of Chemistry, University of Kansas, Lawrence, Kansas, 66045
| | - John Karanicolas
- Center for Computational Biology, University of Kansas, Lawrence, Kansas, 66045.,Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, 66045.,Program in Molecular Therapeutics, Fox Chase Cancer Center, Philadelphia, Pennsylvania, 19111
| | - Nicholas J Mantis
- New York State Department of Health, Division of Infectious Diseases, Wadsworth Center, Albany, New York, 12208
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11
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Sarkes DA, Hurley MM, Stratis-Cullum DN. Unraveling the Roots of Selectivity of Peptide Affinity Reagents for Structurally Similar Ribosomal Inactivating Protein Derivatives. Molecules 2016; 21:E1504. [PMID: 27834872 PMCID: PMC6272918 DOI: 10.3390/molecules21111504] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 11/02/2016] [Accepted: 11/04/2016] [Indexed: 11/17/2022] Open
Abstract
Peptide capture agents have become increasingly useful tools for a variety of sensing applications due to their ease of discovery, stability, and robustness. Despite the ability to rapidly discover candidates through biopanning bacterial display libraries and easily mature them to Protein Catalyzed Capture (PCC) agents with even higher affinity and selectivity, an ongoing challenge and critical selection criteria is that the peptide candidates and final reagent be selective enough to replace antibodies, the gold-standard across immunoassay platforms. Here, we have discovered peptide affinity reagents against abrax, a derivative of abrin with reduced toxicity. Using on-cell Fluorescence Activated Cell Sorting (FACS) assays, we show that the peptides are highly selective for abrax over RiVax, a similar derivative of ricin originally designed as a vaccine, with significant structural homology to abrax. We rank the newly discovered peptides for strongest affinity and analyze three observed consensus sequences with varying affinity and specificity. The strongest (Tier 1) consensus was FWDTWF, which is highly aromatic and hydrophobic. To better understand the observed selectivity, we use the XPairIt peptide-protein docking protocol to analyze binding location predictions of the individual Tier 1 peptides and consensus on abrax and RiVax. The binding location profiles on the two proteins are quite distinct, which we determine is due to differences in pocket size, pocket environment (including hydrophobicity and electronegativity), and steric hindrance. This study provides a model system to show that peptide capture candidates can be quite selective for a structurally similar protein system, even without further maturation, and offers an in silico method of analysis for understanding binding and down-selecting candidates.
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Affiliation(s)
- Deborah A Sarkes
- Biotechnology Branch, Sensors and Electron Devices Directorate, US Army Research Laboratory, Adelphi, MD 20783, USA.
| | - Margaret M Hurley
- Biotechnology Branch, Sensors and Electron Devices Directorate, US Army Research Laboratory, Adelphi, MD 20783, USA.
| | - Dimitra N Stratis-Cullum
- Biotechnology Branch, Sensors and Electron Devices Directorate, US Army Research Laboratory, Adelphi, MD 20783, USA.
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12
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Legler PM, Compton JR, Hale ML, Anderson GP, Olson MA, Millard CB, Goldman ER. Stability of isolated antibody-antigen complexes as a predictive tool for selecting toxin neutralizing antibodies. MAbs 2016; 9:43-57. [PMID: 27660893 PMCID: PMC5240650 DOI: 10.1080/19420862.2016.1236882] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ricin is an A-B ribosome inactivating protein (RIP) toxin composed of an A-chain subunit (RTA) that contains a catalytic N-glycosidase and a B-chain (RTB) lectin domain that binds cell surface glycans. Ricin exploits retrograde transport to enter into the Golgi and the endoplasmic reticulum, and then dislocates into the cytoplasm where it can reach its substrate, the rRNA. A subset of isolated antibodies (Abs) raised against the RTA subunit protect against ricin intoxication, and RTA-based vaccine immunogens have been shown to provide long-lasting protective immunity against the holotoxin. Anti-RTA Abs are unlikely to cross a membrane and reach the cytoplasm to inhibit the enzymatic activity of the A-chain. Moreover, there is not a strict correlation between the apparent binding affinity (Ka) of anti-RTA Abs and their ability to successfully neutralize ricin toxicity. Some anti-RTA antibodies are toxin-neutralizing, whereas others are not. We hypothesize that neutralizing anti-RTA Abs may interfere selectively with conformational change(s) or partial unfolding required for toxin internalization. To test this hypothesis, we measured the melting temperatures (Tm) of neutralizing single-domain Ab (sdAb)-antigen (Ag) complexes relative to the Tm of the free antigen (Tm-shift = Tmcomplex – TmAg), and observed increases in the Tmcomplex of 9–20 degrees. In contrast, non-neutralizing sdAb-Ag complexes shifted the TmComplex by only 6–7 degrees. A strong linear correlation (r2 = 0.992) was observed between the magnitude of the Tm-shift and the viability of living cells treated with the sdAb and ricin holotoxin. The Tm-shift of the sdAb-Ag complex provided a quantitative biophysical parameter that could be used to predict and rank-order the toxin-neutralizing activities of Abs. We determined the first structure of an sdAb-RTA1-33/44-198 complex, and examined other sdAb-RTA complexes. We found that neutralizing sdAb bound to regions involved in the early stages of unfolding. These Abs likely interfere with steps preceding or following endocytosis that require conformational changes. This method may have utility for the characterization or rapid screening of other Ab that act to prevent conformational changes or unfolding as part of their mechanism of action.
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Affiliation(s)
| | | | - Martha L Hale
- c US Army Medical Research Institute of Infectious Diseases , Frederick , MD , USA
| | | | - Mark A Olson
- c US Army Medical Research Institute of Infectious Diseases , Frederick , MD , USA
| | - Charles B Millard
- c US Army Medical Research Institute of Infectious Diseases , Frederick , MD , USA
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13
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Vance DJ, Mantis NJ. Progress and challenges associated with the development of ricin toxin subunit vaccines. Expert Rev Vaccines 2016; 15:1213-22. [PMID: 26998662 PMCID: PMC5193006 DOI: 10.1586/14760584.2016.1168701] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The past several years have seen major advances in the development of a safe and efficacious ricin toxin vaccine, including the completion of two Phase I clinical trials with two different recombinant A subunit (RTA)-based vaccines: RiVax™ and RVEc™ adsorbed to aluminum salt adjuvant, as well as a non-human primate study demonstrating that parenteral immunization with RiVax elicits a serum antibody response that was sufficient to protect against a lethal dose aerosolized ricin exposure. One of the major obstacles moving forward is assessing vaccine efficacy in humans, when neither ricin-specific serum IgG endpoint titers nor toxin-neutralizing antibody levels are accepted as definitive predictors of protective immunity. In this review we summarize ongoing efforts to leverage recent advances in our understanding of RTA-antibody interactions at the structural level to develop novel assays to predict vaccine efficacy in humans.
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Affiliation(s)
- David J. Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Nicholas J. Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA
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14
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Wahome N, Sully E, Singer C, Thomas JC, Hu L, Joshi SB, Volkin DB, Fang J, Karanicolas J, Jacobs DJ, Mantis NJ, Middaugh CR. Novel Ricin Subunit Antigens With Enhanced Capacity to Elicit Toxin-Neutralizing Antibody Responses in Mice. J Pharm Sci 2016; 105:1603-1613. [PMID: 26987947 PMCID: PMC4846473 DOI: 10.1016/j.xphs.2016.02.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 01/26/2016] [Accepted: 02/09/2016] [Indexed: 02/07/2023]
Abstract
RiVax is a candidate ricin toxin subunit vaccine antigen that has proven to be safe in human phase I clinical trials. In this study, we introduced double and triple cavity-filling point mutations into the RiVax antigen with the expectation that stability-enhancing modifications would have a beneficial effect on overall immunogenicity of the recombinant proteins. We demonstrate that 2 RiVax triple mutant derivatives, RB (V81L/C171L/V204I) and RC (V81I/C171L/V204I), when adsorbed to aluminum salts adjuvant and tested in a mouse prime-boost-boost regimen were 5- to 10-fold more effective than RiVax at eliciting toxin-neutralizing serum IgG antibody titers. Increased toxin neutralizing antibody values and seroconversion rates were evident at different antigen dosages and within 7 days after the first booster. Quantitative stability/flexibility relationships analysis revealed that the RB and RC mutations affect rigidification of regions spanning residues 98-103, which constitutes a known immunodominant neutralizing B-cell epitope. A more detailed understanding of the immunogenic nature of RB and RC may provide insight into the fundamental relationship between local protein stability and antibody reactivity.
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Affiliation(s)
- Newton Wahome
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Erin Sully
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York 12208
| | - Christopher Singer
- Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, North Carolina 28223
| | - Justin C Thomas
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Lei Hu
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Sangeeta B Joshi
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - David B Volkin
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Jianwen Fang
- Applied Bioinformatics Laboratory, Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66047
| | - John Karanicolas
- Department of Molecular Biosciences, Center for Computational Biology, University of Kansas, Lawrence, Kansas 66045
| | - Donald J Jacobs
- Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, North Carolina 28223.
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York 12208; Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, New York 12201.
| | - C Russell Middaugh
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047.
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15
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Wang J, Gao S, Xin W, Kang L, Xu N, Zhang T, Liu W, Wang J. A novel recombinant vaccine protecting mice against abrin intoxication. Hum Vaccin Immunother 2016; 11:1361-7. [PMID: 26086588 PMCID: PMC4514378 DOI: 10.1080/21645515.2015.1008879] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Abrin toxin (AT) consisting of an A chain and a B chain is a potential agent for bioterrorism and an effective vaccine against AT poisoning is urgently required. In this study, AT B chain (ATB) was successfully expressed in the Escherichia coli (E. coli) and assessed the protection capacity against AT intoxication. The recombinant ATB (rATB) subunit induces a good immune response after 4 immunizations. All BALB/c mice immunized intraperitoneally (i.p.) with the purified rATB protein survived after challenged with 5 × LD50 of AT. Transfusion of sera from immunized mice provided passive protection in naive mice. Furthermore, histological findings showed that immunization with rATB decreased the severity of toxin-related tissue damage. This work indicates that the rATB protein may be a promising vaccine candidate against human exposure to AT.
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Key Words
- AT, abrin toxin
- ATB, abrin toxin B chain
- B chain
- E. coli, Escherichia coli
- ELISA, enzyme-linked immunosorbent assay
- LD50, 50% lethal dose
- PBS, phosphate-buffered saline solution
- RT, ricin toxin
- RTB, ricin toxin B chain
- SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis
- abrin toxin
- bioterrorism
- i.p, intraperitoneal or intraperitoneally
- immunogen
- pAb, polyclonal antibody
- vaccine candidate
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Affiliation(s)
- Junhong Wang
- a State Key Laboratory of Pathogen and Biosecurity; Beijing Institute of Microbiology and Epidemiology ; Beijing , PR China
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16
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Brey RN, Mantis NJ, Pincus SH, Vitetta ES, Smith LA, Roy CJ. Recent advances in the development of vaccines against ricin. Hum Vaccin Immunother 2016; 12:1196-201. [PMID: 26810367 DOI: 10.1080/21645515.2015.1124202] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Several promising subunit vaccines against ricin toxin (RT) have been developed during the last decade and are now being tested for safety and immunogenicity in humans and for efficacy in nonhuman primates. The incentive to develop a preventive vaccine as a countermeasure against RT use as a bioweapon is based on the high toxicity of RT after aerosol exposure, its environmental stability, abundance, and ease of purification. RT is the second most lethal biological toxin and is considered a "universal toxin" because it can kill all eukaryotic cells through binding to ubiquitous cell surface galactosyl residues. RT has two subunits conjoined by a single disulfide linkage: RTB, which binds galactosyl residues and RTA which enzymatically inactivates ribosomes intracellularly by cleavage ribosomal RNA. Attenuation of toxicity by elimination of the active site or introduction of other structural mutations of RTA has generated two similar clinical subunit vaccine candidates which induce antibodies in both humans and nonhuman primates. In rhesus macaques, inhaled RT causes rapid lung necrosis and fibrosis followed by death. After parenteral vaccination with RTA vaccine, macaques can be protected against aerosol RT exposure, suggesting that circulating antibodies can protect lung mucosa. Vaccination induces RT-neutralizing antibodies, the most likely correlate of protection. Macaques responded to conformational determinants in an RTA vaccine formulation, indicating preservation of RTA structure during initial manufacture. Comparative mapping studies have also demonstrated that macaques and humans recognize the same epitopes, significant in the study of macaques as a model during development of vaccines which cannot be tested for efficacy in humans.
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Affiliation(s)
| | - Nicholas J Mantis
- b Division of Infectious Disease , Wadsworth Center, New York State Department of Health, Albany, NY, USA Department of Biomedical Sciences, University of Albany School of Public Health , Albany , NY , USA
| | - Seth H Pincus
- c Departments of Pediatrics and Microbiology , Louisiana State University School of Medicine, Children's Hospital , New Orleans , LA , USA
| | - Ellen S Vitetta
- d Departments of Immunology and Microbiology , The University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Leonard A Smith
- e Medical Countermeasures Technology, US Army Medical Research Institute of Infectious Diseases , Fort Detrick , MD , USA
| | - Chad J Roy
- f Division of Microbiology, Tulane National Primate Research Center , Covington , LA , USA.,g Department of Microbiology and Immunology , Tulane School of Medicine , New Orleans , LA , USA
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17
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Thermostable ricin vaccine protects rhesus macaques against aerosolized ricin: Epitope-specific neutralizing antibodies correlate with protection. Proc Natl Acad Sci U S A 2015; 112:3782-7. [PMID: 25775591 DOI: 10.1073/pnas.1502585112] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Ricin toxin (RT) is the second most lethal toxin known; it has been designated by the CDC as a select agent. RT is made by the castor bean plant; an estimated 50,000 tons of RT are produced annually as a by-product of castor oil. RT has two subunits, a ribotoxic A chain (RTA) and galactose-binding B chain (RTB). RT binds to all mammalian cells and once internalized, a single RTA catalytically inactivates all of the ribosomes in a cell. Administered as an aerosol, RT causes rapid lung damage and fibrosis followed by death. There are no Food and Drug Administration-approved vaccines and treatments are only effective in the first few hours after exposure. We have developed a recombinant RTA vaccine that has two mutations V76M/Y80A (RiVax). The protein is expressed in Escherichia coli and is nontoxic and immunogenic in mice, rabbits, and humans. When vaccinated mice are challenged with injected, aerosolized, or orally administered (gavaged) RT, they are completely protected. We have now developed a thermostable, aluminum-adjuvant-containing formulation of RiVax and tested it in rhesus macaques. After three injections, the animals developed antibodies that completely protected them from a lethal dose of aerosolized RT. These antibodies neutralized RT and competed to varying degrees with a panel of neutralizing and nonneutralizing mouse monoclonal antibodies known to recognize specific epitopes on native RTA. The resulting antibody competition profile could represent an immunologic signature of protection. Importantly, the same signature was observed using sera from RiVax-immunized humans.
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18
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Rudolph MJ, Vance DJ, Cheung J, Franklin MC, Burshteyn F, Cassidy MS, Gary EN, Herrera C, Shoemaker CB, Mantis NJ. Crystal structures of ricin toxin's enzymatic subunit (RTA) in complex with neutralizing and non-neutralizing single-chain antibodies. J Mol Biol 2014; 426:3057-68. [PMID: 24907552 PMCID: PMC4128236 DOI: 10.1016/j.jmb.2014.05.026] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Revised: 05/17/2014] [Accepted: 05/25/2014] [Indexed: 10/25/2022]
Abstract
Ricin is a select agent toxin and a member of the RNA N-glycosidase family of medically important plant and bacterial ribosome-inactivating proteins. In this study, we determined X-ray crystal structures of the enzymatic subunit of ricin (RTA) in complex with the antigen binding domains (VHH) of five unique single-chain monoclonal antibodies that differ in their respective toxin-neutralizing activities. None of the VHHs made direct contact with residues involved in RTA's RNA N-glycosidase activity or induced notable allosteric changes in the toxin's subunit. Rather, the five VHHs had overlapping structural epitopes on the surface of the toxin and differed in the degree to which they made contact with prominent structural elements in two folding domains of the RTA. In general, RTA interactions were influenced most by the VHH CDR3 (CDR, complementarity-determining region) elements, with the most potent neutralizing antibody having the shortest and most conformationally constrained CDR3. These structures provide unique insights into the mechanisms underlying toxin neutralization and provide critically important information required for the rational design of ricin toxin subunit vaccines.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
| | - Jonah Cheung
- New York Structural Biology Center, New York, NY 10027, USA
| | | | | | | | - Ebony N Gary
- New York Structural Biology Center, New York, NY 10027, USA
| | - Cristina Herrera
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, USA
| | | | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, USA.
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19
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Ramage JG, Prentice KW, Morse SA, Carter AJ, Datta S, Drumgoole R, Gargis SR, Griffin-Thomas L, Hastings R, Masri HP, Reed MS, Sharma SK, Singh AK, Swaney E, Swanson T, Gauthier C, Toney D, Pohl J, Shakamuri P, Stuchlik O, Elder IA, Estacio PL, Garber EAE, Hojvat S, Kellogg RB, Kovacs G, Stanker L, Weigel L, Hodge DR, Pillai SP. Comprehensive Laboratory Evaluation of a Specific Lateral Flow Assay for the Presumptive Identification of Abrin in Suspicious White Powders and Environmental Samples. Biosecur Bioterror 2014; 12:49-62. [DOI: 10.1089/bsp.2013.0080] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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20
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Comparative efficacy of two leading candidate ricin toxin a subunit vaccines in mice. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2013; 20:789-94. [PMID: 23515013 DOI: 10.1128/cvi.00098-13] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The two leading ricin toxin vaccine candidates, RVEc and RiVax, are recombinant derivatives of the toxin's 267-amino-acid enzymatic A chain (RTA). RVEc is truncated at the C terminus (residues 199 to 267) to improve protein thermostability, while RiVax has two point mutations (V76M and Y80A) that eliminate the RNA N-glycosidase activity of RTA, as well as its ability to induce vascular leak syndrome. The two vaccines have never been directly compared in terms of their ability to stimulate RTA-specific antibodies (Abs), toxin-neutralizing activity (TNA), or protective immunity. To address this issue, groups of female BALB/c mice were immunized two or three times with Alhydrogel-adsorbed RiVax or RVEc at a range of doses (0.3 to 20 μg) and then challenged with 10 50% lethal doses (LD(50)s) of ricin. We found that the vaccines were equally effective at eliciting protective immunity at the doses tested. There were, however, quantitative differences in the antibody responses. RVEc tended to elicit higher levels of ricin-specific RTA IgG and TNA than did RiVax. Pepscan analysis revealed that serum Abs elicited by RVEc were skewed toward a solvent-exposed immunodominant α-helix known to be the target of potent toxin-neutralizing Abs. Finally, immunodepletion experiments suggest that the majority of toxin-neutralizing Abs elicited by RiVax were confined to residues 1 to 198, possibly explaining the equal effectiveness of RVEc as a vaccine.
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21
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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: 6] [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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22
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Pilot phase IB clinical trial of an alhydrogel-adsorbed recombinant ricin vaccine. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2012; 19:1697-9. [PMID: 22914366 DOI: 10.1128/cvi.00381-12] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
There is no FDA-approved vaccine for the potent plant toxin ricin. We have developed a recombinant ricin vaccine, RiVax. Without adjuvant it is safe and immunogenic in mice, rabbits, and humans. Based on our studies in mice, we now report the results of a small clinical trial with Alhydrogel-adsorbed RiVax.
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