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Roy CJ, Ehrbar D, Van Slyke G, Doering J, Didier PJ, Doyle-Meyers L, Donini O, Vitetta ES, Mantis NJ. Serum antibody profiling identifies vaccine-induced correlates of protection against aerosolized ricin toxin in rhesus macaques. NPJ Vaccines 2022; 7:164. [PMID: 36526642 PMCID: PMC9755799 DOI: 10.1038/s41541-022-00582-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 11/24/2022] [Indexed: 12/23/2022] Open
Abstract
Inhalation of the biothreat agent, ricin toxin (RT), provokes a localized inflammatory response associated with pulmonary congestion, edema, neutrophil infiltration, and severe acute respiratory distress. The extreme toxicity of RT is the result of the toxin's B chain (RTB) promoting rapid uptake into alveolar macrophages and lung epithelial cells, coupled with the A chain's (RTA) potent ribosome-inactivating properties. We previously reported that intramuscular vaccination of rhesus macaques with a lyophilized, alum-adsorbed recombinant RTA subunit vaccine (RiVax®) was sufficient to confer protection against a lethal dose of aerosolized RT. That study implicated RT-specific serum IgG, toxin-neutralizing activity (TNA), and epitope-specific responses as being associated with immunity. However, it was not possible to define actual correlates of protection (COP) because all vaccinated animals survived the RT challenge. We addressed the issue of COP in the current study, by vaccinating groups of rhesus macaques with RiVax® following the previously determined protective regimen (100 µg on study days 0, 30 and 60) or one of two anticipated suboptimal regimens (100 µg on study days 30 and 60; 35 µg on study days 0, 30, and 60). Two unvaccinated animals served as controls. The animals were challenged with ~5 × LD50s of aerosolized RT on study day 110. We report that all vaccinated animals seroconverted prior to RT challenge, with the majority also having measurable TNA, although neither antibody levels nor TNA reached statistical significance with regard to a correlation with protection. By contrast, survival correlated with pre-challenge, epitope-specific serum IgG levels, derived from a competitive sandwich ELISA using a panel of toxin-neutralizing monoclonal antibodies directed against distinct epitopes on RiVax®. The identification of a species-neutral, competitive ELISA that correlates with vaccine-induced protection against RT in nonhuman represents an important advance in the development of medical countermeasures (MCM) against a persistent biothreat.
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Affiliation(s)
- Chad J Roy
- Tulane National Primate Research Center, Covington, LA, 70433, USA.
| | - Dylan Ehrbar
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, 12208, USA
| | - Greta Van Slyke
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, 12208, USA
| | - Jennifer Doering
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, 12208, USA
| | - Peter J Didier
- Tulane National Primate Research Center, Covington, LA, 70433, USA
| | | | | | - Ellen S Vitetta
- Departments of Immunology and Microbiology, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA.
| | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, 12208, USA.
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2
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Deng M, Su D, Xiao N, Zhang Z, Wang Y, Zong F, Li S, Wang J, Zhou D, Zhao Y, Yang H. Gdf15 deletion exacerbates acute lung injuries induced by intratracheal inoculation of aerosolized ricin in mice. Toxicology 2022; 469:153135. [DOI: 10.1016/j.tox.2022.153135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 02/16/2022] [Accepted: 02/17/2022] [Indexed: 10/19/2022]
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3
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Novak H, Doering J, Ehrbar D, Donini O, Mantis NJ. Durable Immunity to Ricin Toxin Elicited by a Thermostable, Lyophilized Subunit Vaccine. mSphere 2021; 6:e0075021. [PMID: 34730377 PMCID: PMC8565519 DOI: 10.1128/msphere.00750-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/15/2021] [Indexed: 11/26/2022] Open
Abstract
The development of vaccines against biothreat toxins like ricin (RT) is considered an integral component of the U.S. national security efforts. RiVax is a thermostable, lyophilized RT subunit vaccine adsorbed to aluminum salt adjuvant intended for use by military personnel and first responders. Phase 1 studies indicated that RiVax is safe and immunogenic, while a three-dose intramuscular vaccination regimen in nonhuman primates elicited protection against lethal dose RT challenge by aerosol. Here, we investigated, in a mouse model, the durability of RiVax-induced antibody responses and corresponding immunity to lethal dose RT challenge. Groups of mice were subcutaneously administered 3 or 1 μg of RiVax on days 0 and 21 and challenged with 10× 50% lethal dose (LD50) RT by injection at six different intervals over the course of 12 months. Serum antibody titers and epitope-specific competition assays were determined prior to each challenge. We report that the two-dose, 3-μg regimen conferred near-complete protection against RT challenge on day 35 and complete protection thereafter (challenge days 65, 95, 125, 245, and 365). The two-dose, 3-μg regimen was superior to the 1-μg regimen as revealed by slight differences in survival and morbidity scores (e.g., hypoglycemia, weight loss) on challenge days 35 and 365. In separate experiments, a single 3-μg RiVax vaccination proved only marginally effective at eliciting protective immunity to RT, underscoring the necessity of a prime-boost regimen to achieve full and long-lasting protection against RT. IMPORTANCE Ricin toxin (RT) is a notorious biothreat, as exposure to even trace amounts via injection or inhalation can induce organ failure and death within a matter of hours. In this study, we advance the preclinical testing of a candidate RT vaccine known as RiVax. RiVax is a recombinant nontoxic derivative of RT's enzymatic subunit that has been evaluated for safety in phase I clinical trials and efficacy in a variety of animal models. We demonstrate that two doses of RiVax are sufficient to protect mice from lethal dose RT challenge for up to 1 year. We describe kinetics and other immune parameters of the antibody response to RiVax and discuss how these immune factors may translate to humans.
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Affiliation(s)
- Hayley Novak
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA
| | - Jennifer Doering
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Dylan Ehrbar
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | | | - Nicholas J. Mantis
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
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4
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Rudolph MJ, Poon AY, Kavaliauskiene S, Myrann AG, Reynolds-Peterson C, Davis SA, Sandvig K, Vance DJ, Mantis NJ. Structural Analysis of Toxin-Neutralizing, Single-Domain Antibodies that Bridge Ricin's A-B Subunit Interface. J Mol Biol 2021; 433:167086. [PMID: 34089718 DOI: 10.1016/j.jmb.2021.167086] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Revised: 05/18/2021] [Accepted: 05/27/2021] [Indexed: 01/20/2023]
Abstract
Ricin toxin kills mammalian cells with notorious efficiency. The toxin's B subunit (RTB) is a Gal/GalNAc-specific lectin that attaches to cell surfaces and promotes retrograde transport of ricin's A subunit (RTA) to the trans Golgi network (TGN) and endoplasmic reticulum (ER). RTA is liberated from RTB in the ER and translocated into the cell cytoplasm, where it functions as a ribosome-inactivating protein. While antibodies against ricin's individual subunits have been reported, we now describe seven alpaca-derived, single-domain antibodies (VHHs) that span the RTA-RTB interface, including four Tier 1 VHHs with IC50 values <1 nM. Crystal structures of each VHH bound to native ricin holotoxin revealed three different binding modes, based on contact with RTA's F-G loop (mode 1), RTB's subdomain 2γ (mode 2) or both (mode 3). VHHs in modes 2 and 3 were highly effective at blocking ricin attachment to HeLa cells and immobilized asialofetuin, due to framework residues (FR3) that occupied the 2γ Gal/GalNAc-binding pocket and mimic ligand. The four Tier 1 VHHs also interfered with intracellular functions of RTB, as they neutralized ricin in a post-attachment cytotoxicity assay (e.g., the toxin was bound to cell surfaces before antibody addition) and reduced the efficiency of toxin transport to the TGN. We conclude that the RTA-RTB interface is a target of potent toxin-neutralizing antibodies that interfere with both extracellular and intracellular events in ricin's cytotoxic pathway.
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Affiliation(s)
| | - Amanda Y Poon
- Department of Biomedical Sciences, University at Albany, Albany, NY, USA; Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Simona Kavaliauskiene
- Department of Molecular Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Montebello, Oslo, Norway
| | - Anne Grethe Myrann
- Department of Molecular Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Montebello, Oslo, Norway
| | - Claire Reynolds-Peterson
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Simon A Davis
- New York Structural Biology Center, New York, NY, USA
| | - Kirsten Sandvig
- Department of Molecular Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Montebello, Oslo, Norway; Department of Biosciences, University of Oslo, Oslo, Norway
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA.
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5
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Oliveira G, Schneedorf JM. An Electrochemical Approach to Follow and Evaluate the Kinetic Catalysis of Ricin on hsDNA. Life (Basel) 2021; 11:life11050405. [PMID: 33946642 PMCID: PMC8145570 DOI: 10.3390/life11050405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 04/15/2021] [Accepted: 04/19/2021] [Indexed: 11/16/2022] Open
Abstract
International authorities classify the ricin toxin, present in castor seeds, as a potential agent for use in bioterrorism. Therefore, the detection, identification, and characterization of ricin are considered the first actions for its risk assessment during a suspected exposure, parallel to the development of therapeutic and medical countermeasures. In this study, we report the kinetic analysis of electro-oxidation of adenine released from hsDNA by the catalytic action of ricin by square wave voltammetry. The results suggest that ricin-mediated adenine release exhibited an unusual kinetic profile, with a progress curve controlled by the accumulation of the product and the values of the kinetic constants of 46.6 µM for Km and 2000 min−1 for kcat, leading to a catalytic efficiency of 7.1 × 105 s−1 M−1.
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A Simple, Fast and Portable Method for Electrochemical Detection of Adenine Released by Ricin Enzymatic Activity. Toxins (Basel) 2021; 13:toxins13040238. [PMID: 33810228 PMCID: PMC8066795 DOI: 10.3390/toxins13040238] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 03/19/2021] [Accepted: 03/22/2021] [Indexed: 12/20/2022] Open
Abstract
International authorities classify ricin toxin present in castor seed as a potential agent for use in bioterrorism. Therefore, the detection, identification, and characterization of ricin in various sample matrices are considered necessary actions for risk assessment during a suspected exposure. This study reports a portable electrochemical assay for detecting active ricin based on the adenine electro-oxidation released from herring sperm DNA substrate by its catalytic action. Also, kinetic parameters were calculated, and the values were Km of 3.14 µM and Kcat 2107 min−1. A linear response was found in optimized experimental conditions for ricin concentrations ranging from 8 to 120 ng/mL, and with a detection limit of 5.14 ng/mL. This proposed detection strategy emphasizes the possibility of field detection of active ricin in food matrices and can be applied to other endonucleolytic activities.
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7
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Slyke GV, Ehrbar DJ, Doering J, Yates JL, Vitetta ES, Donini O, Mantis NJ. Endpoint and epitope-specific antibody responses as correlates of vaccine-mediated protection of mice against ricin toxin. Vaccine 2020; 38:6721-6729. [PMID: 32891474 DOI: 10.1016/j.vaccine.2020.08.047] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 08/11/2020] [Accepted: 08/18/2020] [Indexed: 12/17/2022]
Abstract
The successful licensure of vaccines for biodefense is contingent upon the availability of well-established correlates of protection (CoP) in at least two animal species that can be applied to humans, without the need to assess efficacy in the clinic. In this report we describe a multivariate model that combines pre-challenge serum antibody endpoint titers (EPT) and values derived from an epitope profiling immune-competition capture (EPICC) assay as a predictor in mice of vaccine-mediated immunity against ricin toxin (RT), a Category B biothreat. EPICC is a modified competition ELISA in which serum samples from vaccinated mice were assessed for their ability to inhibit the capture of soluble, biotinylated (b)-RT by a panel of immobilized monoclonal antibodies (mAbs) directed against four immunodominant toxin-neutralizing regions on the enzymatic A chain (RTA) of RT. In a test cohort of mice (n = 40) vaccinated with suboptimal doses of the RTA subunit vaccine, RiVax®, we identified two mAbs, PB10 and SyH7, which had EPICC inhibition values in pre-challenge serum samples that correlated with survival following a challenge with 5 × LD50 of RT administered by intraperitoneal (IP) injection. Analysis of a larger cohort of mice (n = 645) revealed that a multivariate model combining endpoint titers and EPICC values for PB10 and SyH7 as predictive variables had significantly higher statistical power than any one of the independent variables alone. Establishing the correlates of vaccine-mediated protection in mice represents an important steppingstone in the development of RiVax® as a medical countermeasure under the United States Food and Drug Administration's "Animal Rule."
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Affiliation(s)
- Greta Van Slyke
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Dylan J Ehrbar
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Jennifer Doering
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Jennifer L Yates
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Ellen S Vitetta
- Department of Immunology and Microbiology, University of Texas Southwestern Medical School, Dallas, TX, United States
| | | | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States.
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8
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Rong Y, Torres-Velez FJ, Ehrbar D, Doering J, Song R, Mantis NJ. An intranasally administered monoclonal antibody cocktail abrogates ricin toxin-induced pulmonary tissue damage and inflammation. Hum Vaccin Immunother 2019; 16:793-807. [PMID: 31589555 DOI: 10.1080/21645515.2019.1664243] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Ricin toxin, a plant-derived, mannosylated glycoprotein, elicits an incapacitating and potentially lethal inflammatory response in the airways following inhalation. Uptake of ricin by alveolar macrophages (AM) and other pulmonary cell types occurs via two parallel pathways: one mediated by ricin's B subunit (RTB), a galactose-specific lectin, and one mediated by the mannose receptor (MR;CD206). Ricin's A subunit (RTA) is a ribosome-inactivating protein that triggers apoptosis in mammalian cells. It was recently reported that a single monoclonal antibody (MAb), PB10, directed against an immunodominant epitope on RTA and administered intravenously, was able to rescue Rhesus macaques from lethal aerosol dose of ricin. In this study, we now demonstrate in mice that the effectiveness PB10 is significantly improved when combined with a second MAb, SylH3, against RTB. Mice treated with PB10 alone survived lethal-dose intranasal ricin challenge, but experienced significant weight loss, moderate pulmonary inflammation (e.g., elevated IL-1 and IL-6 levels, PMN influx), and apoptosis of lung macrophages. In contrast, mice treated with the PB10/SylH3 cocktail were essentially impervious to pulmonary ricin toxin exposure, as evidenced by no weight loss, no change in local IL-1 and IL-6 levels, retention of lung macrophages, and a significant dampening of PMN recruitment into the bronchoalveolar lavage (BAL) fluids. The PB10/SylH3 cocktail only marginally reduced ricin binding to target cells in the BAL, suggesting that the antibody mixture neutralizes ricin by interfering with one or more steps in the RTB- and MR-dependent uptake pathways.
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Affiliation(s)
- Yinghui Rong
- New York State Department of Health, Division of Infectious Disease, Wadsworth Center, Albany, NY, USA
| | - Fernando J Torres-Velez
- New York State Department of Health, Division of Infectious Disease, Wadsworth Center, Albany, NY, USA
| | - Dylan Ehrbar
- New York State Department of Health, Division of Infectious Disease, Wadsworth Center, Albany, NY, USA
| | - Jennifer Doering
- New York State Department of Health, Division of Infectious Disease, Wadsworth Center, Albany, NY, USA
| | - Renjie Song
- New York State Department of Health, Division of Infectious Disease, Wadsworth Center, Albany, NY, USA
| | - Nicholas J Mantis
- New York State Department of Health, Division of Infectious Disease, Wadsworth Center, Albany, NY, USA
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Intracellular Transport and Cytotoxicity of the Protein Toxin Ricin. Toxins (Basel) 2019; 11:toxins11060350. [PMID: 31216687 PMCID: PMC6628406 DOI: 10.3390/toxins11060350] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 06/13/2019] [Accepted: 06/14/2019] [Indexed: 12/17/2022] Open
Abstract
Ricin can be isolated from the seeds of the castor bean plant (Ricinus communis). It belongs to the ribosome-inactivating protein (RIP) family of toxins classified as a bio-threat agent due to its high toxicity, stability and availability. Ricin is a typical A-B toxin consisting of a single enzymatic A subunit (RTA) and a binding B subunit (RTB) joined by a single disulfide bond. RTA possesses an RNA N-glycosidase activity; it cleaves ribosomal RNA leading to the inhibition of protein synthesis. However, the mechanism of ricin-mediated cell death is quite complex, as a growing number of studies demonstrate that the inhibition of protein synthesis is not always correlated with long term ricin toxicity. To exert its cytotoxic effect, ricin A-chain has to be transported to the cytosol of the host cell. This translocation is preceded by endocytic uptake of the toxin and retrograde traffic through the trans-Golgi network (TGN) and the endoplasmic reticulum (ER). In this article, we describe intracellular trafficking of ricin with particular emphasis on host cell factors that facilitate this transport and contribute to ricin cytotoxicity in mammalian and yeast cells. The current understanding of the mechanisms of ricin-mediated cell death is discussed as well. We also comment on recent reports presenting medical applications for ricin and progress associated with the development of vaccines against this toxin.
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10
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Roy CJ, Ehrbar DJ, Bohorova N, Bohorov O, Kim D, Pauly M, Whaley K, Rong Y, Torres-Velez FJ, Vitetta ES, Didier PJ, Doyle-Meyers L, Zeitlin L, Mantis NJ. Rescue of rhesus macaques from the lethality of aerosolized ricin toxin. JCI Insight 2019; 4:124771. [PMID: 30626745 DOI: 10.1172/jci.insight.124771] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2018] [Accepted: 11/27/2018] [Indexed: 12/12/2022] Open
Abstract
Ricin toxin (RT) ranks at the top of the list of bioweapons of concern to civilian and military personnel alike, due to its high potential for morbidity and mortality after inhalation. In nonhuman primates, aerosolized ricin triggers severe acute respiratory distress characterized by perivascular and alveolar edema, neutrophilic infiltration, and severe necrotizing bronchiolitis and alveolitis. There are currently no approved countermeasures for ricin intoxication. Here, we report the therapeutic potential of a humanized mAb against an immunodominant epitope on ricin's enzymatic A chain (RTA). Rhesus macaques that received i.v. huPB10 4 hours after a lethal dose of ricin aerosol exposure survived toxin challenge, whereas control animals succumbed to ricin intoxication within 30 hours. Antibody intervention at 12 hours resulted in the survival of 1 of 5 monkeys. Changes in proinflammatory cytokine, chemokine, and growth factor profiles in bronchial alveolar lavage fluids before and after toxin challenge successfully clustered animals by treatment group and survival, indicating a relationship between local tissue damage and experimental outcome. This study represents the first demonstration, to our knowledge, in nonhuman primates that the lethal effects of inhalational ricin exposure can be negated by a drug candidate, and it opens up a path forward for product development.
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Affiliation(s)
- Chad J Roy
- Tulane National Primate Research Center (TNPRC), Covington, Louisiana, USA
| | - Dylan J Ehrbar
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | | | | | - Do Kim
- Mapp Biopharmaceutical Inc., San Diego, California, USA
| | - Michael Pauly
- Mapp Biopharmaceutical Inc., San Diego, California, USA
| | - Kevin Whaley
- Mapp Biopharmaceutical Inc., San Diego, California, USA
| | - Yinghui Rong
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Fernando J Torres-Velez
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Ellen S Vitetta
- Departments of Immunology and Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Peter J Didier
- Tulane National Primate Research Center (TNPRC), Covington, Louisiana, USA
| | - Lara Doyle-Meyers
- Tulane National Primate Research Center (TNPRC), Covington, Louisiana, USA
| | - Larry Zeitlin
- Mapp Biopharmaceutical Inc., San Diego, California, USA
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
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11
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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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12
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Westfall J, Yates JL, Van Slyke G, Ehrbar D, Measey T, Straube R, Donini O, Mantis NJ. Thermal stability and epitope integrity of a lyophilized ricin toxin subunit vaccine. Vaccine 2018; 36:5967-5976. [PMID: 30172637 PMCID: PMC6320669 DOI: 10.1016/j.vaccine.2018.08.059] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 08/18/2018] [Accepted: 08/23/2018] [Indexed: 12/18/2022]
Abstract
Biodefense vaccine are destined to be stockpiled for periods of time and deployed in the event of a public health emergency. In this report, we compared the potency of liquid and lyophilized (thermostabilized) formulations of a candidate ricin toxin subunit vaccine, RiVax, adsorbed to aluminum salts adjuvant, over a 12-month period. The liquid and lyophilized formulations were stored at stressed (40 °C) and unstressed (4 °C) conditions and evaluated at 3, 6 and 12-month time points for potency in a mouse model of lethal dose ricin challenge. At the same time points, the vaccine formulations were interrogated in vitro by competition ELISA for conformational integrity using a panel of three monoclonal antibodies (mAbs), PB10, WECB2, and SyH7, directed against known immunodominant toxin-neutralizing epitopes on RiVax. We found that the liquid vaccine under stress conditions declined precipitously within the first three months, as evidenced by a reduction in in vivo potency and concomitant loss of mAb recognition in vitro. In contrast, the lyophilized RiVax vaccine retained in vivo potency and conformational integrity for up to one year at 4 °C and 40 °C. We discuss the utility of monitoring the integrity of one or more toxin-neutralizing epitopes on RiVax as a possible supplement to animal studies to assess vaccine potency.
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Affiliation(s)
- Jennifer Westfall
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Jennifer L Yates
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Greta Van Slyke
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Dylan Ehrbar
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | | | | | | | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States.
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13
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Van Slyke G, Angalakurthi SK, Toth RT, Vance DJ, Rong Y, Ehrbar D, Shi Y, Middaugh CR, Volkin DB, Weis DD, Mantis NJ. Fine-Specificity Epitope Analysis Identifies Contact Points on Ricin Toxin Recognized by Protective Monoclonal Antibodies. Immunohorizons 2018; 2:262-273. [PMID: 30766971 DOI: 10.4049/immunohorizons.1800042] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Ricin is a fast-acting protein toxin classified by the Centers for Disease Control and Prevention as a biothreat agent. In this report, we describe five new mouse mAbs directed against an immunodominant region, so-called epitope cluster II, on the surface of ricin's ribosome-inactivating enzymatic subunit A (RTA). The five mAbs were tested alongside four previously described cluster II-specific mAbs for their capacity to passively protect mice against 10× LD50 ricin challenge by injection. Only three of the mAbs (LE4, PH12, and TB12) afforded protection over the 7-d study period. Neither binding affinity nor in vitro toxin-neutralizing activity could fully account for LE4, PH12, and TB12's potent in vivo activity relative to the other six mAbs. However, epitope mapping studies by hydrogen exchange-mass spectrometry revealed that LE4, PH12, and TB12 shared common contact points on RTA corresponding to RTA α-helices D and E and β-strands d and e located on the back side of RTA relative to the active site. The other six mAbs recognized overlapping epitopes on RTA, but none shared the same hydrogen exchange-mass spectrometry profile as LE4, PH12, and TB12. A high-density competition ELISA with a panel of ricin-specific, single-domain camelid Abs indicated that even though LE4, PH12, and TB12 make contact with similar secondary motifs, they likely approach RTA from different angles. These results underscore how subtle differences in epitope specificity can significantly impact Ab functionality in vivo. ImmunoHorizons, 2018, 2: 262-273.
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Affiliation(s)
- Greta Van Slyke
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208
| | - Siva Krishna Angalakurthi
- Macromolecule and Vaccine Stabilization Center, Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS 66045
| | - Ronald T Toth
- Macromolecule and Vaccine Stabilization Center, Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS 66045
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208
| | - Yinghui Rong
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208
| | - Dylan Ehrbar
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208
| | - Yuqi Shi
- Department of Chemistry, University of Kansas, Lawrence, KS 66045
| | - C Russell Middaugh
- Macromolecule and Vaccine Stabilization Center, Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS 66045
| | - David B Volkin
- Macromolecule and Vaccine Stabilization Center, Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS 66045
| | - David D Weis
- Department of Chemistry, University of Kansas, Lawrence, KS 66045
| | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208
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14
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Avril A. Therapeutic Antibodies for Biodefense. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1053:173-205. [PMID: 29549640 DOI: 10.1007/978-3-319-72077-7_9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Diseases can be caused naturally by biological agents such as bacteria, viruses and toxins (natural risk). However, such biological agents can be intentionally disseminated in the environment by a State (military context) or terrorists to cause diseases in a population or livestock, to destabilize a nation by creating a climate of terror, destabilizing the economy and undermining institutions. Biological agents can be classified according to the severity of illness they cause, its mortality and how easily the agent can be spread. The Centers for Diseases Control and Prevention (CDC) classify biological agents in three categories (A, B and C); Category A consists of the six pathogens most suitable for use as bioweapons (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox and viral hemorrhagic fevers). Antibodies represent a perfect biomedical countermeasure as they present both prophylactic and therapeutic properties, act fast and are highly specific to the target. This review focuses on the main biological agents that could be used as bioweapons, the history of biowarfare and antibodies that have been developed to neutralize these agents.
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Affiliation(s)
- Arnaud Avril
- Département des maladies infectieuses, Unité biothérapies anti-infectieuses et immunité, Institut de Recherche Biomédical des Armées, Brétigny-sur-Orge, France.
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15
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Rudolph MJ, Vance DJ, Kelow S, Angalakurthi SK, Nguyen S, Davis SA, Rong Y, Middaugh CR, Weis DD, Dunbrack R, Karanicolas J, Mantis NJ. Contribution of an unusual CDR2 element of a single domain antibody in ricin toxin binding affinity and neutralizing activity. Protein Eng Des Sel 2018; 31:277-287. [PMID: 30265352 PMCID: PMC6277176 DOI: 10.1093/protein/gzy022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 08/03/2018] [Indexed: 11/13/2022] Open
Abstract
Ricin toxin's enzymatic subunit (RTA) has been subjected to intensive B cell epitope mapping studies using a combination of competition ELISAs, hydrogen exchange-mass spectrometry and X-ray crystallography. Those studies identified four spatially distinct clusters (I-IV) of toxin-neutralizing epitopes on the surface of RTA. Here we describe A9, a new single domain camelid antibody (VHH) that was proposed to recognize a novel epitope on RTA that straddles clusters I and III. The X-ray crystal structure of A9 bound to RTA (2.6 Å resolution) revealed extensive antibody contact with RTA's β-strand h (732 Å2 buried surface area; BSA), along with limited engagement with α-helix D (90 Å2) and α-helix C (138 Å2). Collectively, these contacts explain the overlap between epitope clusters I and III, as identified by competition ELISA. However, considerable binding affinity, and, consequently, toxin-neutralizing activity of A9 is mediated by an unusual CDR2 containing five consecutive Gly residues that interact with α-helix B (82 Å2), a known neutralizing hotspot on RTA. Removal of a single Gly residue from the penta-glycine stretch in CDR2 reduced A9's binding affinity by 10-fold and eliminated toxin-neutralizing activity. Computational modeling indicates that removal of a Gly from CDR2 does not perturb contact with RTA per se, but results in the loss of an intramolecular hydrogen bond network involved in stabilizing CDR2 in the unbound state. These results reveal a novel configuration of a CDR2 element involved in neutralizing ricin toxin.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Simon Kelow
- Department of Biochemistry and Molecular Biophysics Graduate Group, University of Pennsylvania, Philadelphia, PA, USA
| | - Siva Krishna Angalakurthi
- Department of Pharmaceutical Chemistry and Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, KS, USA
| | - Sophie Nguyen
- New York Structural Biology Center, New York, NY, USA
| | - Simon A Davis
- New York Structural Biology Center, New York, NY, USA
| | - Yinghui Rong
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - C Russell Middaugh
- Department of Pharmaceutical Chemistry and Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, KS, USA
| | - David D Weis
- Department of Chemistry and Ralph Adams Institute for Bioanalytical Chemistry, University of Kansas, Lawrence, KS, USA
| | - Roland Dunbrack
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA, USA
| | - John Karanicolas
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA, USA
| | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
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16
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Zhou Y, Li XP, Kahn JN, Tumer NE. Functional Assays for Measuring the Catalytic Activity of Ribosome Inactivating Proteins. Toxins (Basel) 2018; 10:toxins10060240. [PMID: 29899209 PMCID: PMC6024586 DOI: 10.3390/toxins10060240] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Revised: 06/01/2018] [Accepted: 06/07/2018] [Indexed: 12/11/2022] Open
Abstract
Ribosome-inactivating proteins (RIPs) are potent toxins that inactivate ribosomes by catalytically removing a specific adenine from the α-sarcin/ricin loop (SRL) of the large rRNA. Direct assays for measuring depurination activity and indirect assays for measuring the resulting translation inhibition have been employed to determine the enzyme activity of RIPs. Rapid and sensitive methods to measure the depurination activity of RIPs are critical for assessing their reaction mechanism, enzymatic properties, interaction with ribosomal proteins, ribotoxic stress signaling, in the search for inhibitors and in the detection and diagnosis of enteric infections. Here, we review the major assays developed for measuring the catalytic activity of RIPs, discuss their advantages and disadvantages and explain how they are used in understanding the catalytic mechanism, ribosome specificity, and dynamic enzymatic features of RIPs.
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Affiliation(s)
- Yijun Zhou
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
| | - Xiao-Ping Li
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
| | - Jennifer N Kahn
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
| | - Nilgun E Tumer
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
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17
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Yates JL, Leadbetter E, Mantis NJ. Alpha-galactosylceramide (αGalCer) enhances vaccine-induced protection in a model of ricin intoxication. Hum Vaccin Immunother 2018; 14:2053-2057. [PMID: 29617191 DOI: 10.1080/21645515.2018.1461299] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Alpha-galactosylceramide (αGalCer) is a glycolipid derived from a marine sponge that is a potent activator of both mouse and human invariant natural killer T (iNKT) cells. For that reason, αGalCer is a promising vaccine adjuvant that has been shown to improve both humoral and cellular immunity when co-administered with various vaccines, including candidate vaccines for biodefense. In the current study, we tested the effectiveness of αGalCer as an adjuvant for the clinically-relevant ricin toxin subunit vaccine, RiVax. αGalCer had a potent adjuvant effect, as shown by a rapid onset of anti-ricin IgG titers, accelerated development of serum toxin-neutralizing activity, and enhanced protection from lethal ricin challenge in a mouse model. These results underscore the potential of αGalCer to augment the protective immune response to a vaccine designed to counteract ricin toxin, a fast-acting biothreat agent.
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Affiliation(s)
- Jennifer L Yates
- a Division of Infectious Disease, Wadsworth Center, New York State Department of Health , Albany , NY
| | - Elizabeth Leadbetter
- b Department of Microbiology, Immunology, and Molecular Genetics , The University of Texas Health Science Center at San Antonio , San Antonio , TX
| | - Nicholas J Mantis
- a Division of Infectious Disease, Wadsworth Center, New York State Department of Health , Albany , NY
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18
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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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19
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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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20
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Plant Ribosome-Inactivating Proteins: Progesses, Challenges and Biotechnological Applications (and a Few Digressions). Toxins (Basel) 2017; 9:toxins9100314. [PMID: 29023422 PMCID: PMC5666361 DOI: 10.3390/toxins9100314] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 09/29/2017] [Accepted: 10/03/2017] [Indexed: 12/11/2022] Open
Abstract
Plant ribosome-inactivating protein (RIP) toxins are EC3.2.2.22 N-glycosidases, found among most plant species encoded as small gene families, distributed in several tissues being endowed with defensive functions against fungal or viral infections. The two main plant RIP classes include type I (monomeric) and type II (dimeric) as the prototype ricin holotoxin from Ricinus communis that is composed of a catalytic active A chain linked via a disulphide bridge to a B-lectin domain that mediates efficient endocytosis in eukaryotic cells. Plant RIPs can recognize a universally conserved stem-loop, known as the α-sarcin/ ricin loop or SRL structure in 23S/25S/28S rRNA. By depurinating a single adenine (A4324 in 28S rat rRNA), they can irreversibly arrest protein translation and trigger cell death in the intoxicated mammalian cell. Besides their useful application as potential weapons against infected/tumor cells, ricin was also used in bio-terroristic attacks and, as such, constitutes a major concern. In this review, we aim to summarize past studies and more recent progresses made studying plant RIPs and discuss successful approaches that might help overcoming some of the bottlenecks encountered during the development of their biomedical applications.
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21
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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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22
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Rudolph MJ, Vance DJ, Cassidy MS, Rong Y, Mantis NJ. Structural Analysis of Single Domain Antibodies Bound to a Second Neutralizing Hot Spot on Ricin Toxin's Enzymatic Subunit. J Biol Chem 2017; 292:872-883. [PMID: 27903650 PMCID: PMC5247660 DOI: 10.1074/jbc.m116.758102] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 11/10/2016] [Indexed: 12/15/2022] Open
Abstract
Ricin toxin is a heterodimer consisting of RTA, a ribosome-inactivating protein, and RTB, a lectin that facilitates receptor-mediated uptake into mammalian cells. In previous studies, we demonstrated that toxin-neutralizing antibodies target four spatially distinct hot spots on RTA, which we refer to as epitope clusters I-IV. In this report, we identified and characterized three single domain camelid antibodies (VHH) against cluster II. One of these VHHs, V5E1, ranks as one of the most potent ricin-neutralizing antibodies described to date. We solved the X-ray crystal structures of each of the three VHHs (E1, V1C7, and V5E1) in complex with RTA. V5E1 buries a total of 1,133 Å2 of surface area on RTA and makes primary contacts with α-helix A (residues 18-32), α-helix F (182-194), as well as the F-G loop. V5E1, by virtue of complementarity determining region 3 (CDR3), may also engage with RTB and potentially interfere with the high affinity galactose-recognition element that plays a critical role in toxin attachment to cell surfaces and intracellular trafficking. The two other VHHs, E1 and V1C7, bind epitopes adjacent to V5E1 but display only weak toxin neutralizing activity, thereby providing structural insights into specific residues within cluster II that may be critical contact points for toxin inactivation.
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Affiliation(s)
- Michael J Rudolph
- From the New York Structural Biology Center, New York, New York 10027,
| | - David J Vance
- the Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, New York 12208, and
| | - Michael S Cassidy
- From the New York Structural Biology Center, New York, New York 10027
| | - Yinghui Rong
- the Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, New York 12208, and
| | - Nicholas J Mantis
- the Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, New York 12208, and
- the Department of Biomedical Sciences, University at Albany, Albany, New York 12201
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23
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Rudolph MJ, Vance DJ, Cassidy MS, Rong Y, Shoemaker CB, Mantis NJ. Structural analysis of nested neutralizing and non-neutralizing B cell epitopes on ricin toxin's enzymatic subunit. Proteins 2016; 84:1162-72. [PMID: 27159829 DOI: 10.1002/prot.25062] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Revised: 03/31/2016] [Accepted: 04/28/2016] [Indexed: 11/10/2022]
Abstract
In this report, we describe the X-ray crystal structures of two single domain camelid antibodies (VH H), F5 and F8, each in complex with ricin toxin's enzymatic subunit (RTA). F5 has potent toxin-neutralizing activity, while F8 has weak neutralizing activity. F5 buried a total of 1760 Å(2) in complex with RTA and made contact with three prominent secondary structural elements: α-helix B (Residues 98-106), β-strand h (Residues 113-117), and the C-terminus of α-helix D (Residues 154-156). F8 buried 1103 Å(2) in complex with RTA that was centered primarily on β-strand h. As such, the structural epitope of F8 is essentially nested within that of F5. All three of the F5 complementarity determining regions CDRs were involved in RTA contact, whereas F8 interactions were almost entirely mediated by CDR3, which essentially formed a seventh β-strand within RTA's centrally located β-sheet. A comparison of the two structures reported here to several previously reported (RTA-VH H) structures identifies putative contact sites on RTA, particularly α-helix B, associated with potent toxin-neutralizing activity. This information has implications for rational design of RTA-based subunit vaccines for biodefense. Proteins 2016; 84:1162-1172. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, New York State Department of Health, Wadsworth Center, Albany, New York, 12208
| | | | - Yinghui Rong
- Division of Infectious Diseases, New York State Department of Health, Wadsworth Center, Albany, New York, 12208
| | - Charles B Shoemaker
- Tufts Cummings School of Veterinary Medicine, North Grafton, Massachusetts, 01536
| | - Nicholas J Mantis
- Division of Infectious Diseases, New York State Department of Health, Wadsworth Center, Albany, New York, 12208.,Department of Biomedical Sciences, University at Albany, Albany, New York, 12201
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