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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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Alcalay R, Falach R, Gal Y, Sapoznikov A, Sabo T, Kronman C, Mazor O. Mapping Immunodominant Antibody Epitopes of Abrin. Antibodies (Basel) 2020; 9:antib9020011. [PMID: 32349421 PMCID: PMC7344891 DOI: 10.3390/antib9020011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2020] [Revised: 04/21/2020] [Accepted: 04/22/2020] [Indexed: 11/22/2022] Open
Abstract
Abrin, a toxin isolated from the seeds of Abrus precatorius (jequirity pea) is considered a biological threat agent by the Center for Disease Control and Prevention. To date, there is no effective postexposure treatment for abrin poisoning, and efforts are being made to develop an efficient vaccine and measures for postexposure therapy. Epitope mapping is widely applied as an efficient tool for discovering the antigenic moieties of toxins, thus providing invaluable information needed for the development of vaccines and therapies. Aiming to identify the immunodominant epitopes of abrin, several neutralizing antiabrin polyclonal antibodies were screened using a set of 15-mer peptides spanning the amino acid sequence of either the A or B subunits of abrin. Analysis of the antibody-binding pattern revealed 11 linear epitopes for the A subunit and 14 epitopes for the B subunit that are located on the surface of the toxin and thus accessible for antibody interactions. Moreover, the spatial location of several of these epitopes suggests they may block the galactose-binding pockets or the catalytic domain, thus neutralizing the toxin. These findings provide useful information and suggest a possible strategy for the development and design of an improved abrin-based vaccine and therapeutic antibodies.
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Affiliation(s)
- Ron Alcalay
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel; (R.A.); (R.F.); (Y.G.); (A.S.); (T.S.); (C.K.)
| | - Reut Falach
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel; (R.A.); (R.F.); (Y.G.); (A.S.); (T.S.); (C.K.)
| | - Yoav Gal
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel; (R.A.); (R.F.); (Y.G.); (A.S.); (T.S.); (C.K.)
| | - Anita Sapoznikov
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel; (R.A.); (R.F.); (Y.G.); (A.S.); (T.S.); (C.K.)
| | - Tamar Sabo
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel; (R.A.); (R.F.); (Y.G.); (A.S.); (T.S.); (C.K.)
| | - Chanoch Kronman
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel; (R.A.); (R.F.); (Y.G.); (A.S.); (T.S.); (C.K.)
| | - Ohad Mazor
- Department of Infectious Diseases, Israel Institute for Biological Research, Ness-Ziona 76100, Israel
- Correspondence: ; Tel.: +972-8-9385862; Fax: +972-8-9381544
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Equal Neutralization Potency of Antibodies Raised against Abrin Subunits. Antibodies (Basel) 2020; 9:antib9010004. [PMID: 32041179 PMCID: PMC7148520 DOI: 10.3390/antib9010004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Revised: 01/22/2020] [Accepted: 01/25/2020] [Indexed: 11/17/2022] Open
Abstract
Abrin and ricin are potent AB toxins, which are considered biological threats. To date, there are no approved treatments against abrin or ricin intoxications. Previously, we showed that the administration of polyclonal anti-abrin antibodies to mice that were intranasally exposed to abrin, even very late post-exposure, conferred an exceedingly high-level of protection, while following ricin intoxication, similar treatment with anti-ricin antibodies resulted in negligible survival rates. To probe this unexpected difference in protection ability, we first examined whether the efficient anti-abrin-induced protection was due to neutralization of the A-subunit responsible for the catalytic effect, or of the B-subunit, which enables binding/internalization, by evaluating the protection conferred by antibodies directed against one of the two subunits. To this end, we generated and immunized rabbits with chimeric toxins containing a single abrin subunit, AabrinBricin in which abrin A-subunit was linked to ricin B-subunit, and AricinBabrin in which ricin A-subunit is linked to abrin B-subunit. Here, we show that antibodies raised against either AabrinBricin or AricinBabrin conferred exceptionally high protection levels to mice following intranasal exposure to a a lethal dose of abrin, suggesting that the high level of protection conferred by anti-abrin antibodies is not related to the neutralization of a particular subunit.
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Generation of Highly Efficient Equine-Derived Antibodies for Post-Exposure Treatment of Ricin Intoxications by Vaccination with Monomerized Ricin. Toxins (Basel) 2018; 10:toxins10110466. [PMID: 30424519 PMCID: PMC6267474 DOI: 10.3390/toxins10110466] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 11/04/2018] [Accepted: 11/08/2018] [Indexed: 12/13/2022] Open
Abstract
Ricin, a highly lethal toxin derived from the seeds of Ricinus communis (castor beans) is considered a potential biological threat agent due to its high availability, ease of production, and to the lack of any approved medical countermeasure against ricin exposures. To date, the use of neutralizing antibodies is the most promising post-exposure treatment for ricin intoxication. The aim of this work was to generate anti-ricin antitoxin that confers high level post-exposure protection against ricin challenge. Due to safety issues regarding the usage of ricin holotoxin as an antigen, we generated an inactivated toxin that would reduce health risks for both the immunizer and the immunized animal. To this end, a monomerized ricin antigen was constructed by reducing highly purified ricin to its monomeric constituents. Preliminary immunizing experiments in rabbits indicated that this monomerized antigen is as effective as the native toxin in terms of neutralizing antibody elicitation and protection of mice against lethal ricin challenges. Characterization of the monomerized antigen demonstrated that the irreversibly detached A and B subunits retain catalytic and lectin activity, respectively, implying that the monomerization process did not significantly affect their overall structure. Toxicity studies revealed that the monomerized ricin displayed a 250-fold decreased activity in a cell culture-based functionality test, while clinical signs were undetectable in mice injected with this antigen. Immunization of a horse with the monomerized toxin was highly effective in elicitation of high titers of neutralizing antibodies. Due to the increased potential of IgG-derived adverse events, anti-ricin F(ab')₂ antitoxin was produced. The F(ab')₂-based antitoxin conferred high protection to intranasally ricin-intoxicated mice; ~60% and ~34% survival, when administered 24 and 48 h post exposure to a lethal dose, respectively. In line with the enhanced protection, anti-inflammatory and anti-edematous effects were measured in the antitoxin treated mice, in comparison to mice that were intoxicated but not treated. Accordingly, this anti-ricin preparation is an excellent candidate for post exposure treatment of ricin intoxications.
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Noy-Porat T, Rosenfeld R, Ariel N, Epstein E, Alcalay R, Zvi A, Kronman C, Ordentlich A, Mazor O. Isolation of Anti-Ricin Protective Antibodies Exhibiting High Affinity from Immunized Non-Human Primates. Toxins (Basel) 2016; 8:toxins8030064. [PMID: 26950154 PMCID: PMC4810209 DOI: 10.3390/toxins8030064] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 02/25/2016] [Accepted: 02/26/2016] [Indexed: 11/16/2022] Open
Abstract
Ricin, derived from the castor bean plant Ricinus communis, is one of the most potent and lethal toxins known, against which there is no available antidote. To date, the use of neutralizing antibodies is the most promising post-exposure treatment for ricin intoxication. The aim of this study was to isolate high affinity anti-ricin antibodies that possess potent toxin-neutralization capabilities. Two non-human primates were immunized with either a ricin-holotoxin- or subunit-based vaccine, to ensure the elicitation of diverse high affinity antibodies. By using a comprehensive set of primers, immune scFv phage-displayed libraries were constructed and panned. A panel of 10 antibodies (five directed against the A subunit of ricin and five against the B subunit) was isolated and reformatted into a full-length chimeric IgG. All of these antibodies were found to neutralize ricin in vitro, and several conferred full protection to ricin-intoxicated mice when given six hours after exposure. Six antibodies were found to possess exceptionally high affinity toward the toxin, with KD values below pM (koff < 1 × 10−7 s−1) that were well correlated with their ability to neutralize ricin. These antibodies, alone or in combination, could be used for the development of a highly-effective therapeutic preparation for post-exposure treatment of ricin intoxication.
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Affiliation(s)
- Tal Noy-Porat
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ronit Rosenfeld
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Naomi Ariel
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Eyal Epstein
- Department of Biotechnology, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ron Alcalay
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Anat Zvi
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Chanoch Kronman
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Arie Ordentlich
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ohad Mazor
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
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