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Ricin toxin and its neutralizing antibodies: A review. Toxicon 2022; 214:47-53. [PMID: 35595086 DOI: 10.1016/j.toxicon.2022.05.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Revised: 05/10/2022] [Accepted: 05/13/2022] [Indexed: 11/22/2022]
Abstract
Ricin toxin (RT) belongs to the ribosome-inactivating protein (RIP) family of toxins and is considered to be a moderate threat by the US Center of Disease Control and Prevention (CDC). RT poses a great potential threat to the public, but there has been a lack of effective treatment options so far. Over the past few decades, researches on the prevention and treatment of RT poisoning have been investigated, among which neutralizing antibodies targeting RT specifically have always been a research hotspot. In this review, we have summarized the mechanism of action of RT, the research results and the design strategies of RT neutralizing antibodies, and discussed the key issues in the development of RT neutralizing antibody researches.
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2
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Bansia H, Bagaria S, Karande AA, Ramakumar S. Structural basis for neutralization of cytotoxic abrin by monoclonal antibody D6F10. FEBS J 2019; 286:1003-1029. [DOI: 10.1111/febs.14716] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Revised: 11/02/2018] [Accepted: 11/30/2018] [Indexed: 11/26/2022]
Affiliation(s)
- Harsh Bansia
- Department of Physics Indian Institute of Science Bengaluru India
| | - Shradha Bagaria
- Department of Biochemistry Indian Institute of Science Bengaluru India
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3
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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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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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5
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Lenz SAP, Kohout JD, Wetmore SD. Hydrolytic Glycosidic Bond Cleavage in RNA Nucleosides: Effects of the 2'-Hydroxy Group and Acid-Base Catalysis. J Phys Chem B 2016; 120:12795-12806. [PMID: 27933981 DOI: 10.1021/acs.jpcb.6b09620] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Despite the inherent stability of glycosidic linkages in nucleic acids that connect the nucleobases to sugar-phosphate backbones, cleavage of these bonds is often essential for organism survival. The current study uses DFT (B3LYP) to provide a fundamental understanding of the hydrolytic deglycosylation of the natural RNA nucleosides (A, C, G, and U), offers a comparison to DNA hydrolysis, and examines the effects of acid, base, or simultaneous acid-base catalysis on RNA deglycosylation. By initially examining HCOO-···H2O mediated deglycosylation, the barriers for RNA hydrolysis were determined to be 30-38 kJ mol-1 higher than the corresponding DNA barriers, indicating that the 2'-OH group stabilizes the glycosidic bond. Although the presence of HCOO- as the base (i.e., to activate the water nucleophile) reduces the barrier for uncatalyzed RNA hydrolysis (i.e., unactivated H2O nucleophile) by ∼15-20 kJ mol-1, the extreme of base catalysis as modeled using a fully deprotonated water molecule (i.e., OH- nucleophile) decreases the uncatalyzed barriers by up to 65 kJ mol-1. Acid catalysis was subsequently examined by selectively protonating the hydrogen-bond acceptor sites of the RNA nucleobases, which results in an up to ∼80 kJ mol-1 barrier reduction relative to the corresponding uncatalyzed pathway. Interestingly, the nucleobase proton acceptor sites that result in the greatest barrier reductions match sites typically targeted in enzyme-catalyzed reactions. Nevertheless, simultaneous acid and base catalysis is the most beneficial way to enhance the reactivity of the glycosidic bonds in RNA, with the individual effects of each catalytic approach being weakened, additive, or synergistic depending on the strength of the base (i.e., degree of water nucleophile activation), the nucleobase, and the hydrogen-bonding acceptor site on the nucleobase. Together, the current contribution provides a greater understanding of the reactivity of the glycosidic bond in natural RNA nucleosides, and has fundamental implications for the function of RNA-targeting enzymes.
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Affiliation(s)
- Stefan A P Lenz
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Johnathan D Kohout
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Stacey D Wetmore
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
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6
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Jetzt AE, Li XP, Tumer NE, Cohick WS. Toxicity of ricin A chain is reduced in mammalian cells by inhibiting its interaction with the ribosome. Toxicol Appl Pharmacol 2016; 310:120-128. [PMID: 27639428 DOI: 10.1016/j.taap.2016.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 09/08/2016] [Accepted: 09/10/2016] [Indexed: 01/11/2023]
Abstract
Ricin is a potent ribotoxin that is considered a bioterror threat due to its ease of isolation and possibility of aerosolization. In yeast, mutation of arginine residues away from the active site results in a ricin toxin A chain (RTA) variant that is unable to bind the ribosome and exhibits reduced cytotoxicity. The goal of the present work was to determine if these residues contribute to ribosome binding and cytotoxicity of RTA in mammalian cells. The RTA mutant R193A/R235A did not interact with mammalian ribosomes, while a G212E variant with a point mutation near its active site bound ribosomes similarly to wild-type (WT) RTA. R193A/R235A retained full catalytic activity on naked RNA but had reduced activity on mammalian ribosomes. To determine the effect of this mutant in intact cells, pre R193A/R235A containing a signal sequence directing it to the endoplasmic reticulum and mature R193A/R235A that directly targeted cytosolic ribosomes were each expressed. Depurination and protein synthesis inhibition were reduced by both pre- and mature R193A/R235A relative to WT. Protein synthesis inhibition was reduced to a greater extent by R193A/R235A than by G212E. Pre R193A/R235A caused a greater reduction in caspase activation and loss of mitochondrial membrane potential than G212E relative to WT RTA. These findings indicate that an RTA variant with reduced ribosome binding is less toxic than a variant with less catalytic activity but normal ribosome binding activity. The toxin-ribosome interaction represents a novel target for the development of therapeutics to prevent or treat ricin intoxication.
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Affiliation(s)
- Amanda E Jetzt
- Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States
| | - Xiao-Ping Li
- Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States
| | - Nilgun E Tumer
- Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States
| | - Wendie S Cohick
- Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States.
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7
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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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8
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Zhao YQ, Song J, Wang HL, Xu B, Liu F, He K, Wang N. Rapid Detection of Ricin in Serum Based on Cu-Chelated Magnetic Beads Using Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:748-751. [PMID: 26873724 DOI: 10.1007/s13361-016-1340-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 01/02/2016] [Accepted: 01/09/2016] [Indexed: 06/05/2023]
Abstract
The protein toxin ricin obtained from castor bean plant (Ricinus communis) seeds is a potent biological warfare agent due to its ease of availability and acute toxicity. In this study, we demonstrated a rapid and simple method to detect ricin in serum in vitro. The ricin was mixed with serum and digested by trypsin, then all the peptides were efficiently extracted using Cu-chelated magnetic beads and were detected with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The specific ricin peptides were identified by Nanoscale Ultra Performance liquid chromatography coupled to tandem mass spectrometry according to their sequences. The assay required 2.5 hours, and a characteristic peptide could be detected down to 4 ng/μl and used as a biomarker to detect ricin in serum. The high sensitivity and simplicity of the procedure makes it valuable in clinical practice. Graphical Abstract ᅟ.
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Affiliation(s)
- Yong-Qiang Zhao
- The Institute of Basic Medical Sciences, National Center of Biomedical Analysis, Beijing, China, 100850
| | - Jian Song
- The School of Pharmacy, Jilin University, Changchun, China, 130021
| | - Hong-Li Wang
- The Institute of Basic Medical Sciences, National Center of Biomedical Analysis, Beijing, China, 100850
| | - Bin Xu
- The Institute of Basic Medical Sciences, National Center of Biomedical Analysis, Beijing, China, 100850
| | - Feng Liu
- The Institute of Basic Medical Sciences, National Center of Biomedical Analysis, Beijing, China, 100850
| | - Kun He
- The Institute of Basic Medical Sciences, National Center of Biomedical Analysis, Beijing, China, 100850.
| | - Na Wang
- The Institute of Basic Medical Sciences, National Center of Biomedical Analysis, Beijing, China, 100850.
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9
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Akkouh O, Ng TB, Cheung RCF, Wong JH, Pan W, Ng CCW, Sha O, Shaw PC, Chan WY. Biological activities of ribosome-inactivating proteins and their possible applications as antimicrobial, anticancer, and anti-pest agents and in neuroscience research. Appl Microbiol Biotechnol 2015; 99:9847-63. [PMID: 26394859 DOI: 10.1007/s00253-015-6941-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Revised: 08/10/2015] [Accepted: 08/13/2015] [Indexed: 02/06/2023]
Abstract
Ribosome-inactivating proteins (RIPs) are enzymes which depurinate ribosomal RNA (rRNA), thus impeding the process of translation resulting in inhibition of protein synthesis. They are produced by various organisms including plants, fungi and bacteria. RIPs from plants are linked to plant defense due to their antiviral, antifungal, antibacterial, and insecticidal activities in which they can be applied in agriculture to combat microbial pathogens and pests. Their anticancer, antiviral, embryotoxic, and abortifacient properties may find medicinal applications. Besides, conjugation of RIPs with antibodies or other carriers to form immunotoxins has been found useful to research in neuroscience and anticancer therapy.
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Affiliation(s)
- Ouafae Akkouh
- Department of Biology and Medical Laboratory Research, Faculty of Technology, University of Applied Sciences Leiden, Zernikdreef 11, 2333 CK, Leiden, The Netherlands.
| | - Tzi Bun Ng
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
| | - Randy Chi Fai Cheung
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
| | - Jack Ho Wong
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
| | - Wenliang Pan
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
| | - Charlene Cheuk Wing Ng
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
| | - Ou Sha
- School of Medicine, Shenzhen University Health Science Centre, Shenzhen University, Shenzhen, China.
| | - Pang Chui Shaw
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
| | - Wai Yee Chan
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
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10
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Dong J, Zhang Y, Chen Y, Niu X, Zhang Y, Li R, Yang C, Wang Q, Li X, Deng X. Baicalin inhibits the lethality of ricin in mice by inducing protein oligomerization. J Biol Chem 2015; 290:12899-907. [PMID: 25847243 DOI: 10.1074/jbc.m114.632828] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Indexed: 12/11/2022] Open
Abstract
Toxic ribosome-inactivating proteins abolish cell viability by inhibiting protein synthesis. Ricin, a member of these lethal proteins, is a potential bioterrorism agent. Despite the grave challenge posed by these toxins to public health, post-exposure treatment for intoxication caused by these agents currently is unavailable. In this study, we report the identification of baicalin extracted from Chinese herbal medicine as a compound capable of inhibiting the activity of ricin. More importantly, post-exposure treatment with baicalin significantly increased the survival of mice poisoned by ricin. We determined the mechanism of action of baicalin by solving the crystal structure of its complex with the A chain of ricin (RTA) at 2.2 Å resolution, which revealed that baicalin interacts with two RTA molecules at a novel binding site by hydrogen bond networks and electrostatic force interactions, suggesting its role as molecular glue of the RTA. Further biochemical and biophysical analyses validated the amino acids directly involved in binding the inhibitor, which is consistent with the hypothesis that baicalin exerts its inhibitory effects by inducing RTA to form oligomers in solution, a mechanism that is distinctly different from previously reported inhibitors. This work offers promising leads for the development of therapeutics against ricin and probably other ribosome-inactivating proteins.
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Affiliation(s)
- Jing Dong
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062, the Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223
| | - Yong Zhang
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062
| | - Yutao Chen
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101
| | - Xiaodi Niu
- the Department of Food Quality and Safety, Jilin University, Changchun 130062, and
| | - Yu Zhang
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062
| | - Rui Li
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062
| | - Cheng Yang
- the College of Pharmacy, NanKai University, Tianjin 300071, China
| | - Quan Wang
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101
| | - Xuemei Li
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101,
| | - Xuming Deng
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062,
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11
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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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