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Liu XY, Wei DK, Li ZY, Lu JS, Xie XM, Yu YZ, Pang XB. Immunogenicity and immunoprotection of the functional TL-HN fragment derived from tetanus toxin. Vaccine 2023; 41:6834-6841. [PMID: 37816654 DOI: 10.1016/j.vaccine.2023.09.032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 09/11/2023] [Accepted: 09/18/2023] [Indexed: 10/12/2023]
Abstract
Tetanus toxin (TeNT) is a protein toxin produced by Clostridium tetani bacteria, which causes hyperreflexia and rhabdomyolysis by spastic paralysis. Like botulinum neurotoxin, TeNT comprises a heavy chain (HC) and a light chain (LC) linked via an interchain disulfide bond, which include the following three functional domains: a receptor-binding domain (Hc), a translocation domain (HN), and a catalytic domain (LC). Herein, we produced and characterized three functional domains of TeNT and three types of TeNT-derived L-HN fragments (TL-HN, TL-GS-HN and TL-2A-HN), which contained L and HN domains but lacked the Hc domain. The immunological effects of these different functional domains or fragments of TeNT were explored in an animal model. Our investigations showed the TL-HN functional fragment provided the best immunoprotection among all the TeNT functional domains. The TL-HN fragment, as a protective antigen, induced the highest levels of neutralizing antibodies, indicating that it might contain some crucial epitopes. Further experiments revealed that the protective effect of TL-HN was superior to that of the THc, TL, or THN fragments, either individually or in combination. Therefore, the TL-HN fragment exerts an important function in immune protection against tetanus toxin, providing a good basis for the development of TeNT vaccines or antibodies, and could serve as a promising subunit vaccine to replace THc or tetanus toxoid (TT).
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Affiliation(s)
- Xu-Yang Liu
- Pharmaceutical College, Henan University, Kaifeng 475001, China; Beijing Institute of Biotechnology, Beijing 100071, China
| | - Dong-Kui Wei
- Pharmaceutical College, Henan University, Kaifeng 475001, China; Beijing Institute of Biotechnology, Beijing 100071, China
| | - Zhi-Ying Li
- Pharmaceutical College, Henan University, Kaifeng 475001, China; Beijing Institute of Biotechnology, Beijing 100071, China
| | - Jian-Sheng Lu
- Beijing Institute of Biotechnology, Beijing 100071, China
| | - Xin-Mei Xie
- Pharmaceutical College, Henan University, Kaifeng 475001, China.
| | - Yun-Zhou Yu
- Beijing Institute of Biotechnology, Beijing 100071, China.
| | - Xiao-Bin Pang
- Pharmaceutical College, Henan University, Kaifeng 475001, China.
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Gupta S, Pellett S. Recent Developments in Vaccine Design: From Live Vaccines to Recombinant Toxin Vaccines. Toxins (Basel) 2023; 15:563. [PMID: 37755989 PMCID: PMC10536331 DOI: 10.3390/toxins15090563] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 08/28/2023] [Accepted: 08/31/2023] [Indexed: 09/28/2023] Open
Abstract
Vaccines are one of the most effective strategies to prevent pathogen-induced illness in humans. The earliest vaccines were based on live inoculations with low doses of live or related pathogens, which carried a relatively high risk of developing the disease they were meant to prevent. The introduction of attenuated and killed pathogens as vaccines dramatically reduced these risks; however, attenuated live vaccines still carry a risk of reversion to a pathogenic strain capable of causing disease. This risk is completely eliminated with recombinant protein or subunit vaccines, which are atoxic and non-infectious. However, these vaccines require adjuvants and often significant optimization to induce robust T-cell responses and long-lasting immune memory. Some pathogens produce protein toxins that cause or contribute to disease. To protect against the effects of such toxins, chemically inactivated toxoid vaccines have been found to be effective. Toxoid vaccines are successfully used today at a global scale to protect against tetanus and diphtheria. Recent developments for toxoid vaccines are investigating the possibilities of utilizing recombinant protein toxins mutated to eliminate biologic activity instead of chemically inactivated toxins. Finally, one of the most contemporary approaches toward vaccine design utilizes messenger RNA (mRNA) as a vaccine candidate. This approach was used globally to protect against coronavirus disease during the COVID-19 pandemic that began in 2019, due to its advantages of quick production and scale-up, and effectiveness in eliciting a neutralizing antibody response. Nonetheless, mRNA vaccines require specialized storage and transport conditions, posing challenges for low- and middle-income countries. Among multiple available technologies for vaccine design and formulation, which technology is most appropriate? This review focuses on the considerable developments that have been made in utilizing diverse vaccine technologies with a focus on vaccines targeting bacterial toxins. We describe how advancements in vaccine technology, combined with a deeper understanding of pathogen-host interactions, offer exciting and promising avenues for the development of new and improved vaccines.
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Affiliation(s)
| | - Sabine Pellett
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA;
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Li Z, Li B, Lu J, Liu X, Tan X, Wang R, Du P, Yu S, Xu Q, Pang X, Yu Y, Yang Z. Biological and Immunological Characterization of a Functional L-HN Derivative of Botulinum Neurotoxin Serotype F. Toxins (Basel) 2023; 15:toxins15030200. [PMID: 36977091 PMCID: PMC10056376 DOI: 10.3390/toxins15030200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2023] [Revised: 03/02/2023] [Accepted: 03/03/2023] [Indexed: 03/08/2023] Open
Abstract
Botulinum neurotoxins (BoNTs) can cause nerve paralysis syndrome in mammals and other vertebrates. BoNTs are the most toxic biotoxins known and are classified as Class A biological warfare agents. BoNTs are mainly divided into seven serotypes A-G and new neurotoxins BoNT/H and BoNT/X, which have similar functions. BoNT proteins are 150 kDa polypeptide consisting of two chains and three domains: the light chain (L, catalytic domain, 50 kDa) and the heavy chain (H, 100 kDa), which can be divided into an N-terminal membrane translocation domain (HN, 50 kDa) and a C-terminal receptor binding domain (Hc, 50 kDa). In current study, we explored the immunoprotective efficacy of each functional molecule of BoNT/F and the biological characteristics of the light chain-heavy N-terminal domain (FL-HN). The two structure forms of FL-HN (i.e., FL-HN-SC: single chain FL-HN and FL-HN-DC: di-chain FL-HN) were developed and identified. FL-HN-SC could cleave the vesicle associated membrane protein 2 (VAMP2) substrate protein in vitro as FL-HN-DC or FL. While only FL-HN-DC had neurotoxicity and could enter neuro-2a cells to cleave VAMP2. Our results showed that the FL-HN-SC had a better immune protection effect than the Hc of BoNT/F (FHc), which indicated that L-HN-SC, as an antigen, provided the strongest protective effects against BoNT/F among all the tested functional molecules. Further in-depth research on the different molecular forms of FL-HN suggested that there were some important antibody epitopes at the L-HN junction of BoNT/F. Thus, FL-HN-SC could be used as a subunit vaccine to replace the FHc subunit vaccine and/or toxoid vaccine, and to develop antibody immune molecules targeting L and HN domains rather than the FHc domain. FL-HN-DC could be used as a new functional molecule to evaluate and explore the structure and activity of toxin molecules. Further exploration of the biological activity and molecular mechanism of the functional FL-HN or BoNT/F is warranted.
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Affiliation(s)
- Zhiying Li
- Beijing Institute of Biotechnology, Beijing 100071, China
- Pharmaceutical College, Henan University, Kaifeng 475001, China
| | - Bolin Li
- Beijing Institute of Biotechnology, Beijing 100071, China
| | - Jiansheng Lu
- Beijing Institute of Biotechnology, Beijing 100071, China
| | - Xuyang Liu
- Beijing Institute of Biotechnology, Beijing 100071, China
- Pharmaceutical College, Henan University, Kaifeng 475001, China
| | - Xiao Tan
- Beijing Institute of Biotechnology, Beijing 100071, China
- Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing 100044, China
| | - Rong Wang
- Beijing Institute of Biotechnology, Beijing 100071, China
| | - Peng Du
- Beijing Institute of Biotechnology, Beijing 100071, China
| | - Shuo Yu
- Beijing Institute of Biotechnology, Beijing 100071, China
| | - Qing Xu
- Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing 100044, China
| | - Xiaobin Pang
- Pharmaceutical College, Henan University, Kaifeng 475001, China
| | - Yunzhou Yu
- Beijing Institute of Biotechnology, Beijing 100071, China
- Correspondence: (Y.Y.); (Z.Y.)
| | - Zhixin Yang
- Beijing Institute of Biotechnology, Beijing 100071, China
- Correspondence: (Y.Y.); (Z.Y.)
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Li Z, Lu J, Tan X, Wang R, Xu Q, Yu Y, Yang Z. Functional EL-HN Fragment as a Potent Candidate Vaccine for the Prevention of Botulinum Neurotoxin Serotype E. Toxins (Basel) 2022; 14:toxins14020135. [PMID: 35202162 PMCID: PMC8880310 DOI: 10.3390/toxins14020135] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 02/08/2022] [Accepted: 02/10/2022] [Indexed: 11/21/2022] Open
Abstract
Clostridium botulinum produces botulinum neurotoxin (BoNT), which is the most toxic known protein and the causative agent of human botulism. BoNTs have similar structures and functions, comprising three functional domains: catalytic domain (L), translocation domain (HN), and receptor-binding domain (Hc). In the present study, BoNT/E was selected as a model toxin to further explore the immunological significance of each domain. The EL-HN fragment (L and HN domains of BoNT/E) retained the enzymatic activity without in vivo neurotoxicity. Extensive investigations showed EL-HN functional fragment had the highest protective efficacy and contained some functional neutralizing epitopes. Further experiments demonstrated the EL-HN provided a superior protective effect compared with the EHc or EHc and EL-HN combination. Thus, the EL-HN played an important role in immune protection against BoNT/E and could provide an excellent platform for the design of botulinum vaccines and neutralizing antibodies. The EL-HN has the potential to replace EHc or toxoid as the optimal immunogen for the botulinum vaccine.
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Affiliation(s)
- Zhen Li
- Beijing Institute of Biotechnology, Beijing 100071, China; (Z.L.); (J.L.); (X.T.); (R.W.)
- Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing 100044, China
| | - Jiansheng Lu
- Beijing Institute of Biotechnology, Beijing 100071, China; (Z.L.); (J.L.); (X.T.); (R.W.)
| | - Xiao Tan
- Beijing Institute of Biotechnology, Beijing 100071, China; (Z.L.); (J.L.); (X.T.); (R.W.)
- Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing 100044, China
| | - Rong Wang
- Beijing Institute of Biotechnology, Beijing 100071, China; (Z.L.); (J.L.); (X.T.); (R.W.)
| | - Qing Xu
- Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing 100044, China
- Correspondence: (Q.X.); (Y.Y.); (Z.Y.)
| | - Yunzhou Yu
- Beijing Institute of Biotechnology, Beijing 100071, China; (Z.L.); (J.L.); (X.T.); (R.W.)
- Correspondence: (Q.X.); (Y.Y.); (Z.Y.)
| | - Zhixin Yang
- Beijing Institute of Biotechnology, Beijing 100071, China; (Z.L.); (J.L.); (X.T.); (R.W.)
- Correspondence: (Q.X.); (Y.Y.); (Z.Y.)
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IŞIK M, BİLİCİ Z, ÇİNE N, ÖZTÜRK S. Usage of Peptide Antigens for Antibody-Based BoNT Detection System. KOCAELI ÜNIVERSITESI SAĞLIK BILIMLERI DERGISI 2021. [DOI: 10.30934/kusbed.935903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Li Z, Lu JS, Liu S, Wang R, Xu Q, Yu YZ, Yang ZX. Recombinant L-HN Fusion Antigen Derived from the L and HN Domains of Botulinum Neurotoxin B Stimulates a Protective Antibody Response Against Active Neurotoxin. Neurotox Res 2021; 39:1044-1053. [PMID: 33616873 DOI: 10.1007/s12640-021-00337-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 01/25/2021] [Accepted: 01/27/2021] [Indexed: 01/04/2023]
Abstract
Botulinum neurotoxin (BoNT) is a neurotoxin produced by Clostridium botulinum in an anaerobic environment. BoNT is the most toxic protein among bacteria, animals, plants, and chemical substances reported to date. BoNTs are 150 kDa proteins composed of three major functional domains: catalytic (L domain, 50 kDa), translocation (HN domain, 50 kDa), and receptor-binding (Hc domain, 50 kDa) domains. Most studies have focused on the use of the Hc domain as an antigen because it is capable of generating robust protective immunity and contains some functional neutralizing epitopes. In the present study, we produced and characterized a recombinant L-HN fusion fragment of the parent BoNT/B (BL-HN) composed of L and HN domains with a deletion in the Hc domain (BHc). When the BL-HN protein was expressed in E. coli, it retained its stable structure and antigenicity. As a vaccine antigen, the recombinant BL-HN protein was found to induce sufficient protection against native BoNT/B in a mouse model. The BL-HN subunit vaccine could also induce a strong humoral immune response and generate sufficient neutralizing antibodies in immunized mice. Therefore, BL-HN may retain the native neurotoxin structure and critical epitopes responsible for inducing serum neutralizing antibodies. Studies of the dose-dependent immunoprotective effects further confirmed that the BL-HN antigen could provide potent protective immunity. This finding suggests that BL-HN can play an important role in immune protection against BoNT/B. Therefore, the BL-HN fusion fragment provides an excellent platform for the design of recombinant botulinum vaccines and neutralizing antibodies.
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Affiliation(s)
- Zhen Li
- Beijing Institute of Biotechnology, Beijing, 100071, China.,Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing, 100044, China
| | - Jian-Sheng Lu
- Beijing Institute of Biotechnology, Beijing, 100071, China
| | - Shan Liu
- PLA Rocket Force Characteristic Medical Center, Beijing, 100088, China
| | - Rong Wang
- Beijing Institute of Biotechnology, Beijing, 100071, China
| | - Qing Xu
- Institute of Life Science and Biotechnology, Beijing Jiaotong University, Beijing, 100044, China
| | - Yun-Zhou Yu
- Beijing Institute of Biotechnology, Beijing, 100071, China.
| | - Zhi-Xin Yang
- Beijing Institute of Biotechnology, Beijing, 100071, China.
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Rasetti-Escargueil C, Popoff MR. Antibodies and Vaccines against Botulinum Toxins: Available Measures and Novel Approaches. Toxins (Basel) 2019; 11:toxins11090528. [PMID: 31547338 PMCID: PMC6783819 DOI: 10.3390/toxins11090528] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 08/29/2019] [Accepted: 09/05/2019] [Indexed: 12/18/2022] Open
Abstract
Botulinum neurotoxin (BoNT) is produced by the anaerobic, Gram-positive bacterium Clostridium botulinum. As one of the most poisonous toxins known and a potential bioterrosism agent, BoNT is characterized by a complex mode of action comprising: internalization, translocation and proteolytic cleavage of a substrate, which inhibits synaptic exocytotic transmitter release at neuro-muscular nerve endings leading to peripheral neuroparalysis of the skeletal and autonomic nervous systems. There are seven major serologically distinct toxinotypes (A-G) of BoNT which act on different substrates. Human botulism is generally caused by BoNT/A, B and E. Due to its extreme lethality and potential use as biological weapon, botulism remains a global public health concern. Vaccination against BoNT, although an effective strategy, remains undesirable due to the growing expectation around therapeutic use of BoNTs in various pathological conditions. This review focuses on the current approaches for botulism control by immunotherapy, highlighting the future challenges while the molecular underpinnings among subtypes variants and BoNT sequences found in non-clostridial species remain to be elucidated.
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Affiliation(s)
- Christine Rasetti-Escargueil
- Institut Pasteur, Département de Microbiologie, Unité des Toxines Bactériennes, 25 Rue du Docteur Roux, 75015 Paris, France.
| | - Michel R Popoff
- Institut Pasteur, Département de Microbiologie, Unité des Toxines Bactériennes, 25 Rue du Docteur Roux, 75015 Paris, France.
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Wang YF, Liu F, Lan J, Bai J, Li XQ. The Effect of Botulinum Neurotoxin Serotype a Heavy Chain on the Growth Related Proteins and Neurite Outgrowth after Spinal Cord Injury in Rats. Toxins (Basel) 2018; 10:toxins10020066. [PMID: 29393906 PMCID: PMC5848167 DOI: 10.3390/toxins10020066] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Revised: 01/31/2018] [Accepted: 01/31/2018] [Indexed: 12/16/2022] Open
Abstract
(1) Background: The botulinum toxin A (BoNT-A) heavy chain (HC) can stimulate the growth of primary motor neurites. (2) Methods: A recombinant BoNT/A HC was injected locally plus interval intrathecal catheter of BoNT/A HC to rats with ipsilateral semi-dissociated lumbar spinal cord injuries (SCIs). First, 2D gel with a silver nitrate stain was applied to detect the general pattern of protein expression. Growth associated protein 43 (GAP-43) and superior cervical ganglion 10 (SCG10) were chosen to represent the altered proteins, based on their molecular weight and pI, and were used to further detect their expression. Meanwhile, the neuronal processes were measured. The measurements of thermal hyperalgesia and grasp power at the ipsilateral hindlimb were used to evaluate spinal sensory and motor function, respectively. (3) Results: The local injection of BoNT/A HC followed by its intrathecal catheter intervally altered the spinal protein expression pattern after an SCI; protein expression was similar to normal levels or displayed a remarkable increase. The changes in the expression and distribution of phosphorylated growth associated protein 43(p-GAP 43) and superior cervical ganglion 10 (SCG 10) indicated that the administration of BoNT/A HC to the SCI significantly amplified the expression of p-GAP43 and SCG10 (p < 0.05). Meanwhile, the positive immunofluorescent staining for both p-GAP43 and SCG10 was mainly present near the rostral aspect of the injury, both in the cytoplasm and the neuronal processes. Moreover, the outgrowth of neurites was stimulated by the BoNT/A HC treatment; this was evident from the increase in neurite length, number of branches and the percentage of cells with neuronal processes. The results from the spinal function tests suggested that the BoNT/A HC did not affect sensation, but had a large role in improving the ipsilateral hindlimb grasp power (p < 0.05). (4) Conclusions: The local injection with the intermittent intrathecal administration of BoNT/A heavy chain to rats with SCI increased the local expression of GAP-43 and SCG 10, which might be affiliated with the regeneration of neuronal processes surrounding the injury, and might also be favorable to the relief of spinal motor dysfunction.
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Affiliation(s)
- Ya-Fang Wang
- Department of Pathophysiology, Shanxi Medical University, Taiyuan 030001, China.
| | - Fu Liu
- Department of Pathophysiology, Shanxi Medical University, Taiyuan 030001, China.
| | - Jing Lan
- Department of Pathophysiology, Shanxi Medical University, Taiyuan 030001, China.
| | - Juan Bai
- Department of Pathophysiology, Shanxi Medical University, Taiyuan 030001, China.
| | - Xia-Qing Li
- Department of Pathophysiology, Shanxi Medical University, Taiyuan 030001, China.
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Protein Structure Facilitates High-Resolution Immunological Mapping. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2017; 24:CVI.00275-17. [PMID: 29046310 DOI: 10.1128/cvi.00275-17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Select agents (SA) pose unique challenges for licensing vaccines and therapies. In the case of toxin-mediated diseases, HHS assigns guidelines for SA use, oversees vaccine and therapy development, and approves animal models and approaches to identify mechanisms for toxin neutralization. In this commentary, we discuss next-generation vaccines and therapies against ricin toxin and botulinum toxin, which are regulated SA toxins that utilize structure-based approaches for countermeasures to guide rapid response to future biothreats.
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Ayyar BV, Atassi MZ. Effects of membrane properties on the binding activities of the H N and H C heavy-chain domains of botulinum neurotoxin A. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1864:1678-1685. [PMID: 27596061 DOI: 10.1016/j.bbapap.2016.09.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 08/15/2016] [Accepted: 09/01/2016] [Indexed: 10/21/2022]
Abstract
Binding behaviors of the HN and the HC domains of BoNT/A were investigated individually to identify if there exist any differences in their interaction with the cell membrane. Recombinant fragments corresponding to both BoNT/A HN and HC regions were prepared (HN519-845 and HC967-1296) and their binding to synaptic proteins was verified. The binding behaviors of these heavy-chain domains were analyzed by treating the Neuro 2a, a murine neuroblastoma cell line, with compounds known to alter membrane properties. Cholesterol depletion and lipid raft inhibition increased the binding of HN519-845 to Neuro 2a cells without affecting HC967-1296-cell interaction. Sphingolipid depletion decreased the binding of cells to both HC967-1296 and HN519-845 whereas, loading exogenous GD1a, on to the Neuro 2a cells, increased the binding of both the peptides to cells. Microtubule disruption of the Neuro 2a cells by nocodazole decreased the binding of both HC967-1296 and HN519-845 to the treated cells. Inhibition of the clathrin-mediated endocytosis using dynasore, chlorpromazine or potassium (K+) depletion buffer lowered the binding of both HC967-1296 and HN519-845 to the cells, but seemed to exert a more pronounced effect on the binding of HC967-1296 than on the binding of HN519-845. Results indicate that while both the HN and HC domains are involved in the binding of the toxin to neuronal cells there are differences in their behavior which probably stem from their respective amino acid composition and structural location in the toxin three-dimensional structure along with their intended role in translocation and internalization into the cells.
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Affiliation(s)
- B Vijayalakshmi Ayyar
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - M Zouhair Atassi
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA; Department of Pathology and Immunology, Baylor College of Medicine, Houston, TX 77030, USA.
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