Botulinum neurotoxins (BoNTs) are among the most poisonous substances known to man, with a 50% lethal dose (LD50) of 1 ng/kg in mice. BoNTs therefore represent a major bioterrorist threat (Arnon et al., 2001; Gill, 1982). Paradoxically, BoNT-containing medicines and cosmetics, such as Botox(R), Dysport(R), Xeomin(R), CBTXA(R), Myobloc(R) and NeuroBloc(R), have been used with great success to treat a variety of neurological, otolaryngological, ophthalmological, urological, dermatological and gastrointestinal disorders (Jankovic, 2004; Truong and Jost, 2006). In October 2010, FDA approved Botox(R) to treat chronic migraine. Both the toxic and therapeutic functions of BoNTs rely on a common mechanism to enter neurons, cleave proteins that mediate exocytosis of key neurotransmitters, and subsequently paralyze the affected muscles. BoNTs are produced by Clostridium botulinum as large progenitor toxin complexes (PTCs) that include auxiliary clostridial proteins known as neurotoxin-associated proteins (NAPs) (Montecucco and Schiavo, 1995). Clinical formulations are also composed of BoNT PTCs. Accidental BoNT poisoning mainly occurs through oral ingestion of tainted food products. NAPs are thought to protect BoNTs against the hostile environment of the gastrointestinal (GI) tract, and to mediate toxin transport across the epithelial cell barriers, the first step of intoxication. However the underlying molecular mechanisms that control these processes are poorly understood. The goal of this proposal is to elucidate the structure and function of BoNT PTCs, including the mechanism by which NAPs protect BoNTs, the regulatory mechanism underlying PTC assembly, and the structural basis by which NAPs regulate the interaction between BoNTs and host cells. The focus of this proposal is on the serotype A of BoNT (BoNT/A), because it is a major concern for bioterrorism and is the most commonly used medicine among all BoNT serotypes. We will use a combination of techniques, including X-ray crystallography, together with biochemistry, biophysics, cell biology, toxicology and bioinformatics. If successful, the proposed wok will guide the design of novel therapeutics for the treatment and/or prevention of botulism. Our work may also provide new insights into the activity and side effects of drugs such as Botox(R) and Dysport(R), which may help improve their clinical efficacy and suggest novel clinical applications.

Public Health Relevance

Botulinum neurotoxins (BoNTs) are both deadly toxins and effective medicines. We propose to study the structure and function of BoNT progenitor toxin complexes, which are produced by the bacterium Clostridium botulinum and serve as sophisticated toxin protection and delivery machinery. The accomplishment of our goal will help to improve our defense against potential bioterrorist weapons, and will potentially improve the clinical applications of BoNTs.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Bacterial Pathogenesis Study Section (BACP)
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Ranallo, Ryan
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University of California Irvine
Schools of Medicine
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Lam, Kwok-Ho; Qi, Ruifeng; Liu, Shun et al. (2018) The hypothetical protein P47 of Clostridium botulinum E1 strain Beluga has a structural topology similar to bactericidal/permeability-increasing protein. Toxicon 147:19-26
Silva, Daniel-Adriano; Stewart, Lance; Lam, Kwok-Ho et al. (2018) Structures and disulfide cross-linking of de novo designed therapeutic mini-proteins. FEBS J 285:1783-1785
Chen, Peng; Tao, Liang; Wang, Tianyu et al. (2018) Structural basis for recognition of frizzled proteins by Clostridium difficile toxin B. Science 360:664-669
Yao, Guorui; Lam, Kwok-Ho; Weisemann, Jasmin et al. (2017) A camelid single-domain antibody neutralizes botulinum neurotoxin A by blocking host receptor binding. Sci Rep 7:7438
Chevalier, Aaron; Silva, Daniel-Adriano; Rocklin, Gabriel J et al. (2017) Massively parallel de novo protein design for targeted therapeutics. Nature 550:74-79
Yao, Guorui; Lam, Kwok-Ho; Perry, Kay et al. (2017) Crystal Structure of the Receptor-Binding Domain of Botulinum Neurotoxin Type HA, Also Known as Type FA or H. Toxins (Basel) 9:
Yao, Guorui; Zhang, Sicai; Mahrhold, Stefan et al. (2016) N-linked glycosylation of SV2 is required for binding and uptake of botulinum neurotoxin A. Nat Struct Mol Biol 23:656-62
Lam, Kwok-Ho; Jin, Rongsheng (2015) Architecture of the botulinum neurotoxin complex: a molecular machine for protection and delivery. Curr Opin Struct Biol 31:89-95
Lam, Tina I; Stanker, Larry H; Lee, Kwangkook et al. (2015) Translocation of botulinum neurotoxin serotype A and associated proteins across the intestinal epithelia. Cell Microbiol 17:1133-43
Lee, Kwangkook; Lam, Kwok-Ho; Kruel, Anna-Magdalena et al. (2015) Inhibiting oral intoxication of botulinum neurotoxin A complex by carbohydrate receptor mimics. Toxicon 107:43-9

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