Enhancement of the Endopeptidase Activity of Purified Botulinum Neurotoxins A and E by an Isolated Component of the Native Neurotoxin Associated Proteins

Bacterial AB toxins and host-microbe interactions

AB toxins are protein virulence factors secreted by many bacterial pathogens, contributing to the pathogenicity of the cognate bacteria. AB toxins consist of two functionally distinct components: the enzymatic "A" component for pathogenicity and the receptor-binding "B" component for toxin delivery. Consistently, unlike other virulence factors such as effectors, AB toxins do not require additional systems to deliver them to the target host cells. Target host cells are located in the infection site and/or located distantly from infected host cells. The first part of this review discusses the structural and functional features of single-peptide and multiprotein AB toxins in the context of host-microbe interactions, using several well-characterized examples. The second part of this review discusses toxin neutralization strategies, as well as applications of AB toxins relevant to developing intervention strategies against diseases.

Bioinformatics analysis and experimental validation of differentially expressed genes in mouse articular chondrocytes treated with IL-1β using microarray data

Osteoarthritis (OA) is the most prevalent chronic degenerative disease that affects the health of the elderly. The present study aimed to identify significant genes involved in OA via bioinformatics analysis. A gene expression dataset (GSE104793) was downloaded from the Gene Expression Omnibus. Bioinformatics analysis was then performed in order to identify differentially expressed genes (DEGs) between untreated chondrocytes and chondrocytes cultured with interleukin-1β (IL-1β) for 24 h. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using Metascape. A protein-protein interaction network of DEGs was constructed using the Search Tool for the Retrieval of Interacting Genes. Gene set enrichment analysis (GSEA) was performed using GSEA software. Furthermore, chondrocytes were extracted and treated with IL-1β (10 ng/ml) for 24 h, and reverse-transcription quantitative PCR was used to confirm differential expression of hub genes. Patient samples were also collected to verify the bioinformatic analysis results. Based on the cut-off criteria used for determination of the DEGs, a total of 844 DEGs, including 498 upregulated and 346 downregulated DEGs, were identified. The DEGs were mainly enriched in the GO terms and KEGG pathways 'inflammatory response', 'negative regulation of cell proliferation', 'ossification', 'taxis', 'blood vessel morphogenesis', 'extracellular structure organization', 'mitotic cell cycle process' and 'TNF signaling pathway'. The majority of the PCR results, namely the differential expression of kininogen 2, complement C3, cyclin B1, cell division cycle 20, cyclin A2, 1-phosphatidylinositol 4-kinase, BUB1 mitotic checkpoint serine/threonine kinase, kinesin family member 11, cyclin B2 and BUB1 mitotic checkpoint serine/threonine kinase B were consistent with the bioinformatics results. Collectively, the present observations provided a regulation network of IL-1β-stimulated chondrocytes, which may provide potential targets of OA therapy.

Clostridial Neurotoxins: Structure, Function and Implications to Other Bacterial Toxins

Gram-positive bacteria are ancient organisms. Many bacteria, including Gram-positive bacteria, produce toxins to manipulate the host, leading to various diseases. While the targets of Gram-positive bacterial toxins are diverse, many of those toxins use a similar mechanism to invade host cells and exert their functions. Clostridial neurotoxins produced by Clostridial tetani and Clostridial botulinum provide a classical example to illustrate the structure-function relationship of bacterial toxins. Here, we critically review the recent progress of the structure-function relationship of clostridial neurotoxins, including the diversity of the clostridial neurotoxins, the mode of actions, and the flexible structures required for the activation of toxins. The mechanism clostridial neurotoxins use for triggering their activity is shared with many other Gram-positive bacterial toxins, especially molten globule-type structures. This review also summarizes the implications of the molten globule-type flexible structures to other Gram-positive bacterial toxins. Understanding these highly dynamic flexible structures in solution and their role in the function of bacterial toxins not only fills in the missing link of the high-resolution structures from X-ray crystallography but also provides vital information for better designing antidotes against those toxins.

The mechanisms of action and use of botulinum neurotoxin type A in aesthetics: Key Clinical Postulates II

BACKGROUND

The literature on botulinum neurotoxin type A (BoNT-A) is extensive, often contradictory, and confounded by a competitive market of products and research attempting to distinguish brand individuality.

METHODS

A comprehensive review of literature on the principles of BoNT-A in aesthetics as well as clinical examples.

RESULTS

In 2017, the Eight Key Clinical Postulates were formulated as a guide for the aesthetic practitioner in understanding BoNT-A pharmacodynamics and to compare different toxins. These are now updated to include (a) All type A toxins act identically; (b) The mathematical relationship between toxin and receptor is the basis of efficacy, and clinical efficacy is influenced by molecular potency and patient attributes including muscle mass, gender, age, and ethnicity; (c) Efficacy, onset, and duration are functions of "molecular potency" defined as the number of active 150 kDa molecules available for binding; (d) "Molecular potency" is difficult to objectively quantify for commercially available toxins; (e) Up to a point, increased molecular potency decreases time to onset and increases duration of effect, and the "Molecular Potency Quotient" is a construct for comparing molecular potency commercial cost; (f) The area of effect of a toxin injection is dependent upon molecular potency, diffusion (passive), and spread (active); (g) Differing reconstitution volumes; and (h) Increased number of injection sites can affect spread, onset, and duration of effect.

CONCLUSIONS

The principles of BoNT-A use in aesthetics are complex yet understandable as outlined in the framework of the updated Eight Key Clinical Postulates and serves as a useful tool for providing the most effective treatment and interpreting research on present and future toxin formulations.

Role of critical elements in botulinum neurotoxin complex in toxin routing across intestinal and bronchial barriers

The highly potent botulinum neurotoxin serotype A (BoNT/A) inhibits neurotransmitter release at neuromuscular junctions resulting in flaccid muscle paralysis, respiratory arrest and death. In order to reach their neuronal cell targets, BoNT/A must cross epithelial cell barriers lining the intestines and airways. The toxin is produced as a large protein complex comprised of the neurotoxin and non-toxic neurotoxin-associated proteins (NAPs). Although NAPs are known to protect the toxin from harsh environments, their role in the movement of BoNT/A across epithelial barriers has not been fully characterized. In the current study, movement of the toxin across epithelial cells was examined macroscopically using a sensitive near infrared fluorescence transcytosis assay and microscopically using fluorescently labeled toxin and confocal microscopy. The studies show that the BoNT/A complex internalizes more rapidly than the pure toxin. The studies also show that one NAP protein, hemaglutinin 33 (Hn33), enhanced both the binding and movement of a deactivated recombinant botulinum neurotoxin A (DrBoNT) across epithelial cell monolayers and that the toxin associates with Hn33 on the cell surface. Collectively, the data demonstrate that, in addition to their protective role, NAPs and Hn33 play an important role in BoNT/A intoxication.

Differential endopeptidase activity of different forms of type A botulinum neurotoxin: A unique relationship between the size of the substrate and activity of the enzyme

Botulinum neurotoxins (BoNTs; serotypes A-G) are metalloproteases, which cleave and inactivate cellular proteins essential for neurotransmitter release. In bacterial cultures, BoNTs are secreted as a complex of the neurotoxin and a group of neurotoxin associated proteins (NAPs). Under physiological condition (pH 7.4), this complex is believed to be dissociated to separate the neurotoxin from NAPs. BoNT consists of a 50 kDa light (L) chain (LC or catalytic domain) and a 100 kDa heavy (H) chain (or HC) linked through a disulfide bond and other non-covalent interactions. The cell intoxication involves three major steps; binding, membrane translocation and inhibition of neurotransmitter release. The last step of intoxication, endopeptidase activity, is very unique and specific that can be used for detection of the complex and isolated forms of the toxin. A fluorescent tag-labeled synthetic peptide (SNAPtide) derived from a segment of SNAP-25, an intracellular substrate of BoNT/A, is used to detect and assay the endopeptidase activity of BoNT/A. The detection of the signal is based on the change in the fluorescence energy transfer after selective cleavage of the peptide by the BoNT/A. In this report, we demonstrate that SNAPtide as a commonly used substrate widely differ in reaction with BoNT/A complex, BoNT/A, and BoNT/A light chain. These findings have implications for assays used in detection, and in screening potential inhibitors.

Building-block architecture of botulinum toxin complex: Conformational changes provide insights into the hemagglutination ability of the complex

Clostridium botulinum produces the botulinum neurotoxin (BoNT). Previously, we provided evidence for the “building-block” model of botulinum toxin complex (TC). In this model, a single BoNT is associated with a single nontoxic nonhemagglutinin (NTNHA), yielding M-TC; three HA-70 molecules are attached and form M-TC/HA-70, and one to three “arms” of the HA-33/HA-17 trimer (two HA-33 and one HA-17) further bind to M-TC/HA-70 via HA-17 and HA-70 binding, yielding one-, two-, and three-arm L-TC. Of all TCs, only the three-arm L-TC caused hemagglutination. In this study, we determined the solution structures for the botulinum TCs using small-angle X-ray scattering (SAXS). The mature three-arm L-TC exhibited the shape of a “bird spreading its wings”, in contrast to the model having three “arms”, as revealed by transmission electron microscopy. SAXS images indicated that one of the three arms of the HA-33/HA-17 trimer bound to both HA-70 and BoNT. Taken together, these findings regarding the conformational changes in the building-block architecture of TC may explain why only three-arm L-TC exhibited hemagglutination.

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We examined the structures of botulinum TCs using SAXS.

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The mature three-arm L-TC exhibited the shape of a “bird spreading its wings”.

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One of the three arms of the HA-33/HA-17 trimer bound to both HA-70 and BoNT.

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The building-block architecture may explain hemagglutination by the three-arm L-TC.

"Non-Toxic" Proteins of the Botulinum Toxin Complex Exert In-vivo Toxicity

The botulinum neurotoxin (BoNT) causes muscle paralysis and is the most potent toxin in nature. BoNT is associated with a complex of auxiliary “Non-Toxic” proteins, which constitute a large-sized toxin complex (L-TC). However, here we report that the “Non-Toxic” complex of serotype D botulinum L-TC, when administered to rats, exerts in-vivo toxicity on small-intestinal villi. Moreover, Serotype C and D of the “Non-Toxic” complex, but not BoNT, induced vacuole-formation in a rat intestinal epithelial cell line (IEC-6), resulting in cell death. Our results suggest that the vacuole was formed in a manner distinct from the mechanism by which Helicobacter pylori vacuolating toxin (VacA) and Vibrio cholerae haemolysin induce vacuolation. We therefore hypothesise that the serotype C and D botulinum toxin complex is a functional hybrid of the neurotoxin and vacuolating toxin (VT) which arose from horizontal gene transfer from an ancestral BoNT-producing bacterium to a hypothetical VT-producing bacterium.

Cleavage of SNAP25 and its shorter versions by the protease domain of serotype A botulinum neurotoxin

Various substrates, catalysts, and assay methods are currently used to screen inhibitors for their effect on the proteolytic activity of botulinum neurotoxin. As a result, significant variation exists in the reported results. Recently, we found that one source of variation was the use of various catalysts, and have therefore evaluated its three forms. In this paper, we characterize three substrates under near uniform reaction conditions using the most active catalytic form of the toxin. Bovine serum albumin at varying optimum concentrations stimulated enzymatic activity with all three substrates. Sodium chloride had a stimulating effect on the full length synaptosomal-associated protein of 25 kDa (SNAP25) and its 66-mer substrates but had an inhibitory effect on the 17-mer substrate. We found that under optimum conditions, full length SNAP25 was a better substrate than its shorter 66-mer or 17-mer forms both in terms of kcat, Km, and catalytic efficiency kcat/Km. Assay times greater than 15 min introduced large variations and significantly reduced the catalytic efficiency. In addition to characterizing the three substrates, our results identify potential sources of variations in previous published results, and underscore the importance of using well-defined reaction components and assay conditions.

Expression and purification of neurotoxin-associated protein HA-33/A from Clostridium botulinum and evaluation of its antigenicity

BACKGROUND

Botulinum neurotoxin (BoNT) complexes consist of neurotoxin and neurotoxin-associated proteins. Hemagglutinin-33 (HA-33) is a member of BoNT type A (BoNT/A) complex. Considering the protective role of HA-33 in preservation of BoNT/A in gastrointestinal harsh conditions and also its adjuvant role, recombinant production of this protein is favorable. Thus in this study, HA-33 was expressed and purified, and subsequently its antigenicity in mice was studied.

METHODS

Initially, ha-33 gene sequence of Clostridium botulinum serotype A was adopted from GenBank. The gene sequence was optimized and synthesized in pET28a (+) vector. E. coli BL21 (DE3) strain was transformed by the recombinant vector and the expression of HA-33 was optimized at 37°C and 5 h induction time.

RESULTS

The recombinant protein was purified by nickel nitrilotriacetic acid agarose affinity chromatography and confirmed by immunoblotting. Enzyme Linked Immunoassay showed a high titer antibody production in mice.

CONCLUSION

The results indicated a highly expressed and purified recombinant protein, which is able to evoke high antibody titers in mice.

Purification and characterization of neurotoxin complex from a dual toxin gene containing Clostridium Botulinum Strain PS-5

Botulinum neurotoxins are produced as a toxin complex (TC) which consists of neurotoxin (NT) and neurotoxin associated proteins. The characterization of NT in its native state is an essential step for developing diagnostics and therapeutic countermeasures against botulism. The presence of NT genes was validated by PCR amplification of toxin specific fragments from genomic DNA of Clostridium botulinum strain PS-5 which indicated the presence of both serotype A and B genes on PS-5 genome. Further, TC was purified and characterized by Western blotting, Digoxin-enzyme linked immunosorbent assay, endopeptidase activity assay, and Liquid chromatography-Mass spectrometry. The data showed the presence of serotype A specific neurotoxin. Based on the analysis of neurotoxin genes and characterization of TC, PS-5 strain appears as a serotype A (B) strain of C. botulinum which produces only serotype A specific TC in the cell culture medium.

Development of a fluorescence internal quenching correction factor to correct botulinum neurotoxin type A endopeptidase kinetics using SNAPtide

Botulinum neurotoxins (BoNTs), which are highly toxic proteins responsible for botulism, are produced by different strains of Clostridium botulinum. These various strains of bacteria produce seven distinct serotypes, labeled A-G. Once inside cells, the zinc-dependent proteolytic light chain (LC) degrades specific proteins involved in acetylcholine release at neuromuscular junctions causing flaccid paralysis, specifically synaptosomal-associated protein 25 (SNAP-25) for botulinum neurotoxin type A (BoNT/A). BoNT endopeptidase assays using short substrate homologues have been widely used and developed because of their ease of synthesis, detection limits, and cost. SNAPtide, a 13-amino acid fluorescence resonance energy transfer (FRET) peptide, was used in this study as a SNAP-25 homologue for the endopeptidase kinetics study of BoNT/A LC. SNAPtide uses a fluorescein isothiocyanate/4-((4-(dimethylamino)phenyl)azo) benzoic acid (FITC/DABCYL) FRET pair to produce a signal upon substrate cleavage. Signal quenching can become an issue after cleavage since quencher molecules can quench cleaved fluorophore molecules in close proximity, reducing the apparent signal. This reduction in apparent signal provides an inherent error as SNAPtide concentrations are increased. In this study, fluorescence internal quenching (FIQ) correction factors were derived using an unquenched SNAPtide peptide to quantify the signal quenching over a range of SNAPtide concentrations and temperatures. The BoNT/A LC endopeptidase kinetics at the optimally active temperature (37 °C) using SNAPtide were studied and used to demonstrate the FIQ correction factors in this study. The FIQ correction factors developed provide a convenient method to allow for improved accuracy in determining and comparing BoNT/A LC activity and kinetics using SNAPtide over a broad range of concentrations and temperatures.

Microarray analysis of differentially regulated genes in human neuronal and epithelial cell lines upon exposure to type A botulinum neurotoxin

Among the seven serotypes (A-G), type A botulinum neurotoxin (BoNT/A) is the most prevalent etiologic agent and the most potent serotype to cause foodborne botulism, characterized by flaccid muscle paralysis. Upon ingestion, BoNT/A crosses epithelial cell barriers to reach lymphatic and circulatory systems and blocks acetylcholine release at the pre-synaptic cholinergic nerve terminals of neuromuscular junctions (NMJs) resulting in paralysis. One of the unique features of BoNT/A intoxication is its neuroparalytic longevity due to its persistent catalytic activity. The persistent presence of the toxin inside the cell can induce host cell responses. To understand the pathophysiology and host response at the cellular level, gene expression changes upon exposure of human HT-29 colon carcinoma (epithelial) and SH-SY5Y neuroblastoma cell lines to BoNT/A complex were investigated using microarray analysis. In HT-29 cells, 167 genes were up-regulated while 60 genes were down-regulated, whereas in SH-SY5Y cells about 223 genes were up-regulated and 18 genes were down-regulated. Modulation of genes and pathways involved in neuroinflammatory, ubiquitin-proteasome degradation, phosphatidylinositol, calcium signaling in SH-SY5Y cells, and genes relevant to focal adhesion, cell adhesion molecules, adherens and gap junction related pathways in HT-29 cells suggest a massive host response to BoNT/A. A clear differential response in epithelial and neuronal cells indicates that the genes affected may play a distinct role in BoNTs cellular mode of action, involving these two types of host cells.

Studies on the dissociation of botulinum neurotoxin type A complexes

The neurotoxins produced by the various strains of the anaerobic bacterium Clostridium botulinum naturally occur associated with complexing proteins which serve to protect the neurotoxins from the harsh environment of the mammalian gastrointestinal tract during bacterial invasion of the host. Three different complex species with the discrete sizes 19S (900 kDa, LL complex), 16S (500 kDa, L complex) and 12S (300 kDa, M complex) may be isolated from C. botulinum type A cultures. However, to affect their target cells these complexes must dissociate releasing the free 150 kDa neurotoxin. This study assesses the stability of these Clostridium botulinum neurotoxin serotype A (BoNT/A) complexes and identifies factors which influence their dissociation. The knowledge gained with purified toxin complexes was subsequently employed to analyze the presence of such complexes in the freeze or spray-dried commercial BoNT/A products Botox and Dysport in comparison to the complexing protein free product Xeomin. Purified 900 kDa and 500 kDa toxin complex preparations show a pH and time dependent release of the 150 kDa neurotoxin with a half-life of less than a minute at pH values >7.0. At pH values of 6.25 or less, the complexes are stable. Furthermore, dilution of concentrated 900 kDa complexes leads to dissociation into 500 kDa, neurotoxin containing complexes. Addition of sodium chloride as contained in isotonic saline leads to further disruption of these complexes resulting in the release of the free 150 kDa neurotoxin. Examination of the commercial botulinum neurotoxin products Botox and Dysport using the same analytical procedures leads to the same conclusion: the dilution, drying and reconstitution processes of these products lead to a complete dissociation of 900 kDa complexes and 85% or more of neurotoxin are present in free form.

CONCLUSION

BoNT A toxin complexes have evolved to quickly respond to specific environmental changes by efficient release of the neurotoxin. During pharmaceutical production and reconstitution of BoNT A products, the same principles effect the quantitative dissociation of 900 kDa complexes and release of free neurotoxin prior to injection into target tissues.

Endopeptidase activities of botulinum neurotoxin type B complex, holotoxin, and light chain

Botulinum neurotoxin (BoNT) serotype B (BoNT/B) is one of the serotypes of BoNT that causes deadly human botulism, though it is used clinically for treatment of many neuromuscular diseases. BoNT/B is produced by Clostridium botulinum, and it is secreted along with a group of neurotoxin-associated proteins (NAPs) in the form of a BoNT/B complex. The complex dissociates into a 150-kDa holotoxin and NAPs at alkaline pHs. The 150-kDa BoNT/B holotoxin can be nicked to produce a 50-kDa domain referred to as the light chain (LC) and a 100-kDa heavy chain, with the former possessing a unique endopeptidase activity. The two chains remain linked through a disulfide bond that can be reduced to separate the two chains. The endopeptidase activity is present in all three forms of the toxin (complex, purified BoNT/B holotoxin, and separated light chain), which are used by different researchers to develop detection methods and screen for inhibitors. In this research, the endopeptidase activities of the three forms, for the first time, were compared under the same conditions. The results show that enzyme activities of the three forms differ significantly and are largely dependent on nicking and disulfide reduction conditions. Under the conditions used, LC had the highest level of activity, and the complex had the lowest. The activity was enhanced by nicking of BoNT/B holotoxin and was enhanced even more by dithiothreitol (DTT) reduction after nicking. This information is useful for understanding the properties of BoNT endopeptidases and for comparing the efficacies of different inhibitors when they are tested with different forms of BoNT endopeptidase.

Molecular basis of activation of endopeptidase activity of botulinum neurotoxin type E

Botulinum neurotoxins (BoNTs) are a group of large proteins that are responsible for the clinical syndrome of botulism. The seven immunologically distinct serotypes of BoNTs (A-G), each produced by various strains of Clostridium botulinum, act on the neuromuscular junction by blocking the release of the neurotransmitter acetylcholine, thereby resulting in flaccid muscle paralysis. BoNTs are synthesized as single inactive polypeptide chains that are cleaved by endogenous or exogenous proteases to generate the active dichain form of the toxin. Nicking of the single chain BoNT/E to the dichain form is associated with 100-fold increase in toxicity. Here we investigated the activation mechanism of botulinum neurotoxin type E upon nicking and subsequent reduction of disulfide bond. It was observed that nicking of BoNT/E significantly enhances its endopeptidase activity and that at the physiological temperature of 37 degrees C the reduced form of nicked BoNT/E adopts a dynamically flexible conformation resulting from the exposure of hydrophobic segments and facilitating optimal cleavage of its substrate SNAP-25. Such reduction-induced increase in the flexibility of the polypeptide folding provides a rationale for the mechanism of BoNT/E endopeptidase against its intracellular substrate, SNAP-25, and complements current understanding of the mechanistics of interaction between the substrate and BoNT endopeptidase.

Interaction of botulinum toxin with the epithelial barrier

Botulinum neurotoxin (BoNT) is a protein toxin (approximately 150 kDa), which possesses a metalloprotease activity. Food-borne botulism is manifested when BoNT is absorbed from the digestive tract to the blood stream and enters the peripheral nerves, where the toxin cleaves core proteins of the neuroexocytosis apparatus and elicits the inhibition of neurotransmitter release. The initial obstacle to orally ingested BoNT entering the body is the epithelial barrier of the digestive tract. Recent cell biology and molecular biology studies are beginning to elucidate the mechanism by which this large protein toxin crosses the epithelial barrier. In this review, we provide an overview of the structural features of botulinum toxins (BoNT and BoNT complex) and the interaction of these toxins with the epithelial barrier.

The identification and biochemical characterization of drug-like compounds that inhibit botulinum neurotoxin serotype A endopeptidase activity

A robust, high-throughput, two-tiered assay for screening small molecule inhibitors against botulinum neurotoxin serotype A was developed and employed to screen 16,544 compounds. Thirty-four compounds were identified as potent hits employing the first-tier assay. Subsequently, nine were confirmed as actives by our second-tier confirmatory assay. Of these, one displayed potent inhibitory efficacy, possessing an IC(50)=16 microM (+/-1.6 microM) in our in vitro assay. This inhibitor (0831-1035) is highly water-soluble, and possesses an IC(50)=47 microM (+/-7.0 microM) in our primary cell culture assay (with virtually no cytotoxicity up to 500 microM), suggesting that this inhibitor is a good candidate for further development as a therapeutic countermeasure to treat botulism resulting from botulinum neurotoxin serotype A intoxication. An enzyme kinetics study indicated that this inhibitor exhibits mixed non-competitive inhibition, with a K(I)=9 microM.

Immunological characterization of the subunits of type A botulinum neurotoxin and different components of its associated proteins

Botulinum neurotoxins (BoNTs) constitute a family of seven structurally similar but antigenically distinct proteins produced by different strains of Clostridium botulinum. Type A botulinum neurotoxin (BoNT/A) is produced along with 6 neurotoxin associated proteins (NAPs) including hemagglutinin (Hn-33) through polycistronic expression of a clustered group of genes to form a complex (BoNT/AC). The presence of NAPs enhances the oral toxicity of the neurotoxin significantly. Hn-33 makes up the largest fraction of NAPs in BoNT/AC and strongly protects BoNT/A against proteases of the GI tract. BoNT in its complex form is also used in therapeutic and cosmetic applications to treat several neuromuscular disorders. In this study immunological reactivity of BoNT/A in its purified and complex forms, neurotoxin associated proteins, and Hn-33 have been examined using enzyme-linked immunosorbent assay (ELISA). Antibodies raised against the whole complex reacted 60 times better with the complex and 35 times better with Hn-33 and NAPs compared to the purified neurotoxin suggesting stronger immunogenicity of NAPs over that of purified neurotoxin and a higher potential of BoNT/AC and its associated proteins to induce host immune response. This observation also suggests that Hn-33 and other NAPs could potentially be employed as adjuvants for development of vaccines against botulism and could be a good surrogate for botulinum diagnostics. ELISA binding curves of BoNT/AC and BoNT/A with antibodies raised against BoNT/A indicate that BoNT/A in its purified and complex forms induces equal immunogenic response and a 2.5-fold higher immunogenic response compared to BoNT/A light and heavy chains. We have also discovered a new protein, an intimin analog, present within the complex preparation of BoNT/A which shows dramatically high immunoreactivity.

Dysport: pharmacological properties and factors that influence toxin action

The pharmacological properties of Dysport that influence toxin action are reviewed and compared with other botulinum toxin products. In particular, the subject of diffusion is examined and discussed based upon the evidence that currently exists, both from laboratory studies and from clinical data. Diffusion of botulinum toxin products is not related to the size of the toxin complex in the product since the complex dissociates under physiological conditions, releasing the naked neurotoxin to act. The active neurotoxin in Type A products is the same and therefore diffusion is equal when equal doses are administered.

Thermostable llama single domain antibodies for detection of botulinum A neurotoxin complex

Immunoglobulins from animals of the Camelidae family boast unique forms that do not incorporate light chains. Antigen binding in these unconventional heavy-chain homodimers is mediated through a single variable domain. When expressed recombinantly these variable domains are termed single domain antibodies (sdAb) and are among the smallest naturally IgG-derived antigen binding units. SdAb possess good solubility, thermostability, and can refold after heat and chemical denaturation making them promising alternative recognition elements. We have constructed a library of phage-displayed sdAb from a llama immunized with a cocktail of botulinum neurotoxin (BoNT) complex toxoids and panned the library for binders for BoNT A complex toxoid. Six unique binders were isolated and found to specifically bind BoNT A complex in toxoid and untoxoided forms and when used in optimal combinations in buffer and milk could detect 100 pg/mL untoxoided complex. All sdAb retained their ability to specifically bind target after heating to 85 degrees C for 1 h, in contrast to conventional polyclonal sera. All of the sdAb were highly specific for subtype A1 rather than A2 and demonstrated binding to the 33 kDa hemagglutinin, potentially to a somewhat overlapping linear epitope. The unique properties of these sdAb may provide advantages for many diagnostic applications where long-term storage and in-line monitoring require very rugged yet highly specific recognition elements.

Development of improved SNAP25 endopeptidase immuno-assays for botulinum type A and E toxins

Botulinum neurotoxins contain proteases that cleave specific intra-neural proteins essential for neurotransmitter release. Toxin types A, E and C1 intra-cellularly cleave SNAP25 resulting in a flaccid paralysis. As a consequence, various different endopeptidase assays have been developed to specifically detect the toxins enzymatic activity, however, many of these suffer from variability, low sensitivity or unwanted interference exerted by product specific excipients. The current studies utilised solid phase synthesized SNAP25(137-206) peptide substrate, and specific antibody to either the SNAP25(190-197) or (173-180) octapeptide epitopes that become exposed following cleavage by toxin types A or E respectively. Assay sensitivity was increased 50 fold by the use of an optimal 0.5% Tween 20 concentration in tandem to 0.1% albumin together with an improved, simplified assay design without a pre-activation / reduction step. Sensitivities capable of detecting 0.01 LD50/ml (40fg/ml or 0.3fM) of type A toxin was achieved with a linear dose response between 0.1 and 1 LD50/ml. This provides sufficient sensitivity and precision (inter assay GCV of < 2%) for monitoring activity within any current or newly marketed therapeutic products containing less units per vial and may also make it applicable for other applications. Both purified haemagglutinin free and complexed toxins could be detected equally. Unlike type A, type E activity could unexpectedly be detected in the complete absence of reducing conditions and the optimal assay had a limit of detection of 0.2LD50/ml (4.8pg/ml) with a linear dose response between 1 and 10LD50/ml. The principle of using a detecting antibody to a substrate sequence buried within the native substrates alpha-helix may be further expanded to other specific enzyme cleavage reactions in the future.

Stability of the Clostridium botulinum type A neurotoxin complex: an empirical phase diagram based approach

Clostridium botulinum type A neurotoxin (BoNT/A complex) is of great interest to the pharmaceutical industry. The drug itself is a natural complex of the toxin and a number of associated proteins. Surprisingly, relatively little is known about the exact structure and stability of the 900 kDa BoNT/A complex and its component proteins with the exception of the 150 kDa neurotoxin. In this study we describe the relative stability of the BoNT/A complex, the neurotoxin, and its associated proteins over a wide range of temperature and pH employing circular dichroism, intrinsic and 8-anilino-1-naphthalene sulfonate (ANS) fluorescence, and static light scattering. The data suggest a strong stabilizing effect of the associated proteins on the neurotoxin component. This data is compiled into empirical phase diagrams which permit the simultaneous visualization of multiple data sets over a wide range of conditions.

Cloning, Expression, Purification, and Characterization of Biologically Active Recombinant Hemagglutinin-33, Type A Botulinum Neurotoxin Associated Protein

Botulinum neurotoxin type A, the most toxic substance known to mankind, is produced by Clostridiurn botulinum type A as a complex with a group of neurotoxin-associated proteins (NAPs) through polycistronic expression of a clustered group of genes. Hemagglutinin-33 (Hn-33) is a 33 kDa subcomponent of NAPs, which is resistant to protease digestion, a feature likely to be involved in the protection of the botulinum neurotoxin from proteolysis. In order to fully understand the function of Hn-33, large amounts of Hn-33 will be needed without dealing with biosafety risks to grow large cultures of C. botulinum. There are difficulties to clone the genes with the high A + T contents produced by C. botulinum. We report here for the first time using the Gateway technology to clone functional Hn-33 that has been expressed in E. coli. The yield of the recombinant Hn-33 was about 12 mg per liter of E. coli culture. The recombinant Hn-33 folds well in aqueous solution as shown with circular dichroism spectra, resists temperature-denaturation, is totally resistant to trypsin proteolysis despite the presence of cleavage sites on the molecular surface, and maintains its biological activities comparable to the native Hn-33 hemagglutination.

Transport of bacterial toxins into target cells: pathways followed by cholera toxin and botulinum progenitor toxin

A number of bacterial toxins have sophisticated mechanisms for reaching their specific targets in mammalian cells, to exert their toxicity. This review focuses on the transport mechanisms of cholera toxin and botulinum neurotoxin complex. Cholera toxin is an ADP-ribosyltransferase toxin, and the covalent modification of heterotrimeric Gs protein in the cytosol leads to the activation of adenylyl cyclase and a sequence of events culminating in massive diarrheal disease. Here, we describe the structural features of this toxin and the transport pathway followed by this toxin from the plasma membrane to the cytosol of intestinal epithelial cells. Botulinum neurotoxin is a metalloprotease toxin that enters neurons, where it cleaves core proteins of the neuroexocytosis apparatus and elicits the inhibition of neurotransmitter release. The food-borne botulism is manifested when the neurotoxin is absorbed from the digestive tract, enters the blood stream, and reaches the cytosol of the peripheral nerves. We overview the structural organization and the long journey followed by this toxin.

Comparison of extracellular and intracellular potency of botulinum neurotoxins

Levels of botulinum neurotoxin (BoNT) proteolytic activity were compared using a cell-free assay and living neurons to measure extracellular and intracellular enzymatic activity. Within the cell-free reaction model, BoNT serotypes A and E (BoNT/A and BoNT/E, respectively) were reversibly inhibited by chelating Zn2+ with N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN). BoNT/E required relatively long incubation with TPEN to achieve total inhibition, whereas BoNT/A was inhibited immediately upon mixing. When naïve Zn2+-containing BoNTs were applied to cultured neurons, the cellular action of each BoNT was rapidly inhibited by subsequent addition of TPEN, which is membrane permeable. Excess Zn2+ added to the culture medium several hours after poisoning fully restored intracellular toxin activity. Unlike TPEN, EDTA irreversibly inhibited both BoNT/A and -E within the cell-free in vitro reaction. Excess Zn2+ did not reactivate the EDTA-treated toxins. However, application of EDTA-treated BoNT/A or -E to cultured neurons demonstrated normal toxin action in terms of both blocking neurotransmission and SNAP-25 proteolysis. Different concentrations of EDTA produced toxin preparations with incrementally reduced in vitro proteolytic activities, which, when applied to living neurons showed undiminished cellular potency. This suggests that EDTA renders the BoNT proteolytic domain conformationally inactive when tested with the cell-free reaction, but this change is corrected during entry into neurons. The effect of EDTA is unrelated to Zn2+ because TPEN could be applied to living cells before or after poisoning to produce rapid and reversible inhibition of both BoNTs. Therefore, bound Zn2+ is not required for toxin entry into neurons, and removal of Zn2+ from cytosolic BoNTs does not irreversibly alter toxin structure or function. We conclude that EDTA directly alters both BoNTs in a manner that is independent of Zn2+.

Botulinum neurotoxin structure, engineering, and novel cellular trafficking and targeting

Botulinum neurotoxins are multifaceted molecules, which are truly unique not only in their mode of action, but also their utility as a drug carrier either across the gut wall or to the nerve terminals. The molecule is divided in clear functional domains that can operate independently. This feature can be used to employ them as cargo carrier by linking other drugs or vaccines with the binding and translocation domains of BoNT. While the domain structures are largely independent of each other, the dynamic structure of these domains, especially that of the enzymatic domain (L chain), is quite different from the reported crystal structures for several BoNT serotypes and their enzymatic domain. This review discusses the comparative structures of BoNT in crystal and solution for their relevance to the molecular mechanism of BoNT action, especially in view of our recent discovery that the enzymatically active structure of the BoNT exists as a molten-globule and that of the endopeptidase domain as a novel PRIME conformation. Finally, a non-exhaustive discussion has been included to explain the long-lasting biological effects of certain serotypes of BoNT, based on the current knowledge of the structure-function of different serotypes of botulinum neurotoxins.

Methods for detection of Clostridium botulinum toxin in foods

Botulism is a deadly disease caused by ingestion of the preformed neurotoxin produced from the anaerobic spore-forming bacteria Clostridium botulinum. Botulinum neurotoxins are the most poisonous toxins known and have been a concern in the food industry for a long time. Therefore, rapid identification of botulinum neurotoxin using molecular and biochemical techniques is an essential component in the establishment of coordinated laboratory response systems and is the focus of current research and development. Because of the extreme toxicity of botulinum neurotoxin, some confirmatory testing with the mouse bioassay is still necessary, but rapid methods capable of screening large numbers of samples are also needed. This review is focused on the development of several detection methods for botulinum neurotoxins in foods.

Hemagglutinin-33 of type A botulinum neurotoxin complex binds with synaptotagmin II

Botulinum neurotoxin type A (BoNT/A), the most toxic substance known to mankind, is produced by Clostridium botulinum type A as a complex with a group of neurotoxin-associated proteins (NAPs) through polycistronic expression of a clustered group of genes. NAPs are known to protect BoNT against adverse environmental conditions and proteolytic digestion. Hemagglutinin-33 (Hn-33) is a 33 kDa subcomponent of NAPs that is resistant to protease digestion, a feature likely to be involved in the protection of the botulinum neurotoxin from proteolysis. However, it is not known whether Hn-33 plays any role other than the protection of BoNT. Using immunoaffinity column chromatography and pull-down assays, we have now discovered that Hn-33 binds to synaptotagmin II, the putative receptor of botulinum neurotoxin. This finding provides important information relevant to the design of novel anti-botulism therapeutic agents targeted to block the entry of botulinum neurotoxin into nerve cells.

Clostridium botulinum: a bug with beauty and weapon

Clostridium botulinum, a Gram-positive, anaerobic spore-forming bacteria, is distinguished by its significant clinical applications as well as its potential to be used as bioterror agent. Growing cells secrete botulinum neurotoxin (BoNT), the most poisonous of all known poisons. While BoNT is the causative agent of deadly neuroparalytic botulism, it also serves as a remarkably effective treatment for involuntary muscle disorders such as blepharospasm, strabismus, hemifacial spasm, certain types of spasticity in children, and other ailments. BoNT is also used in cosmetology for the treatment of glabellar lines, and is well-known as the active component of the anti-aging medications Botox and Dysport. In addition, recent reports show that botulinum neurotoxin can be used as a tool for pharmaceutical drug delivery. However, BoNT remains the deadliest of all toxins, and is viewed by biodefense researchers as a possible agent of bioterrorism (BT). Among seven serotypes, C. botulinum type A is responsible for the highest mortality rate in botulism, and thus has the greatest potential to act as biological weapon. Genome sequencing of C. botulinum type A Hall strain (ATCC 3502) is now complete, and has shown the genome size to be 3.89 Mb with a G+C content of approximately 28.2%. The bacterium harbors a 16.3 kb plasmid with a 26.8% G+C content--slightly lower than that of the chromosome. Most of the virulence factors in C. botulinum are chromosomally encoded; bioinformatic analysis of the genome sequence has shown that the plasmid does not harbor toxin genes or genes for related virulence factors. Interestingly, the plasmid does harbor genes essential to replication, including dnaE, which encodes the alpha subunit of DNA polymerase III which has close similarity with its counterpart in C. perfringens strain 13. The plasmid also contains similar genes to those that encode the ABC-type multidrug transport ATPase, and permease. The presence of ABC-type multidrug transport ATPase, and permease suggests putative involvement of efflux pumps in bacteriocin production, modification, and export in C. botulinum. The C. botulinum plasmid additionally harbors genes for LambdaBa04 prophage and site-specific recombinase that are similar to those found in the Ames strain of Bacillus anthracis; these genes and their products may play a role in genomic rearrangement. Completion of genome sequencing for C. botulinum will provide an opportunity to design genomic and proteomic-based systems for detecting different serotypes of C. botulinum strains in the environment. The completed sequence may also facilitate identification of potential virulence factors and drug targets, as well as help characterize neurotoxin-complexing proteins, their polycistronic expression, and phylogenetic relationships between different serotypes.