Fast protein liquid chromatography of botulinum neurotoxin types A, B and E

Holotoxin Activity of Botulinum Neurotoxin Subtype A4 Originating from a Nontoxigenic Clostridium botulinum Expression System

Clostridium botulinum subtype A4 neurotoxin (BoNT/A4) is naturally expressed in the dual-toxin-producing C. botulinum strain 657Ba at 100× lower titers than BoNT/B. In this study, we describe purification of recombinant BoNT/A4 (rBoNT/A4) expressed in a nonsporulating and nontoxigenic C. botulinum expression host strain. The rBoNT/A4 copurified with nontoxic toxin complex components provided in trans by the expression host and was proteolytically cleaved to the active dichain form. Activity of the recombinant BoNT/A4 in mice and in human neuronal cells was about 1,000-fold lower than that of BoNT/A1, and the recombinant BoNT/A4 was effectively neutralized by botulism heptavalent antitoxin. A previous report using recombinant truncated BoNT/A4 light chain (LC) expressed in Escherichia coli has indicated reduced stability and activity of BoNT/A4 LC compared to BoNT/A1 LC, which was surmounted by introduction of a single-amino-acid substitution, I264R. In order to determine whether this mutation would also affect the holotoxin activity of BoNT/A4, a recombinant full-length BoNT/A4 carrying this mutation as well as a second mutation predicted to increase solubility (L260F) was produced in the clostridial expression system. Comparative analyses of the in vitro, cellular, and in vivo activities of rBoNT/A4 and rBoNT/A4-L260F I264R showed 1,000-fold-lower activity than BoNT/A1 in both the mutated and nonmutated BoNT/A4. This indicates that these mutations do not alter the activity of BoNT/A4 holotoxin. In summary, a recombinant BoNT from a dual-toxin-producing strain was expressed and purified in an endogenous clostridial expression system, allowing analysis of this toxin.

Monoclonal antibody-based enzyme immunoassay for detection of botulinum neurotoxin type A

A sensitive and specific ELISA was developed to detect BoNT/A in biological fluids. The assay is based on the sandwich format using monoclonal antibodies (MAb) of two distinct specificities. An affinity-purified anti-BoNT/A heavy chain MAb (150-3) is utilized to adsorb BoNT/A from solution; the second anti-BoNT/A heavy chain MAb (44-1A) conjugated with peroxidase is then used to form a sandwich. Peroxidase allows color development and measurement of optical density at 450 nm. Standard curves were linear over the range of 2.5 to 100 ng/mL BoNT/A. The limit of detection was below 5 ng/mL in assay buffer, as well as in a 1:10 dilution of urine or 1:50 dilution of human serum spiked with BoNT/A. The developed BoNT/A assay also showed no cross-reaction to type B neurotoxin (BoNT/B) and type E neurotoxin (BoNT/E).

Detection of Botulinum Neurotoxin A in a Spiked Milk Sample with Subtype Identification through Toxin Proteomics

Botulinum neurotoxin (BoNT) causes the disease botulism, which can be lethal if untreated. Rapid determination of exposure to BoNT is an important public health goal. Previous work in our laboratory focused on the development of Endopep-MS, a mass spectrometry-based endopeptidase method for detecting and differentiating BoNT in buffer. This method can rapidly determine the presence of BoNT in a sample and differentiate the toxin type of BoNT present but does not yield additional information about the subtype. We now describe here the application of Endopep-MS to detect BoNT A in a spiked milk sample. This work also describes subtype identification achieved through mass spectrometric analysis of the protein toxin itself and does not require the presence of DNA from the toxin-producing bacteria. Tryptic digests of A1 and A2 subtypes of BoNT were analyzed by mass spectrometry, and peptides unique to either the A1 or A2 subtype were subjected to tandem mass spectrometry analysis to confirm their identities. Finally, subtype identification through mass spectrometric analysis was performed on BoNT A isolated from spiked milk. In its entirety, this method would allow for analysis of BoNT with toxin type identification in a few hours and subtype identification within 24 h.

Colloidal gold-based immunochromatographic assay for detection of botulinum neurotoxin type B

A rapid immunochromatographic assay was developed to detect botulinum neurotoxin type B (BoNT/B). The assay was based on the sandwich format using polyclonal antibody (Pab). The thiophilic gel purified anti-BoNT/B Pab was immobilized to a defined detection zone on a porous nitrocellulose membrane and conjugated to colloidal gold particles that served as a detection reagent. The BoNT/B-containing sample was added to the membrane and allowed to react with Pab-coated particles. The mixture was then passed along the porous membrane by capillary action past the Pab in the detection zone, which will bind the particles that had BoNT/B bound to their surface, giving a red colour within this detection zone with an intensity proportional to BoNT/B concentration. In the absence of BoNT/B, no immunogold was bound to the solid-phase antibody. With this method, 50 ng/ml of BoNT/B was detected in less than 10 min. The assay sensitivity can be increased by silver enhancement to 50 pg/ml. The developed BoNT/B assay also showed no cross reaction to type A neurotoxin (BoNT/A) and type E neurotoxin (BoNT/E).

Botulinum neurotoxin types B and E: purification, limited proteolysis by endoproteinase Glu-C and pepsin, and comparison of their identified cleaved sites relative to the three-dimensional structure of type A neurotoxin

Botulinum neurotoxin (NT) serotypes B and E are approximately 150 kDa proteins. Isolated from the liquid culture of Clostridium botulinum the NT type E is a single chain protein while the NT type B, from the proteolytic strain of the bacteria, is a mixture of dichain (nicked within a disulfide loop located about one-third the way from the N-terminus to the C-terminus) protein and its precursor single-chain protein. Endoproteinase Glu-C (EC 3.4.21.19) and pepsin (EC 3.4.23.1) were used for controlled digestion of NT types B and E; the amino acid residues flanking many of the cleavable peptide bonds were identified and the corresponding proteolytic fragments partially characterized. Chemical identification of 82 and 108 residues of types B and E NT, respectively, revealed that the residue 738 and 1098 in type E NT, identified as Leu and Asn, respectively, differ from those deduced from nucleotide sequences. Several fragments overlapped spanning various segments of the NT's functional domains; they appear to have potential for structure-function studies of the NT. The cleavage sites were compared with the previously determined proteolyzed sites on NT types A and E. The cleavage sites of the NT types A, B and E, all exposed on the protein surface, were scrutinized in the context of the three-dimensional structure of crystallized NT type A [Lacy, D.B., Stevens, R.C., 1999. J. Mol. Biol. 291, 1091-1104]. Detailed procedures for isolation of pure NT types B and E in large quantities (average yield 92 and 62 mg, respectively) suitable for crystallization are reported.

Botulinum toxin type A inhibits Ca(2+)-dependent transport of acetylcholine in reconstituted giant liposomes made from presynaptic membranes from cholinergic nerve terminals

Giant liposomes were made from a mixture of asolectin phospholipid vesicles and presynaptic plasma membranes isolated from Torpedo cholinergic nerve endings. Acetylcholine filled giant liposomes were able to release neurotransmitter upon stimulation by the Ca2+ ionophore A23187 and Ca2+. Botulinum neurotoxin type A inhibited this Ca(2+)-dependent acetylcholine transport. Additionally, Botulinum toxin type A decreased membrane fluidity of liposomes. These results suggest that Botulinum toxin can interact directly with components of the presynaptic plasma membrane and inhibit acetylcholine translocation. Furthermore, since the reconstituted liposomes do not have synaptic vesicle components, the observed effects may account for the action of Botulinum toxin on the non-quantal release of acetylcholine from motor nerve terminals.