Comparison of antigenicity of toxins produced by Clostridium botulinum type C and D strains

Analysis of epitope information related to Bacillus anthracis and Clostridium botulinum

We have reviewed the information about epitopes of immunological interest from Clostridium botulinum and Bacillus anthracis, by mining the Immune Epitope Database and Analysis Resource. For both pathogens, the vast majority of epitopes reported to date are derived from a single protein: the protective antigen of B. anthracis and the neurotoxin type A of C. botulinum. A detailed analysis of the data was performed to characterize the function, localization and conservancy of epitopes identified as neutralizing and/or protective. In order to broaden the scope of this analysis, we have also included data describing immune responses against defined fragments (over 50 amino acids long) of the relevant antigens. The scarce information on T-cell determinants and on epitopes from other antigens besides the toxins, highlights a gap in our knowledge and identifies areas for future research. Despite this, several distinct structures at the epitope and fragment level are described herein, which could be potential additions to future vaccines or targets of novel immunotherapeutics and diagnostic reagents.

Protection with recombinant Clostridium botulinum C1 and D binding domain subunit (Hc) vaccines against C and D neurotoxins

Recombinant botulinum Hc (rBoNT Hc) vaccines for serotypes C1 and D were produced in the yeast Pichia pastoris and used to determine protection against four distinct BoNT C and D toxin subtypes. Mice were vaccinated with rBoNT/C1 Hc, rBoNT/D Hc, or with a combination of both vaccines and challenged with BoNT C1, D, C/D, or D/C toxin. Mice receiving monovalent vaccinations were partially or completely protected against homologous toxin and not protected against heterologous toxin. Bivalent vaccine candidates completely survived challenges from all toxins except D/C toxin. These results indicate the recombinant C1 and D Hc vaccines are not only effective in a monovalent formula but offer complete protection against both parental and C/D mosaic toxin and partial protection against D/C mosaic toxin when delivered as a bivalent vaccine.

Effect of Nicking the C-terminal Region of the Clostridium botulinum Serotype D Neurotoxin Heavy Chain on its Toxicity and Molecular Properties

A unique strain of Clostridium botulinum serotype D 4947 produces toxin complexes that are composed of un-nicked components, including a neurotoxin (BoNT) and auxiliary proteins. This BoNT showed aberrant elution upon Superdex gel filtration, indicating a much lower molecular weight, due to hydrophobic interaction with the column. Limited trypsin proteolysis of BoNT produces two nicks; first nick yielded a BoNT 50 kDa light chain disulfide linked to a 100 kDa heavy chain (Hc), and a second nick arose in Hc C-terminal 10 kDa. The second nick occurred in the putative binding domain of the BoNT molecule and induced alterations in its secondary structure, leading to a significant reduction of mouse toxicity in comparison with that of the fully-activated singly nicked BoNT. These results help to clarify the role of the C-terminal half of the Hc in the oral toxicity of single-chain and more complex forms of BoNT.

Molecular composition of progenitor toxin produced by Clostridium botulinum type C strain 6813

The molecular composition of the purified progenitor toxin produced by a Clostridium botulinum type C strain 6813 (C-6813) was analyzed. The strain produced two types of progenitor toxins (M and L). Purified L toxin is formed by conjugation of the M toxin (composed of a neurotoxin and a non-toxic nonhemagglutinin) with additional hemagglutinin (HA) components. The dual cleavage sites at loop region of the dichain structure neurotoxin were identified between Arg444-Ser445 and Lys449-Thr450 by the analyses of C-terminal of the light chain and N-terminal of the heavy chain. Analysis of partial amino acid sequences of fragments generated by limited proteolysis of the neurotoxin has shown to that the neurotoxin protein produced by C-6813 was a hybrid molecule composed of type C and D neurotoxins as previously reported. HA components consist of a mixture of several subcomponents with molecular weights of 70-, 55-, 33-, 26 through 21- and 17-kDa. The N-terminal amino acid sequences of 70-, 55-, and 26 through 21-kDa proteins indicated that the 70-kDa protein was intact HA-70 gene product, and other 55- and 26 through 21-kDa proteins were derived from the 70-kDa protein by modification with proteolysis after translation of HA-70 gene. Furthermore, several amino acid differences were exhibited in the amino acid sequence as compared with the deduced sequence from the nucleotide sequence of the HA-70 gene which was common among type C (strains C-St and C-468) and D progenitor toxins (strains D-CB16 and D-1873).

Purification and characterization of ADP-ribosyltransferases (exoenzyme C3) of Clostridium botulinum type C and D strains

By cation-exchange column chromatography followed by gel filtration or hydroxylapatite column chromatography, ADP-ribosyltransferases (exoenzyme C3) were isolated from culture supernatants of Clostridium botulinum type C strains Stockholm (CST) and 6813 (C6813) and from type D strains South African (DSA) and 1873 (D1873), and their molecular properties were compared. The purified C3 enzymes were homogeneous in polyacrylamide gel electrophoresis. The C3 enzymes existed as single-chain polypeptides with molecular masses of 25.0 to 25.5 kDa and transferred ADP-riboses to the same substrates in rat brain membrane extract. The C3 enzymes could be roughly classified into two groups with respect to amino acid composition, amino-terminal sequence, and antigenicity. One group contains the C3 enzymes of strains C6813 and DSA, and the other contains those of strains CST and D1873. The specific activity of the C3 enzyme of strain C6813 was about 15 times higher than that of the C3 enzyme of strain CST. These results indicate that the classification of the C3 molecules differs from that of the neurotoxin molecules.

Detection of Clostridium botulinum types C and D toxin by ELISA

An ELISA to detect Clostridium botulinum type D toxin was developed using polyclonal antibodies to a semi-purified toxic complex of the neurotoxin. Sensitivity of the ELISA for detecting type C and type D toxin compared with mouse inoculation was 70% and specificity 96% on samples from animals with botulism diagnosed on clinical signs and herd history. However, both mouse inoculation and the ELISA failed to detect toxin in many animals with a presumptive diagnosis of botulism. Some cross-reaction was seen with Clostridium novyi type A, but not with other clostridial species. While the ELISA described here cannot replace mouse inoculation for the diagnosis of botulism, it is a useful additional test.

Molecular diversity of neurotoxins from Clostridium botulinum type D strains

The molecular properties of Clostridium botulinum type D South African (D-SA) were compared with those of neurotoxins from type D strain 1873 (D-1873) and type C strains Stockholm and 6813. D-SA toxin, purified 610-fold from the culture supernatant in an overall yield of 30%, consisted of an intact peptide chain with a molecular weight of 140,000. Limited proteolysis of the toxin by trypsin formed a dichain structure consisting of a light chain (Mr, 50,000) and a heavy chain (Mr, 90,000) linked by a disulfide bond(s) and enhanced the lethal activity about fourfold. Antibodies against the D-SA toxin light chain reacted with D-1873 toxin but not with C1 toxins. On the other hand, antibodies against the heavy chain of D-SA toxin cross-reacted with type C strain Stockholm, D-1873, and type C strain 6813 toxins in that order. Amino-terminal sequences of heavy and light chains of D-SA and D-1873 toxins were similar but not identical. These results indicate that within the type D strains, neurotoxins differ in molecular structure and antigenicity.

Clostridium botulinum type D neurotoxin: purification and detection

A method is reported for the purification of type D botulinum toxin using a combination of low and high pressure ion exchange chromatography. The procedure produced homogeneous toxin in its free form in 3 days, with a specific toxicity in mice of 5.4 x 10(7) LD50/mg protein. Polyclonal antibodies against the pure toxin were raised in rabbits and detected the toxin in both ELISA and western blotting. The antibodies also detected type C1 botulinum toxin using these techniques, confirming the presence of cross-reacting antigenic determinants in these two proteins.

Biochemical classification of Clostridium botulinum type C and D strains and their nontoxigenic derivatives

The biochemical properties of 11 toxigenic and 10 nontoxigenic type C and D strains of Clostridium botulinum were studied. All of the strains examined were motile and hemolytic and produced lipase and liquid gelatin. Fermentation of several sugars and the production of lecithinase, indole, and hydrogen sulfide varied with the strain. The strains were classified into four groups based on their sugar fermentation profiles. The resulting classification was identical to the classification which had been proposed from the relationship between toxin production and phages and similar to the grouping based on the nature of toxin antigenic structures. Lecithinase production was negative in the cells belonging to group III, and indole and hydrogen sulfide production was negative in the cells of groups III and IV. Strains belonging to groups III and IV have many characteristics different from those of groups I and II.

Purification and characterization of neurotoxin produced by Clostridium botulinum type C 6813

The toxin produced by Clostridium botulinum type C 6813 (C-6813) was purified 1,009-fold from the culture supernatant in an overall yield of 30%. The specific toxicity was 1.1 X 10(7) mouse minimum lethal doses per mg of protein. The toxin had a molecular weight of 144,000, composed of the light and heavy chains with molecular weights of 52,000 and 92,000, respectively, linked by one or two disulfide bond(s). The purified C-6813 toxin heavy and light chains reacted strongly with anti-type D heavy chain immunoglobulin G and anti-type C1 light chain immunoglobulin G, respectively. The amino acid compositions of C-6813 toxin heavy and light chains were more similar to those of type D heavy chain and type C1 light chain than to those of type C1 heavy chain and type D light chain, respectively. These results suggest that in the toxin produced by the type C strain at least two subtypes exist.