Characterisation of botulinum toxins type C, D, E, and F by matrix-assisted laser desorption ionisation and electrospray mass spectrometry.

In a follow-up of the earlier characterisation of botulinum toxins type A and B (BTxA and BTxB) by mass spectrometry (MS), types C, D, E, and F (BTxC, BTxD, BTxE, BTxF) were now investigated. Botulinum toxins are extremely neurotoxic bacterial toxins, likely to be used as biological warfare agent. Biologically active BTxC, BTxD, BTxE, and BTxF are comprised of a protein complex of the respective neurotoxins with non-toxic non-haemagglutinin (NTNH) and, sometimes, specific haemagglutinins (HA). These protein complexes were observed in mass spectrometric identification. The BTxC complex, from Clostridium botulinum strain 003-9, consisted of a 'type C1 and D mosaic' toxin similar to that of type C strain 6813, a non-toxic non-hemagglutinating and a 33 kDa hemagglutinating (HA-33) component similar to those of strain C-Stockholm, and an exoenzyme C3 of which the sequence was in full agreement with the known genetic sequence of strain 003-9. The BTxD complex, from C. botulinum strain CB-16, consisted of a neurotoxin with the observed sequence identical with that of type D strain BVD/-3 and of an NTNH with the observed sequence identical with that of type C strain C-Yoichi. Remarkably, the observed protein sequence of CB-16 NTNH differed by one amino acid from the known gene sequence: L859 instead of F859. The BTxE complex, from a C. botulinum isolated from herring sprats, consisted of the neurotoxin with an observed sequence identical with that from strain NCTC 11219 and an NTNH similar to that from type E strain Mashike (1 amino acid difference with observed sequence). BTxF, from C. botulinum strain Langeland (NCTC 10281), consisted of the neurotoxin and an NTNH; observed sequences from both proteins were in agreement with the gene sequence known from strain Langeland. As with BTxA and BTxB, matrix-assisted laser desorption/ionisation (MALDI) MS provided provisional identification from trypsin digest peptide maps and liquid chromatography-electrospray (tandem) mass spectrometry (LC-ES MS) afforded unequivocal identification from amino acid sequence information of digest peptides obtained in trypsin digestion.

Characterisation of botulinum toxins type A and B, by matrix-assisted laser desorption ionisation and electrospray mass spectrometry.

A method earlier developed for the mass spectrometric (MS) identification of tetanus toxin (TTx) was applied to botulinum toxins type A and B (BTxA and BTxB). Botulinum toxins are extremely neurotoxic bacterial toxins, likely to be used as biological warfare agent. Biologically active BTxA and BTxB are comprised of a protein complex of the respective neurotoxins with specific haemagglutinins (HAs) and non-toxic non-haemagglutinins (NTNHs). These protein complexes are also observed in mass spectrometric identification. The particular BTxA complex, from Clostridium botulinum strain 62A, almost completely matched database data derived from genetic sequences known for this strain. Although no such database information was available for BTxB, from C. botulinum strain okra, all protein sequences from the complex except that of HA-70 were found to match proteins known from other type B strains. It was found that matrix-assisted laser desorption ionisation MS provides provisional identification from trypsin digest peptide maps and that liquid chromatography electrospray (tandem) mass spectrometry affords unequivocal identification from amino acid sequence information of digest peptides obtained in trypsin or pepsin digestion.

Characterization of tetanus toxin, neat and in culture supernatant, by electrospray mass spectrometry.

A method was developed for the liquid chromatographic-mass spectrometric (LC-MS) identification of extremely neurotoxic toxins. The method combines sample treatment in a safety containment and analysis of detoxified material in a common laboratory facility. The method was applied to the characterization of neat tetanus toxin and subsequent identification of the toxin in cell lysate supernatants and culture supernatants from different Clostridium tetani bacteria strains. Characterization of the neat toxin was accomplished by (1) accurate mass measurement of enzyme digest fragments of the toxin and (2) tandem mass spectrometric (MS/MS) amino acid sequencing of selected peptides. Accurate mass measurement proved no longer feasible for the analysis of supernatants, due to the overwhelming presence of peptides from proteins other than toxin. Even when high-molecular-weight proteins were filtered from the lysates and treated, the retained protein fraction yielded too many peptides. However, MS/MS could successfully be applied when the findings from the characterization of neat toxin were employed. Thus, LC-MS/MS of selected precursor ions from trypsin digest fragments yielded specific sequence data for identification of the toxin. This procedure provided reliable identification of the toxin at levels above 1 microg/ml and within a day. Investigations with the method developed will be extended to the botulinum neurotoxins.