Purification and characterization of nontoxic protein complex from serotype D 4947 botulinum toxin complex

Construction of "Toxin Complex" in a Mutant Serotype C Strain of Clostridium botulinum Harboring a Defective Neurotoxin Gene

A non-toxigenic mutant of the toxigenic serotype C Clostridium botulinum strain Stockholm (C-St), C-N71, does not produce the botulinum neurotoxin (BoNT). However, the original strain C-St produces botulinum toxin complex, in which BoNT is associated with non-toxic non-hemagglutinin (NTNHA) and three hemagglutinin proteins (HA-70, HA-33, and HA-17). Therefore, in this study, we aimed to elucidate the effects of bont gene knockout on the formation of the "toxin complex." Nucleotide sequence analysis revealed that a premature stop codon was introduced in the bont gene, whereas other genes were not affected by this mutation. Moreover, we successfully purified the "toxin complex" produced by C-N71. The "toxin complex" was identified as a mixture of NTNHA/HA-70/HA-17/HA-33 complexes with intact NTNHA or C-terminally truncated NTNHA, without BoNT. These results indicated that knockout of the bont gene does not affect the formation of the "toxin complex." Since the botulinum toxin complex has been shown to play an important role in oral toxin transport in the human and animal body, a non-neurotoxic "toxin complex" of C-N71 may be valuable for the development of an oral drug delivery system.

Neurotoxins from Clostridium botulinum (serotype A) isolated from the soil of Mendoza (Argentina) differ from the A-Hall archetype and from that causing infant botulism

The type A of neurotoxin produced by Clostridium botulinum is the prevalent serotype in strains of Mendoza. The soil is the main reservoir for C.botulinum and is possibly one of the infection sources in infant botulism. In this study, we characterized and compared autochthonous C. botulinum strains and their neurotoxins. Bacterial samples were obtained from the soil and from fecal samples collected from children with infant botulism. We first observed differences in the appearance of the colonies between strains from each source and with the A Hall control strain. In addition, purified neurotoxins of both strains were found to be enriched in a band of 300 kDa, whereas the A-Hall strain was mainly made up of a band of ∼600 kDa. This finding is in line with the lack of hemagglutinating activity of the neurotoxins under study. Moreover, the proteolytic activity of C. botulinum neurotoxins was evaluated against SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins from rat brain. It was observed that both, SNAP 25 (synaptosomal-associated protein 25) and VAMP 2 (vesicle-associated membrane protein) were cleaved by the neurotoxins isolated from the soil strains, whereas the neurotoxins from infant botulism strains only induced a partial cleavage of VAMP 2. On the other hand, the neurotoxin from the A-Hall strain was able to cleave both proteins, though at a lesser extent. Our data indicate that the C.botulinum strain isolated from the soil, and its BoNT, exhibit different properties compared to the strain obtained from infant botulism patients, and from the A-Hall archetype.

Sugar-induced conformational change found in the HA-33/HA-17 trimer of the botulinum toxin complex

Large-sized botulinum toxin complex (L-TC) is formed by conjugation of neurotoxin, nontoxic nonhemagglutinin and hemagglutinin (HA) complex. The HA complex is formed by association of three HA-70 molecules and three HA-33/HA-17 trimers, comprised of a single HA-17 and two HA-33 proteins. The HA-33/HA-17 trimer isolated from serotype D L-TC has the ability to bind to and penetrate through the intestinal epithelial cell monolayer in a sialic acid-dependent manner, and thus it plays an important role in toxin delivery through the intestinal cell wall. In this study, we determined the solution structure of the HA-33/HA-17 trimer by using small-angle X-ray scattering (SAXS). The SAXS image of HA-33/HA-17 exhibited broadly similar appearance to the crystal image of the complex. On the other hand, in the presence of N-acetylneuraminic acid, glucose and galactose, the solution structure of the HA-33/HA-17 trimer was drastically altered compared to the structure in the absence of the sugars. Sugar-induced structural change of the HA-33/HA-17 trimer may contribute to cell binding and subsequent transport across the intestinal cell layer.