It was cloned and sequenced light chain region of botulinum neurotoxin type B which is potent neurotoxin produced by Clostridium botulinum type B Lamanna. From amino acid sequences deduced from nucleic acid sequences, it was known that light chain of botulinum type B neurotoxin is composed of 441 codons and molecular mass is 58,827.5 Da. When the amino acid sequences of light chain was compared with that of other types of clostridial neurotoxin, BoNT/B has high similarity with BoNT/G and TeNT (61 % and 52 % similarity, respectively). These indicate that BoNT/B, BoNT/G and TeNT have a high genealogical relatedness.
Recombinant light chain was expressed and purified from E. coli with relatively simple chromatography using two ion exchange resin, DEAE-cellulose and phosphocellulose. The purified light chain actively cleaved the synaptobrevin of the mouse brain microsome. But when treated with metal chealating agent (EDTA or 2,2``-dipyridyl), the activity was inhibited. It was confirmed that the purified protein was light chain and was not contaminated with other protein with anti- recombinant light chain antibody obtained from rat. Native BoNT/B was also purified with APTG affinity chromatography which interacts with haemagglutinin moieties of neurotoxin complex and DEAE cellulose ion exchange chromatography.
When the activity of the recombinant light chain was compared with native BoNT/B in dose and time dependent manner, recombinant light chain have activity as same as that of native light chain. The activity of light chain was analyzed in various pH and salt concentration. The catalytic activity of the recombinant light chain was maintained stable from pH 3 to pH 9 but drastically decreased below pH 3.0 and above pH 9.0. The activity of light chain rapidly decreased in higher concentration than 0.2 M NaCl.