Preparation of specifically activatable endopeptidase derivatives of Clostridium botulinum toxins type A, B, and C and their applications

Clostridium botulinum neurotoxins are potently toxic proteins of 150 kDa with specific endopeptidase activity for SNARE proteins involved in vesicle docking and release. Following treatment with trypsin, a fragment of botulinum neurotoxin serotype A that lacks the C-terminal domain responsible for neuronal cell binding, but retains full catalytic activity, can be obtained. Known as the LH_N fragment, we report the development of a recombinant expression and purification scheme for the isolation of comparable fragments of neurotoxin serotypes B and C. Expressed as maltose-binding protein fusions, both have specific proteolytic sites present between the fusion tag and the light chain to facilitate removal of the fusion, and between the light chain endopeptidase and the H_N translocation domains to facilitate activation of the single polypeptide. We have also used this approach to prepare a new variant of LH _N/A with a specific activation site that avoids the need to use trypsin. All three LH_Ns are enzymatically active and are of low toxicity. The production of specifically activatable LH_N/A, LH _N/B, and LH_N/C extends the opportunities for exploitation of neurotoxin fragments. The potential utility of these fragments is discussed.