THE PRIMARY STRUCTURE OF CLOSTRIDIUM-SEPTICUM ALPHA-TOXIN EXHIBITS SIMILARITY WITH THAT OF AEROMONAS-HYDROPHILA AEROLYSIN

The gene for Clostridium septicum alpha-toxin was cloned and expressed in Escherichia coli from C. septicum BX96. The toxin was determined t o be 443 amino acids in length, with a 31-residue signal peptide that was removed from the toxin during secretion. No extended hydrophobic r egions were observed in the mature toxin sequence, Expression of alpha -toxin in E. call BL21 resulted in the production of AT(pro), which wa s identical to native toxin from C. septicum with respect to activity and activation. The proteolytic activation site for alpha-toxin was de termined to be on the carboxy-terminal side of arginine 398, which lie s within the sequence KKRRGKR-398SVD. Previous work showing similariti es in activation and mechanism between alpha-toxin and Aeromonas hydro phila aerolysin was extended to the primary structures of both toxins. The DNA-derived primary sequence of alpha-toxin exhibited 27% identit y and 72% similarity over a 387-residue region with the primary struct ure of the A. hydrophila aerolysin toxin, a level of similarity hereto fore unobserved between toxins produced by a gram-positive organism an d a gram-negative organism.