Lambda-toxin of Clostridium perfringens activates the precursor of epsilon-toxin by releasing its N- and C-terminal peptides

The effect of λ-toxin, a thermolysin-like metalloprotease of Clostridium perfringens, on the inactive ε-prototoxin produced by the same organism was examined. When the purified ε-prototoxin was incubated with the purified ε-toxin at 37 C for 2 hr, the 32.5-kDa ε-prototoxin was processed into a 30.5-kDa polypeptide, as determined by SDS-polyacrylamide gel electrophoresis. A mouse lethality test showed that the treatment activated the prototoxin: the 50% lethal doses (LD₅₀) of the prototoxin with and without λ-toxin treatment were 110 and 70,000 ng/kg of body weight, respectively. The lethal activity of the prototoxin activated by λ-toxin was comparable to that with trypsin plus chymotrypsin and higher than that with trypsin alone: LD₅₀ of the prototoxin treated with trypsin and trypsin plus chymotrypsin were 320 and 65 ng/kg of body weight, respectively. The ε- toxin gene was cloned and sequenced. Determination of the N-terminal amino acid sequence of each activated ε-prototoxin revealed that λ-toxin cleaved between the 10th and 11th amino acid residues from the N-terminus of the prototoxin, while trypsin and trypsin plus chymotrypsin cleaved between the 13th and 14th amino acid residues. The molecular weight of each activated ε- prototoxin was also determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The C-terminus deduced from the molecular weight is located at the 23rd or 30th amino acid residue from the C-terminus of the prototoxin, suggesting that removal of not only N-terminal but also C- terminal peptide is responsible for activation of the prototoxin.