Nucleotide sequence of the gene for perfringolysin O (theta-toxin) from Clostridium perfringens: significant homology with the genes for streptolysin O and pneumolysin

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Abstract
The nucleotide sequence was determined for the gene encoding the thiol-activated cytolysin, perfringolysin O (theta-toxin), from Clostridium perfringens. The nucleotide-sequence-derived primary structure of perfringolysin O is 499 residues long and exhibits a 27-amino-acid signal peptide. The calculated molecular weight of the secreted (mature) form of perfringolysin O is 52,469. The deduced amino-terminal sequence of perfringolysin O is identical to that determined for purified perfringolysin O. Hydropathy analysis indicated that, except for the signal peptide, no major stretches of hydrophobic residues are present. Extensive amino acid sequence homology (65%) was detected with the low-molecular-weight form of streptolysin O, and a lesser amount (42%) was detected with pneumolysin. The nucleotide sequence of the perfringolysin O gene (pfo) exhibits approximately 60% homology with the streptolysin O gene (slo) and 48% homology with the pneumolysin gene (ply). All three toxins contain an identical region of 12 amino acids, which includes the essential cysteine of all three toxins. The location of these 12 residues was conserved in all three toxins when the primary sequences were aligned for maximum homology.