THE ARCANOBACTERIUM (ACTINOMYCES) PYOGENES HEMOLYSIN, PYOLYSIN, IS A NOVEL MEMBER OF THE THIOL-ACTIVATED CYTOLYSIN FAMILY

Arcanobacterium (Actinomyces) pyogenes, an animal pathogen, produces a hemolytic exotoxin, pyolysin (PLO), The gene encoding PLO was cloned, and sequence analysis revealed an open reading frame of 1,605 bp enco ding a protein of 57.9 kDa. PLO has 30 to 40% identity with the thiol- activated cytolysins (TACYs) of a number of gram-positive bacteria, Th e activity of PLO was found to be very similar to allose of other TACY s, except that it was not thiol activated, The highly conserved TACY u ndecapeptide is divergent in PLO; in particular, the cysteine residue required for thiol activation has been replaced with alanine, However, mutagenesis of the alanine residue to cysteine did not confer thiol a ctivation on PLO, suggesting a conformational difference in thf undeca peptide region of this toxin, Specific antibodies against purified, re combinant PLO completely neutralized the hemolytic activity of A. pyog enes, suggesting that this organism produces a single hemolysin. Furth ermore, these antibodies could passively protect mice against lethal c hallenge with A, pyogenes, suggesting that like other TACYs PLO is an important virulence factor in the pathogenesis of this organism.