`Bacterial Disease Mechanisms by Wilson, McNab and Henderson (2002) states that thiol-activated cytolysin is now known to be an incorrect description, as:  ``this term 'thiol-activated' is now known to be incorrectly applied to this family of toxins and stemmed from initial studies suggesting that the single conserved cysteine residue of each toxin was essential for cytotoxicity. Site-directed mutagenesis of this cysteine residue, which resides in an 11 amino acid residue C-terminal-located sequence conserved across the family, has demonstrated that the cysteine residue is not required for activity. In fact, changing cysteine to alanine in pneumonlysin (produced by Strep. pneumoniae) does not affect cytotoxicity, channel formation or complement activation.``  Debunking the initial studies: ``Neither crude extracts of the cysteine-to-alanine mutant version of pneumolysin nor highly purified toxin require thiol activation and it is now thought that contaminants in early preparations were responsible for oxidative loss of activity of pneumolysin and other cholesterol-binding toxins.   New putative mechanisms: ``However, other mutations within the conserved 11-amino acid residue sequence can abolish cytotoxicity and it is now believed that the secondary structure of this region is important for cytotoxicity```