Preliminary evidence that different domains are involved in cytolytic activity and receptor (cholesterol) binding in listeriolysin O, theListeria monocytogenesthiol-activated toxin

The inactive truncated 52 Kilodaltons (kDa) Listeriolysin O (LLO) produced by a transposon Tn 1545-induced Listeria monocytogenes non-hemolytic/avirulent mutant previously described (Gaillard et al. (1986) Infect. Immun. 52, 55-55), that lacks a 48 aminoacid fragment at the C-terminal end including the single cysteine residue essential for activity (Mengaud et al. (1988) Infect. Immun. 56, 766–772), bound to the SH-cytolysin membrane receptor cholesterol, as did the active 60 kDa toxin. These results indicate that the missing fragment is a functionally important region needed in the 60 kDa LLo to cause membrane-disruption but not to bind to cholesterol, which strongly suggests that in LLO (and presumably in the other SH-cytolysins, in accordance with their structural and functional homologies) different domains are involved in cytolytic activity and cholesterol binding. The cysteine residue contained in the missing fragment, therefore, would not be essential for cholesterol binding, as in currently thought, rather it seems to be essential specifically for cell lysis.