Cholesterol-dependent cytolysins (CDC) are pore form-ing toxins. A prototype of the CDC family members is perfringolysin O (PFO), which directly binds to the cell membrane enriched in cholesterol, causing cell lysis.However, an exception of this general observation is intermedilysin (ILY) of Streptococcus intermedius, which requires human CD59 as a receptor in addition to cholesterol for its hemolytic activity. A possible explana-tion of this functional difference is the conformational variation between the C-terminal domains of the two toxins, particularly in the highly conserved undecapep-tide termed tryptophan rich motif. Here, we present the crystal structure of suilysin, a CDC toxin from the infectious swine pathogen Streptococcus suis. Like PFO, suilysin does not require a host receptor for hemolytic activity; yet the crystal structure of suilysin exhibits a similar conformation in the tryptophan rich motif to ILY. This observation suggests that the current view of the structure-function relationship between CDC proteins and membrane association is far from complete.