Crystal structure of cytotoxin protein suilysin from Streptococcus suis

Abstract

Cholesterol-dependent cytolysins (CDC) are pore forming toxins. A prototype of the CDC family members is perfringolysin O (PFO), which directly binds to cholesterol rich cell membrane and lyses the cell. However, as an exception of this general observation, Streptococcus intermedius intermedilysin (ILY) requires human CD59 as its receptor in addition to cholesterol when exhibiting hemolytic activity. It was attempted to explain this functional difference based on a conformational variation in the C-terminal domain of the two toxin proteins, particularly a highly conserved undecapeptide termed tryptophan rich motif. Here, we present the crystal structure of suilysin, a CDC toxin from the swine infectious pathogen Streptococcus suis. Like PFO, suilysin does not require a host receptor for hemolytic activity; yet in the suilysin crystal it shares a similar conformation in the tryptophan rich motif with ILY. This observation suggests that current views of structure-function relationship of CDC proteins in membrane association are still far from complete.

Keywords

Suilysin / cholesterol-dependent cytolysin / crystal structure