Suilysin (SLY)

Suilysin is a pore-forming cytolysin—a member of the cholesterol-dependent cytolysin (CDC) family—produced by the pathogenic bacterium *Streptococcus suis*. It acts as a major virulence factor by binding to cholesterol-containing membranes of host cells, oligomerizing to form large β-barrel pores that penetrate and lyse the cell membrane. Unlike some related CDCs (such as intermedilysin, which requires a specific cellular protein as co-receptor), suilysin does not require a protein receptor, binding directly to cholesterol to exert its cytolytic effect[1][3]. The structure and pore-forming mechanism involve a conformational transition from a soluble monomer to a large oligomeric pore complex, with substantial expansion and restructuring as the final pore forms in the host membrane[1][3]. Suilysin-mediated cytolysis contributes to the pathogenicity and immune evasion capabilities of *S. suis*, a significant pathogen in swine and an emerging zoonotic agent in humans[1][3]. Targeting suilysin or its pore-forming action is of interest for therapeutic intervention in streptococcal toxic shock and other severe infections, but no approved drugs currently exist that block its activity.

Other names

SLYStreptococcus suis cholesterol-dependent cytolysinStreptolysin S (only as a related family member, not a strict synonym)

Forms transmembrane pores via oligomerization on cholesterol-rich membranes, leading to cell membrane permeabilization and lysis