Cytolysin activated with thiols is capable of dissolving cholesterol-containing membranes. When the domain is reversibly inactivated, it is unable to bind to cholesterol. The Thiol_cytolys_C proteins contain a cysteine residue(100) at the C-terminus of cytolysin, required for cholesterol binding(101). Cholesterol is a necessary component of the membranes of red blood cells.But cholesterol may not be required for viral proteins to make their initial contact with red blood cells. We downloaded proteins involved in hemolysis from the UniProt database. We compared them to viral proteins to identify domains conserved in thiol-activated cytolysin (Table ).