“…Until now, to our knowledge, no other substrate for IdeS had been identified (4,6). In addition, IdeS is not affected by the typical cysteine proteinase inhibitor E-64 (4,6), which is in sharp contrast to the described prokaryotic cysteine proteinases (16)(17)(18)(19), and suggests a unique catalytic property of IdeS. Like the classical streptococcal cysteine proteinase, SpeB (streptococcal pyrogenic exotoxin B), IdeS contains an RGD motif (4,14,15), which is involved in the interaction of IdeS with vitronectin (␣ V3 ) and platelet receptors (␣ II3 ) (21), suggesting additional, yet unknown properties of the enzyme.…”