Protease responsible for the cleavage of IcsA between 'Arg-758' and 'Arg-759', removing the entire alpha domain from IscA localized on the bacterial surface. This proteolytic activity contributes to the maintenance of a tight polar cap of IcsA, which is important to Shigella actin-based motility. Transcriptionally regulated by VirB (InvE). Belongs to the peptidase A26 family.