Inhibition of Cysteine and Serine Proteinases by the Cowpox Virus Serpin CRMA

Interleukin ls converting enzyme (ICE) is the founding member of a family of cysteine proteinases active in the metabolism of intracellular proteins [1]. Other members of this family include Ich-1, CPP32, Ced-3, all of which have been implicated in apoptosis (programmed cell death) [2–4]. Though ICE itself may also be involved in apoptosis, its main role is probably to activate pro-interleukin-ls (proIL-ls) via specific cleavage following Asp residues [1,5].