Small-molecule inhibitor: Ac-Ile-Glu-Thr-Asp-H

Name

History: Ac-Ile-Glu-Thr-Asp-H was designed by Han et al. (1997) to mimic the first natural autolytic cleavage site in caspase-3.
Peptidases inhibited: Although designed as an inhibitor of caspase-3, the compound is in fact a more potent inhibitor of several other caspases. Values for K_i (nM) (Salvesen & Nagase, 2001) are: < 6 (caspase-1), 9400 (caspase-2), 195 (caspase-3), 400 (caspase-4), 223 (caspase-5), 5.6 (caspase-6), 3280 (caspase-7), 1.05 (caspase-8), 108 (caspase-9).
Mechanism: Inhibition is reversible. A crystal structure of the complex with caspase-8 has been described (Watt et al., 1999).

Structure
Chemical/biochemical name: N-acetyl-isoleucyl-glutamyl-threonyl-aspartaldehyde
Related inhibitors: Boc-Ile-Glu-Thr-Asp-H

Inhibitor class: This is a compound of the aldehyde class. The discovery of leupeptin in the late 1960s drew attention to the potential of aldehydes as peptidase inhibitors, and the inhibition of papain by synthetic aldehydes was further studied by Wolfenden and co-workers (e.g. Westerik & Wolfenden, 1972). Many aldehydes are now known as inhibitors of serine, cysteine or threonine peptidases. They form hemiacetal or thiohemiacetal conjugates with the essential hydroxyl or thiol group of the enzyme that are transition state analogues (Bendall et al., 1977). The compounds exist predominantly in their hydrated forms in aqueous solution, but only the aldehyde is an effective inhibitor (Bendall et al., 1977). Peptide aldehydes and semicarbazones are valuable ligands for affinity chromatography of serine and cysteine peptidases (Rich et al., 1986; Dando & Barrett, 1992). Aldehydes can also act as inhibitors of metallopeptidases (Strater & Lipscomb, 1995).
Reviews: Garcia-Calvo et al. (1998)