Searching the databases of expressed sequence tags (est) for sequences related to caspase-3 and caspase-6 led to the cloning from Jurkat T cells of a novel cDNA encoding a 479-amino-acid protein named Mch4. Mch4 or caspase-10, which is more related to caspase-8 than to any other caspase. Like caspase-8, caspase-10 has an active-site QACQG pentapeptide and also contains two FADD-like DEDs (death effector domains) in its N-terminal domain, suggesting a possible role in CD95- or TNF- induced apoptosis. Mature caspase-10 is derived from a single-chain polypeptide proenzyme by cleavage at Asp-372 located between the large and small subunits.

Nothern blot analysis revealed that caspase-10 mRNA is present in most tissues, with lowest expression being observed in brain, kidney, prostate, testis and colon and higher levels in heart, liver and spleen. Recombinant caspase-10 is unusual in that it has similar K_m for the cleavage of both Ac-DEVD-AMC and Ac-YVAD-AMC, but is more similar to caspase-3 as it is potently inhibited by Ac-DEVD.CHO (Fernandes-Alnemri et al., 1996). Purified recombinant caspase-10 processes all caspases, including pro-caspases-3,-7 and -10 whereas neither caspase-3 nor caspase-7 cleaves pro-caspase-10, suggesting that the latter is upstream of both caspase-3 and caspase-7 and lies at or near the apex of a cascade of proteases (Fernandes-Alnemri et al., 1996; Srinivasula et al., 1996)