The caspase family represents a new class of intracellular cysteine proteases with known or suspected roles in cytokine maturation and apoptosis. These enzymes display a preference for Asp in the P1 position of substrates. To clarify differences in the biological roles of the interleukin-1␤ converting enzyme (ICE) family proteases, we have examined in detail the specificities beyond the P1 position of caspase-1, -2, -3, -4, -6, and -7 toward minimal length peptide substrates in vitro. We find differences and similarities between the enzymes that suggest a functional subgrouping of the family different from that based on overall sequence alignment. The primary specificities of ICE homologs explain many observed enzyme preferences for macromolecular substrates and can be used to support predictions of their natural function(s). The results also suggest the design of optimal peptidic substrates and inhibitors.A growing body of evidence supports important roles for the interleukin-1␤ converting enzyme (ICE) 1 (1, 2) and its homologs (recently renamed caspases (3)) in cytokine maturation and apoptosis. The caspase gene family, defined by protein sequence homology but also characterized by conservation of key catalytic and substrate-recognition amino acids, includes caspase-2 (4), caspase-3 (5-7), caspase-4 (8 -10), caspase-5 (10), caspase-6 (11), caspase-7 (12-14), caspase-8 (15-17), caspase-9 (18, 19), and caspase-10 (17). Each is an intracellular cysteine protease that shares with the serine protease granzyme B specificity for Asp in the P1 position of substrates. The specific biological roles and interrelationships of these enzymes are for the most part unknown and are areas of active investigation in many laboratories.A role for caspase-1 in inflammation is supported by several lines of evidence. Caspase-1-deficient mice, and cells derived from those animals, are deficient in IL-1␤ maturation and are resistant to endotoxic shock (20,21). Peptidic inhibitors of caspase-1 can be effective in blocking maturation and release of IL-1␤ by cultured cells (1) and in whole animals (22, 23) and of inflammation in animal models (24,25). The selectivity of the inhibitors employed in these studies among the caspases has not been demonstrated, and so the precise role of each caspase in inflammation is uncertain. Nevertheless the results uphold the promise of caspase-1 and/or its homologs as targets for anti-inflammatory drug discovery.Caspases play important roles in apoptosis signaling and effector mechanisms. Sequence alignments reveal homology with Ced-3 (26), a nematode cysteine protease (27, 28) that is required for cell death. The viral proteins CrmA and p35 are antiapoptotic and act by inhibition of caspases (29,30). A bacterial invasin induces apoptosis by binding to and activating caspase-1 specifically (31). Caspase-3 is necessary and sufficient for apoptosis in one acellular model (6); however, in mice the essential function of this enzyme is limited to apoptosis in the brain (32). A hallmark of apoptosis is the pr...

Recent studies have shown that protein kinase C (PKC) δ is proteolytically activated at the onset of apoptosis induced by DNA-damaging agents, tumor necrosis factor, and anti-Fas antibody. However, the relationship of PKCδ cleavage to induction of apoptosis is unknown. The present studies demonstrate that full-length PKCδ is cleaved at DMQD330N to a catalytically active fragment by the cysteine protease CPP32. The results also demonstrate that overexpression of the catalytic kinase fragment in cells is associated with chromatin condensation, nuclear fragmentation, induction of sub-G1 phase DNA and lethality. By contrast, overexpression of full-length PKCδ or a kinase inactive PKCδ fragment had no detectable effect. The findings suggest that proteolytic activation of PKCδ by a CPP32-like protease contributes to phenotypic changes associated with apoptosis.

Native human platelet factor 4 (PF4) is a homotetrameric protein (70 residues/subunit) known for its anticoagulant heparin binding activity. 2D 15N--1H HSQC NMR experiments of native PF4 in solution show the presence of conformational heterogeneity consistent with the formation of asymmetric homo-tetramers as observed in the X-ray crystal structure of both human and bovine PF4. A chimeric mutant of PF4 (called PF4-M2) which substitutes the first 11 N-terminal residues for the first eight residues from homologous interleukin-8 forms symmetric homo-tetramers with essentially the same heparin binding activity as native PF4. The solution structure of PF4-M2 has been investigated by using two- and three-dimensional 1H- and 15N-NMR spectroscopy and NOE-restrained simulated annealing molecular dynamics. As with other members of the CXC chemokine family whose structures are known, the PF4-M2 subunit monomer consists of a mostly hydrophobic, triple-stranded antiparallel beta-sheet onto which is folded an amphipathic C-terminal helix and a less periodic N-terminal domain. Although N-terminal substitution with the less acidic interleukin-8 sequence most affects the quarternary structure relative to native PF4 at the AC and AD dimer interfaces, AB dimer stability is weakened as reflected in reduced equilibrium association binding constants.

These results indicate the restorative materials to be potentially toxic, particularly if the degree of light-cure is inadequate.