Cysteine proteases calpains

E-64 is an epoxide-containing natural product identified as a potent nonselective, calpain inhibitor, with demonstrated efficacy in animal models of AD. Several E-64 derivatives have been developed [542], Hyperactivation of the calcium-dependent cysteine protease calpain 1 (Call) is implicated as a primary or secondary pathological event in a wide range of illnesses and in neurodegen-erative states, including AD. 

Yamashima T. Implication of cysteine proteases calpain, cathepsin and caspase in ischemic neuronal death of primates. Prog Neurobiol. 2000 62 273-295... 

In higher organisms, calpain superfamily contains 16 independent genes that modulate cellular function. Out of them, 14 are Ca2+-dependent cysteine proteases. The other two encode smaller regulatory proteins that... 

Domain II is composed of two subdomains (Ha and lib) and represents the catalytic core of the protease. A cys at position 115 (p,-calpain) or 105 (m-calpain), a His residue at position 272 ((x-calpain) or 262 (m-calpain) and an Asn residue at position 296 ( x-calpain) or 286 (m-calpain) form the catalytic triad characteristic of cysteine proteases such as papain or cathepsins B, L, or S. Domain II, however, shares only limited sequence homology with other cysteine proteases, and is likely to have evolved from a different ancestral gene. 

A distinctive feature of calpain-3 is the propensity to autolysis the half life of the protein in vitro is less than 30 minutes. Autoproteolysis is prevented by replacing the cys residue of the catalytic site with a ser, but is not affected by cysteine protease inhibitors such as calpastatin, E64 and Leupeptin (Sorimachi et al., 1993). The autocatalytic activity and the absence of effective inhibitors have made the... 

Sustained cytosolic Ca2+ overload usually results in a different route leading to cell death. It mainly relies on the activation of the calcium/calmodulin (CaM)-dependent phosphatase, calcineurin. Calcineurin-catalyzed dephosphorylation promotes apoptosis by regulating the activity of a number of downstream targets, including the pro-apoptotic Bcl-2 family member, Bad (Wang, et al., 1999), and transcription factors of the NFAT (nuclear factor of activated T cells) family (Rao, et al., 1997). There are also other Ca2+-dependent enzymes contributing to the apoptotic events, and they include several DNA-degrading endonucleases (Robertson, et al., 2000) and Ca2+-activated cystein proteases of the calpain family essential for the enzymatic activation of the crucial pro-apoptotic effectors (Altznauer, et al., 2004). 

Cysteine proteases are so called because of a critical cysteine involved (together with an adjacent histidine) in the catalytic mechanism. Cysteine proteases include papain-related proteases, calpain-related proteases and the caspases. Papain-like cysteine proteases include the plant enzymes actinidin, aleurain, bromelain, caricain, chymopapain, ficin and papain and the lysosomal cathepsins B, C, H, K, L and S. Cathepsin C is multimeric (MW -200,000), but the other papain-related proteases are monomeric with MWs of about 20,000-35,000. While cathepsin C is a dipeptidyl aminopeptidase, the other enzymes are endopeptidases. Cathepsin B is an endopeptidase and a dipeptidyl carboxypeptidase. Cathepsin H is an endopeptidase and an aminopeptidase. In higher animals, cathepsin B generates peptides from antigens for presentation to T cells by the major histocompatibility... 

Cysteine proteases, called calpains, are known to be activated by sustained elevations in intracellular free calcium. Once activated, calpains degrade the cytoskeleton, transmitter and membrane channels, and metabolic enzymes (Hou and MacManus 2002 Mattson 2003 Nicholls 2004). Functionally, calpains have been characterized as pivotal mediators of both active necrotic cell death and PCD (Wang 2000) following cell-damaging stressors and insults such as soman exposure, excitotoxic challenges, toxins, free radicals, UV radiation, acute hypoxia, traumatic brain injury, cytokines, heat, and in chronic neurodegenerative conditions (Fischer et al. 1991 Caner et al. 

Calpains are cytosolic Ca- -dependent cysteine proteases [45]. They are located close to the cytoskeleton and mostly degrade cytoskeletal proteins, protein kinases, phosphatases, membrane receptors, transport proteins, and regulatory proteins [46,47]. Stimulation of calpain activity was shown following oxidative stress [48-55] in combination with an increase in intracellular Ca concentration [50, 54]. No studies exist that point towards a selective recognition of oxidized protein substrates by calpains [56]. However, it has been demonstrated that the oxidized cytoskeletal protein ezrin is degraded by the proteasome [57]. 

Interestingly, the apoptotic activity of the nuclear assembly extracts had an absolute requirement for a subcellular fraction highly enriched in mitochondria. The system was used to test the effect of various treatments on apoptosis and it was found that the observed nuclear changes were inhibited by the addition of, amongst other things, inhibitors of calpain (a cysteine protease see Section 7). 

Calpains Calcium-dependent cysteine proteases Many different cellular roles... 

Calpains are a family of calcium-dependent cysteine proteases that are widely expressed in brain and spinal cord tissues. These enzymes have been implicated in cell death in spinal cord injury (Ray et al., 2003 Buki et al., 2003). Calpain activity is modulated by an endogenous protein inhibitor called calpastatin. Overactivation... 

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