M-Calpain

Alzheimer s disease Amount of m-calpain in the cytosolic but not the membranous fractions and in the neurofibrillary tangles of brain from Alzheimer s patients is increased37,38... 

Cataract formation Ca2+ influx activates m-calpain, the predominant calpain in lens, cleaving a- and 3- but not y-crystallins. The cry stall in fragments aggregate to form cataracts39... 

During the last ten years, it has become apparent that calcium-dependent papain-like peptidases called calpains (EC 3.4.22.17) represent an important intracellular nonlysosomal enzyme system [35][36], These enzymes show limited proteolytic activity at neutral pH and are present in virtually every eukaryotic cell type. They have been found to function in specific proteolytic events that alter intracellular metabolism and structure, rather than in general turnover of intracellular proteins. Calpains are composed of two nonidentical subunits, each of which contains functional calcium-binding sites. Two types of calpains, i.e., /i-calpain and m-calpain (formerly calpain I and calpain II, respectively), have been identified that differ in their Ca2+ requirement for activation. The activity of calpains is regulated by intracellular Ca2+ levels. At elevated cytoplasmic calcium concentrations, the precursor procal-pain associates with the inner surface of the cell membrane. This interaction seems to trigger autoproteolysis of procalpain, and active calpain is released into the cytoplasm [37]. 

This enzyme [EC 3.4.22.17] is an intracellular, nonlyso-somal member of the peptidase family C2. The enzyme catalyzes the calcium ion-dependent hydrolysis of peptide bonds with preference for Tyr-Xaa, Met-Xaa, or Arg-Xaa with a leucyl or valyl residue at the P2 position. There are two main types of calpain. One has a high calcium sensitivity in the micromolar range and is called (,-calpain or calpain I. The other calpain has a low calcium sensitivity in the millimolar range and is called m-calpain or calpain II. Forms of calpain exhibiting intermediate calcium sensitivity also exist. 

Myocardial infarction Ca2+ homeostasis is lost in ischemic areas, triggering inappropriate calpain activity desmin and a-spectrin are degraded in ischemic heart tissue by synthetic calpain inhibitors protein and mRNA levels of m-calpain and j,-calpain increase after myocardial infarction. Papp et al., 2000 Sandmann, et al., 2001 Tsuji, et al., 2001 Yoshida, et al., 2001... 

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. 

Figure 1. 3D structure of heterodimeric m-calpain, from Suzuki et al., 2004 (See Colour Plate 2)... 

Blomgren, K., Zhu, C., Wang, X., et al., 2001, Synergistic activation of caspase-3 by m-calpain after neonatal hypoxia-ischemia a mechanism of pathological apoptosis , J. Biol. Chem., 276, 10191-10198... 

Jia, Z., Petrounevitch, V., Wong, A., Moldoveanu, T., Davies, P.L., Elce, J.S., and Beckmann, J.S., 2001, Mutations in calpain 3 associated with limb girdle muscular dystrophy analysis by molecular modeling and by mutation in m-calpain., Biophys. J., 80, 2590-2596... 

McClelland, P., Lash, J., Hataway, D., 1989, Identification of major autolytic cleavage sites in the regulatory subunit of vascular Calpain II. A comparison of partial amino-terminal sequences to deduced sequence from complementary DNA, J. Biol. Chem., 264, 17428—17431 Mellgren, R., Song, K., Mericle, M., 1993, m-Calpain requires DNA for activity on nuclear proteins at low calcium concentrations, J. Biol. Chem., 268, 653—657 Melloni, E., Michetti, M., Salamino, F., Pontremoli, S., 1998, Molecular and functional properties of a calpain activator protein specific for [L-isoforms, J. Biol. Chem., 273, 12827—12831 Moldoveanu, T., Hosfield, C., Lim, D., Elce, J., Jia, Z., Davies, P., 2002, A Calcium switch aligns the active site of calpain, Cell, 108, 649—660... 

Mouatt-Prigent, A., Karlsson, J.O., Agid, and Hirsch E.C., 1996, Increased M-calpain expression in the mesencephalon of patients with Parkinson s disease but not in other neurodegenerative disorders involving the mesencephalon a role in nerve cell death, Neuroscience, 73, 979—987 Mundo, E., Soldati, L., Bellodi, L., Bianchi, G., 1997, The calpain-calpastatin system in obsessive-compulsive disorder, Biol. Psychiatry 42, 228—229... 

Thompson, V.F., and Goll, D.E., 2000, Purification of mu-calpain, m-calpain, and calpastatin from animal tissues, Methods. Mol. Biol., 144, 3-16... 

Fig. 17.2 (A) Effect of m-calpain on the activity and protein degradation of cardiac NMT. (B) Effect of calpastatin on cardiac NMT. For details see Raju et al. (1998).

Raju, R. V., Kakkar, R., Datla, R. S., Radhi, J., and Sharma, R. K. 1998. Myristoyl-coA protein N-myristoyltransferase from bovine cardiac muscle molecular cloning, kinetic analysis, and in vitro proteolytic cleavage by m-calpain. Exp. Cell Res. 241 23-35. 

There are two types of calpains, /tr-calpain and m-calpain, which require an in vitro calcium concentration at pM and mM level, respectively. This calcium-binding affinity is too low to bind calcium at cytoplasmic calcium concentration. However, an in vivo target molecule or other factors that enhance the calcium binding of calpains have not been identified. It is interesting to note that m-calpain is able to function at calcium concentrations less than 10 pM in the presence of excess high concentration of isovalerylcamitine (a ratio of 20 000 mol isovalerylcamitine to 1 mol calpain). ... 

Both p- and m-calpain comprise two chains, one light chain (domain VI) and a heavy chain (domain I-IV). Sequence analysis has revealed a possible EF-hand motif located... 

Chen, F., Lu, Y., Kuhn, D.C., Maki, M., Shi, X., Sun, S.C., and Demers, L.M., Calpain contributes to silica-induced I kappa B-alpha degradation and nuclear factor-kappa B activation, Arch. Biochem. Biophys., 342, 383-388, 1997. 

Shiraha, H., Glading, A., Chou, J. et al. (2002). Activation of m-calpain (calpain II) by epidermal growth factor is Umited by protein kinase A phosphorylation of m-calpain. Mol. Cell Biol. 22, 2716-2727. 

In the muscle, there are lysosomal cathepsins B, D, H and L, which are most active in acidic pH, sarcoplasmic m- and m-calpains, which are activated by Ca and exhibit most activities in neutral pH, and a proteasome dependent on ATP for activation. 

From these results, it might be concluded that both m- and m-calpains and cathepsins B and L are responsible for the increase in peptides concentrations at the ultimate pH (5.5-5.8) during postmortem aging of meat. 

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