[Calpain and calpastatin].
Calpain is a Ca2(+)-dependent cysteine endopeptidase and calpastatin is a calpain-specific endogenous inhibitor protein. Both calpain and calpastatin are very widely distributed in various animal tissues and cells. Low (microM) Ca2(+)-requiring calpain I and high (mM) Ca2(+)-requiring calpain II are known to exist. Calpain consists of one heavy (80 kDa) and one light (30 kDa) subunit. The heavy subunits of calpains I and II are different genetic products, whereas the light subunits are the same for both calpains I and II. Molecular cloning as well as protein sequencing revealed that the heavy subunit has four domains, while the light subunit has two domains. The carboxyl terminal domain of each subunit is a calmodulin-like domain, whereas the catalytic site is located in domain 2 of the heavy subunit. Calpastatin has four internally repetitive inhibitory domains. A single domain, or even a truncated 27-mer fragment thereof, possesses inhibitory activity against calpains. Calpain shows a rather broad substrate specificity. It can cleave various enzymes, and cytoskeletal, membrane and receptor proteins. Calpain-catalyzed activation of protein kinase C and transglutaminase may represent a few of the physiological functions of calpain, but a great many other functions can be assigned as well to calpain. Immunohistochemical studies revealed very wide but quite diverse distribution of calpains I and II and calpastatin among various tissues and cells. The expression of the genes for calpain and calpastatin is found to be modulated by retrovirus (HTLV-I) infection to T-lymphocytes. The physiological significance of the calpain and calpastatin system is yet to be elucidated, and accumulating information definitely suggested the role of calpain/calpastatin in health and disease.
Murachi
T
T
Department of Clinical Science and Laboratory Medicine, Kyoto University Faculty of Medicine.
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D015394:Molecular Structure; D051381:Rats; D013379:Substrate Specificity; D013552:Swine
D002135:Calcium-Binding Proteins; D015853:Cysteine Proteinase Inhibitors; C033668:calpastatin; D002154:Calpain; D002118:Calcium