title: Calpastatin subdomains A and C are activators of calpain.
abstract: The inhibitory domains of calpastatin contain three highly conserved regions, A, B, and C, of which A and C bind calpain in a strictly Ca(2+)-dependent manner but have no inhibitory activity whereas region B inhibits calpain on its own. We synthesized the 19-mer oligopeptides corresponding to regions A and C of human calpastatin domain I and tested their effect on human erythrocyte mu-calpain and rat m-calpain. The two peptides significantly activate both calpains: the Ca(2+) concentration required for half-maximal activity is lowered from 4.3 to 2.4 microm for mu-calpain and from 250 to 140 microm for m-calpain. The EC(50) concentration of the peptides is 7.5 microm for mu-calpain and 25 microm for m-calpain. It is noteworthy that at low Ca(2+) concentrations (1-2 microm for mu-calpain and 70-110 microm for m-calpain) both enzymes are activated about 10-fold by the peptides. Based on these findings, it is suggested that calpastatin fragments may have a role in calpain activation in vivo. Furthermore, these activators open new avenues to cell biological studies of calpain function and eventually may alleviate pathological states caused by calpain malfunction.
authors.affiliation: Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, H-1518 Budapest, P. O. Box 7, Hungary. tompa@enzim.hu
authors.forename: Peter
authors.initials: P
authors.lastname: Tompa
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Mucsi
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Orosz
authors.forename: Peter
authors.initials: P
authors.lastname: Friedrich
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D002154:Calpain / Q000502:physiology*; D004789:Enzyme Activation; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000502:physiology*; D051381:Rats
chemical_list: D002135:Calcium-Binding Proteins; D010446:Peptide Fragments; C033668:calpastatin; D002154:Calpain; D002118:Calcium