title: Site-directed activation of calpain is promoted by a membrane-associated natural activator protein.
abstract: Human erythrocytes contain a calpain activator protein with a molecular mass of approx. 40 kDa. The activator is present in association with the plasma membrane and promotes expression of calpain activity at a concentration of Ca2+ close to physiological values. The initial step of the activating mechanism involves association of the activator with calpain, followed by autoproteolytic activation of the proteinase in the presence of 1 microM Ca2+, at a rate identical to that induced by 1 mM Ca2+. In a reconstituted system, the activator binds to erythrocyte membranes, but not to phospholipid vesicles, suggesting the participation of an intrinsic membrane protein(s). In its membrane-associated form the activator selectively binds calpain, thus favouring interaction of the proteinase with the inner surface of plasma membranes. These results further confirm the importance of a natural activator protein in promoting intracellular activation of calpain under physiological conditions through a site-directed mechanism, which explains the high specificity of the proteinase for membrane of cytoskeletal proteins.
authors.affiliation: Institute of Biochemistry, University of Genoa, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Salamino
authors.forename: R
authors.initials: R
authors.lastname: De Tullio
authors.forename: P
authors.initials: P
authors.lastname: Mengotti
authors.forename: P L
authors.initials: PL
authors.lastname: Viotti
authors.forename: E
authors.initials: E
authors.lastname: Melloni
authors.forename: S
authors.initials: S
authors.lastname: Pontremoli
mesh_terms: D001665:Binding Sites; D001798:Blood Proteins / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D002154:Calpain / Q000097:blood*; D002850:Chromatography, Gel; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D007461:Iodoacetates / Q000378:metabolism; D019807:Iodoacetic Acid
chemical_list: D001798:Blood Proteins; D007461:Iodoacetates; D002154:Calpain; D002118:Calcium; D019807:Iodoacetic Acid