Molecular and functional properties of a calpain activator protein specific for mu-isoforms.
A natural calpain activator protein has been isolated from bovine brain and characterized in its properties and molecular structure. The protein is a homodimer with a molecular mass of about 30 kDa and results in being almost identical to UK114 goat liver protein. Significant similarities with mouse HR12 protein were also observed, whereas a lower degree of similarity was found with a family of heat-responsive proteins named YJGF and YABJ from Haemophilus influenzae and Bacillus subtilis, respectively. The brain activator expresses a strict specificity for the mu-calpain isoform, being completely ineffective on the m-calpain form. As expected, also UK114 was found to possess calpain-activating properties, indistinguishable from those of bovine brain activator. A protein showing the same calpain-activating activity has been also isolated from human red cells, indicating that this factor is widely expressed. All these activators are efficient on mu-calpain independently from the source of the proteinase. The high degree of specificity of the calpain activator for a single calpain isoform may be relevant for the understanding of sophisticated intracellular mechanisms underlying intracellular proteolysis. These data are indicating the existence of a new component of the Ca2+-dependent proteolytic system, constituted of members of a chaperonin-like protein family and capable of promoting intracellular calpain activation.
Melloni
E
E
Institute of Biological Chemistry, University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy. melloni@csita.unige.it
Michetti
M
M
Salamino
F
F
Pontremoli
S
S
D000595:Amino Acid Sequence; D000818:Animals; D002154:Calpain / Q000378:metabolism*; D002417:Cattle; D002852:Chromatography, Ion Exchange; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D007527:Isoenzymes; D002154:Calpain; D003546:Cysteine Endopeptidases