Multiple interactions of the 'transducer' govern its function in calpain activation by Ca2+.
Typical calpains in mammals become activated on binding of 8-12 Ca2+ ions per enzyme molecule, giving an example of integrated, manifold regulation by calcium. Besides two identified Ca2+ sites in catalytic domain II and several EF-hand motifs in domains IV and VI, an acidic loop in the centrally positioned domain III seems to harbour Ca2+. The mediator of distant Ca2+-induced structural transitions is an elongated structural element, the 'transducer'. By site-directed mutagenesis along the transducer, we have generated various forms of rat m-calpain in which critical intramolecular interactions, as judged from the X-ray structure, would be abolished or modified. The kinetic parameters of these mutant enzymes support a model featuring shrinkage of transducer as a contributor to structural changes involved in calpain activation.
Bozóky
Zoltán
Z
Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 7, 1518 Budapest, Hungary.
Alexa
Anita
A
Tompa
Peter
P
Friedrich
Peter
P
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D020013:Calcium Signaling / Q000502:physiology; D002154:Calpain / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D051381:Rats
D002154:Calpain; D002118:Calcium