A novel aspect of calpain activation.

Calpain, a Ca2+-dependent biomodulator, alters the properties of substrate proteins by cleaving them at a limited number of specific sites. Recent studies of the structure-function relationship of calpain and X-ray analysis of its Ca2+-binding domain have revealed hitherto unknown features of the regulation of calpain activity. A novel dissociation/autolysis mechanism for the activation of calpain at the membrane is proposed, which incorporates recent findings from structure-function studies of calpain, and its implications are discussed.