Calpain is an intracellular Ca2+-dependent cysteine protease, requiring calcium ions for activity. Under these physiological conditions, a transient and localized influx of calcium into the cell activates a small local population of calpains (for example, those close to Ca2+ channels), which then advance the signal transduction pathway by catalyzing the controlled proteolysis of its target proteins. Other reported roles of calpains are in cell function, helping to regulate clotting and the diameter of blood vessels, and playing a role in memory. Calpains have been implicated in apoptotic cell death, and appear to be an essential component of necrosis.
Calpains, a family of Ca2+-dependent cytosolic cysteine proteases, can modulate their substrates' structure and function through limited proteolytic activity. In the human genome, there are 15 calpain genes. The most-studied calpains, referred to as conventional calpains, are ubiquitous. For treatment of these diseases, calpain inhibitors have always been considered as drug targets. Recent studies have introduced another aspect of calpains that calpain activity is required to protect the heart and skeletal muscle against stress.