Calpains: Diverse Functions but Enigmatic.

Calpains are a group of non-lysosomal Ca2+ -dependent cysteine proteases with numerous substrates. Calpains have been identified in almost all eukaryotes and bacteria but not in archaebacteria. In the human genome, this group of enzymes has 15 isoforms and is present ubiquitously and demonstrates tissue-specific patterns of expression. Calpains are involved in different physiological and pathological processes such as cell proliferation, migration, invasion, apoptosis and signal transduction and their roles in various disorders have been reported. In this review, functions of calpains, their substrates, their mechanism of regulation and their involvement in diseases have been summarized.