The protein encoded by this gene is an endogenous calpain (calcium-dependent cysteine protease) inhibitor. It consists of an N-terminal domain L and four repetitive calpain-inhibition domains (domains 1-4), and it is involved in the proteolysis of amyloid precursor protein. The calpain/calpastatin system is involved in numerous membrane fusion events, such as neural vesicle exocytosis and platelet and red-cell aggregation. The encoded protein is also thought to affect the expression levels of genes encoding structural or regulatory proteins. Alternatively spliced transcript variants encoding different isoforms have been described.,CAST,BS-17,PLACK,Epigenetics & Nuclear Signaling,RNA Binding,Cell Biology & Developmental Biology,Ubiquitin,Neuroscience,Cell Type Marker,Neurodegenerative Diseases,Amyloid Plaque and Neurofibrillary Tangle Formation in Alzheimer's Disease,Neuron marker,Synapse marker,CAST