Cystatin-B (CSTB) Human Active Protein

The cystatin superfamily encompasses proteins that contain multiple cystatin-like sequences. Some of the members are active cysteine protease inhibitors, while others have lost or perhaps never acquired this inhibitory activity. There are three inhibitory families in the superfamily, including the type 1 cystatins (stefins), type 2 cystatins and kininogens. This gene encodes a stefin that functions as an intracellular thiol protease inhibitor. The protein is able to form a dimer stabilized by noncovalent forces, inhibiting papain and cathepsins l, h and b. The protein is thought to play a role in protecting against the proteases leaking from lysosomes. Evidence indicates that mutations in this gene are responsible for the primary defects in patients with progressive myoclonic epilepsy (EPM1). [provided by RefSeq, Jul 2008]

CSTB: This is an intracellular thiol proteinase inhibitor. Tightly binding reversible inhibitor of cathepsins L, H and B. Defects in CSTB are the cause of progressive myoclonic epilepsy type 1 (EPM1). EPM1 is an autosomal recessive disorder characterized by severe, stimulus-sensitive myoclonus and tonic-clonic seizures. The onset, occurring between 6 and 13 years of age, is characterized by convulsions. Myoclonus begins 1 to 5 years later. The twitchings occur predominantly in the proximal muscles of the extremities and are bilaterally symmetrical, although asynchronous. At first small, they become late in the clinical course so violent that the victim is thrown to the floor. Mental deterioration and eventually dementia develop. Belongs to the cystatin family.

Protein type: Inhibitor

Chromosomal Location of Human Ortholog: 21q22.3

Cellular Component: extracellular space; cytoplasm; nucleolus

Molecular Function: protease binding; endopeptidase inhibitor activity; cysteine protease inhibitor activity

Biological Process: negative regulation of proteolysis; regulation of apoptosis; adult locomotory behavior; negative regulation of peptidase activity

Disease: Myoclonic Epilepsy Of Unverricht And Lundborg