Cystatin

The cystatins are a family of cysteine protease inhibitors which share a sequence homology and a common tertiary structure of an alpha helix lying on top of an anti-parallel beta sheet. The family is subdivided as described below.

Proteinase inhibitor I25, cystatin
Crystal structure of an immunomodulatory salivary cystatin from the soft tick Ornithodoros moubata from PDB entry 3L0R.
Identifiers
SymbolProt_inh_cystat
PfamPF00031
Pfam clanCL0121
InterProIPR000010
SMARTSM00043
PROSITEPDOC00259
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
PDBPDB: 1a67 PDB: 1a90 PDB: 1cew PDB: 1cyu PDB: 1cyv PDB: 1dvc PDB: 1dvd PDB: 1eqk PDB: 1g96 PDB: 1gd3

Cystatins show similarity to fetuins, kininogens, histidine-rich glycoproteins and cystatin-related proteins. Cystatins mainly inhibit peptidase enzymes (another term for proteases) belonging to peptidase families C1 (papain family) and C13 (legumain family). They are known to mis-fold to form amyloid deposits and are implicated in several diseases.

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