 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.