Encoding Kininogen proteins, Kininogen Family Genes belong to the Cystatin Superfamily, a single evolutionary superfamily of three inhibitory subfamilies that encode proteins with likely protective function and structural similarities that include cystatin-like sequences: Stefins (Type 1 Cystatins), Cystatins (Type 2 Cystatins), and Kininogens. Many members are active cysteine protease inhibitors; others have lost or never acquired inhibitory activity. Kininogens contain 3 cystatin-like domains, each with 2 disulfide bonds. Type 2 Cystatins contain multiple cystatin-like domains and have 2 intrachain disulfide bonds. Type 1 Cystatins contain multiple cystatin-like domains and lack disulfide bridges. (NCI) [ ]