Recombinant Mouse Cystatin E/M/CST6 is produced by our mammalian expression system in human cells. The target protein is expressed with sequence (Glu29-Val149) of Mouse CST6 fused with a polyhistidine tag at the C-terminus. Mouse CST6 is a member of the family 2 of the cystatin superfamily. The type 2 cystatin proteins are a class of cysteine proteinase inhibitors found in a variety of human fluids and secretions, where they appear to provide protective functions. CST6 is expressed in heart, liver and kidney. In addition to its function as a cysteine protease inhibitor, CST6 also serves as a target for cross-linking by transglutaminases. Accordingly, CST6 was suggested to be involved in barrier formation and maintenance. Furthermore, studies have revealed that CST6 is frequently epigenetically inactivated during breast carcinogenesis, and thus be regarded as a candidate of tumour suppressor gene.