CSTA, also known as Stefin A, is thiol protease inhibitors that form complexes with papain and the cathepsins B, H and L. The protein is one of the precursor proteins of the cornified cell envelope in keratinocytes and plays a role in epidermal development and maintenance. CSTA is thought to be a tumor suppressor, since an inverse correlation seems to exist between the level of CSTA and tumor progression, in several malignancies Recombinant human CSTA protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.