Cathepsin F, also known as CTSF, belongs to the cathepsin family. Cathepsins are papain family cysteine proteinases that represent a major component of the lysosomal proteolytic system. The CTSF gene is ubiquitously expressed, and it maps to chromosome 11q13, close to the gene encoding cathepsin W. CTSF is thought to play a role in normal protein catabolism, and because it is highly expressed in some cancer cell lines, it may be involved in degradative processes occurring during tumor progression. Recombinant human CTSF protein, fused to His-tag at N-terminus, was expressed in E.coli.