An Overview of S-Tags

What is S-tag?

S-tag is the name of an oligopeptide derived from pancreatic ribonuclease A (RNase A). The S-Tag is a novel fusion peptide tag for recombinant proteins that allows detection by a rapid, sensitive homogeneous assay or by colorimetric detection in Western blots. Proteins can also be rapidly purified from crude extracts using a one step affinity separation method.

Fig 1. S Tags for Protein Purification

If RNase A is digested with subtilisin, a single peptide bond is cleaved, but the resulting two products remain weakly bound to each other and the 15-amino-acid peptide carrying the amino-terminal sequence of RNase A (S-tag) can bind with high affinity to S-protein (residues 21–124 of the same RNase). These 15 amino acids long peptide is called S15 or S-tag. Although neither S-tag nor S-protein alone possesses any RNase activity, the complex of these two fragments is almost as active as intact RNase A. The two fragments derived from the corresponding regions of RNase 1 (called here human S-tag and S-protein) can also interact with similar affinity and regenerate the RNase activity.