The Strep-tag system is a method which allows the purification and detection of proteins by affinity chromatography. The Strep-tag is a synthetic peptide consisting of eight amino acids (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys). This peptide sequence exhibits intrinsic affinity towards Strep-Tactin, a specifically engineered streptavidin and can be N- or C- terminally fused to recombinant proteins. By exploiting the highly specific interaction, Strep-tagged proteins can be isolated in one step from c