The Strep-tag system for one-step purification and high-affinity detection or capturing of proteins

The Strep -tag II is an eight-residue minimal peptide sequence (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys) that exhibits intrinsic affinity toward streptavidin and can be fused to recombinant proteins in various fashions. We describe a protocol that enables quick and mild purification of corresponding Strep -tag II fusion proteins—including their complexes with interacting partners—both from bacterial and eukaryotic cell lysates using affinity chromatography on a matrix carrying an engineered streptavidin ( Strep -Tactin), which can be accomplished within 1 h. A high-affinity monoclonal antibody ( Strep MAB-Immo) permits stable immobilization of Strep -tag II fusion proteins to solid surfaces, for example, for surface plasmon resonance analysis. Selective and sensitive detection on western blots is achieved with Strep -Tactin/enzyme conjugates or another monoclonal antibody ( Strep MAB-Classic). Thus, the Strep -tag II, which is short, biologically inert, proteolytically stable and does not interfere with membrane translocation or protein folding, offers a versatile tool both for the rapid isolation of a functional gene product and for its detection or molecular interaction analysis.