Strep•Tag technology is based on the strong and specific interaction between biotin and streptavidin. To take advantage of this interaction for recombinant protein affinity purification, an 8-amino acid Strep•Tag II peptide that is capable of binding to the biotin pocket of streptavidin was engineered. Likewise, the Strep•Tactin ® protein, a streptavidin derivative, was developed for optimal Strep•Tag II peptide binding. The binding affinity of Strep•Tag II peptide for Strep•Tactin protein is nearly 100 times higher than for streptavidin. The Strep•Tactin family of products offers a wide variety of supports for rapid one-step affinity purification of proteins containing the Strep•Tag II fusion tag. The Strep•Tag II sequence binds to the Strep•Tactin coupled resin, and after unbound proteins are washed away, the purified target protein is competitively eluted with 2.5 mM desthiobiotin, a reversibly analog of biotin. The purification steps may be performed under physiological conditions in PBS or other physiological buffers preserving the bioactivity of the target protein. Using a simple and efficient cloning strategy provided by Novagen expression vector, the Strep•Tag II peptide can be fused to the N-terminus of a target protein. A selection of vectors enables protein expression in bacterial, insect, and mammalian systems.
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