Applications of a peptide ligand for streptavidin: the Strep-tag

The Strep-tag constitutes a nine amino acid-peptide that binds specifically to streptavidin and occupies the same pocket where biotin is normally comp lexed. Since the Strep-tag participates in a reversible interaction it can be applied for the efficient purification of corresponding fusion proteins on affinity columns with immobilized streptavidin. Elution of the bound rec ombinant protein can be effected under mild buffer conditions by competitio n with biotin or a suitable derivative. In addition, Strep-tag fusion prote ins can be easily detected in immunochemical assays, like Western blots or ELISAs, by means of commercially available streptavidin-enzyme conjugates. The Strep-tag/streptavidin system has been systematically optimized over th e past years, including the engineering of streptavidin itself. Structural insight into the molecular mimicry between the peptide and biotin was furth ermore gained from X-ray crystallographic analysis. As a result the system provides a reliable and versatile tool in recombinant protein chemistry. Ex emplary applications of the Strep-tag are discussed in this review. (C) 199 9 Elsevier Science B.V. All rights reserved.