Our proprietary Strep-tag® technology exploits one of the strongest non-covalent interactions in nature: the interaction of biotin and streptavidin. The system is based on the highly selective and easily controllable interaction between the synthetic Strep-tag®II peptide and the specially engineered streptavidin, called Strep-Tactin®, which is one of the most stable proteins known. The Strep-tag® binds specifically to streptavidin and its variants by occupying the binding pocket of the natural ligand biotin. Hence, the interaction is easily reversible by excessive addition of the competitor.
Two affinity tags – two streptavidin derivatives: The Strep-tag®II consists of eight amino acids (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys), whereas the Twin-Strep-tag® includes this motif two times in series connected by a linker and is accordingly composed of 28 amino acids. Both exhibit intrinsic, although unequal, affinity towards the streptavidin derivative Strep-Tactin® and its successor Strep-Tactin®XT: The binding affinity of Strep-tag®II to Strep-Tactin® (1µM) is nearly 100 times higher than to streptavidin. A further improvement was achieved by the development of Strep-Tactin®XT, which shares a nM affinity with the Strep-tag®II and a pM affinity with the Twin-Strep-tag®.
As a result of the differences in binding strength among the possible tag-ligand combinations, the Strep-tag® system has become established as a universal tool for isolation of proteins, cells, and exosomes.
- Fused to recombinant proteins, the Strep-tag®II or Twin-Strep-tag® enable efficient one-step purification on immobilized Strep-Tactin® or Strep-Tactin®XT.
- When fused to antibody-derived Fab fragments or nanobodies, Twin-Strep-tag® binds to multimerized Strep-Tactin® allowing capturing and releasing of target cells and exosomes based on their surface-marker or antigen-specificity.
- Strep-Tactin® (or Strep-Tactin®XT), on its turn, can be conjugated to microplates, fluorophores or chips, allowing a wide range of analytical applications after isolation of target material, such as detection, immobilization and interaction studies.
Key features of the Strep-tag® system are:
- Full functionality of target material after isolation
- High purities
- Universal applicability for various analytic applications
- Simple purification procedures