How to improve your Strep-tag® protein purification results:
Note, preparing a 50mM biotin solution is a time-consuming procedure which takes several hours. Therefore we recommend to buy our ready-to-use buffer BXT (#2-1042-025) if possible!
If you have to prepare the biotin solution your own you have to consider the following:
Contamination of biotin is often a problem during mammalian expression, when the protein is secreted into the medium. Mammalian expression media contain high amounts of biotin (vitamin H). Biotin will block the column and the Strep-tag®II or Twin-Strep-tag® target protein cannot bind to the resin. Therefore it needs to be blocked before it can be applied to a Strep-Tactin® or Strep-Tactin®XT column. For this the BioLock solution (Biotin blocking solution) can be used. Per 70 µg of biotin add 1 ml of this solution. Further information can be found here.
Intrinsic biotin or biotinylated proteins are only abundant in very low concentrations and do not disturb the purification process or the purity of the target protein. To completely avoid those proteins small amounts of Avidin or BioLock can be added.
In general the interaction of Strep-tag®II and Twin-Strep-tag® to Strep-Tactin®XT is quite stable and not influenced by detergents or other additives. A list of so far tested reagents can be found here.