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Avidin is a tetrameric biotin-binding protein with a KD of ~1 x 10-14 and is extracted from egg white. It prevents biotin and biotinylated proteins from binding to Strep-Tactin® or Strep-Tactin®XT, whereas binding of the Twin-Strep-tag® and Strep-tag®II is not influenced. Biotin and biotinylated proteins can potentially reduce the binding capacity of Strep-Tactin® and Strep-Tactin®XT and are present in cell lysates and cell culture media, especially from insect or mammalian cells.
Thus, if Twin-Strep-tag® and Strep-tag®II fusion proteins from biotin-containing extracts or media are intended to be purified via Strep-Tactin® or Strep-Tactin®XT affinity chromatography, biotin has to be masked by the addition of avidin prior to application onto the resin.
Biotin Blocking Buffer can be prepared for western blotting by dissolving 2.5 mg/ml Avidin in PBS buffer.
