Strep-Tactin®XT

The newly engineered Strep-Tactin®XT has an improved binding affinity to Twin-Strep-tag® and Strep-tag®II and is more stable compared to Strep-Tactin®. Strep-Tactin®XT now enables new applications in the field of high throughput screening, batch purification, purification using denaturing conditions and protein interaction studies. It also provides higher protein yields compared to Strep-Tactin®. Simultaneously, Strep-Tactin®XT preserves all benefits of Strep-Tactin® for protein purification, e.g. high purity (> 95 %), physiological buffer conditions, mild elution, regeneration of the resin for re-use.

Get highly pure proteins with Strep-Tactin®XT Superflow resin

One of the key advantageous of the Strep-tag® system is to achieve unparalleled protein purity (> 95 %) after purification of recombinant proteins independent of the expression host. This makes is system advantegous to other affinity purification systems like His-tag.

This Strep-tag® system III with its new features makes the system suitable for additional applications:

New applications: Excellent performance:
  • High-throughput screening
  • Batch purification
  • Denaturating conditions
  • High protein yields and purity
  • Optimized elution profile for highly concentrated target protein


Strep-Tactin®XT purification cycle

Step 1: The cell lysate / culture supernatant is applied on the column.

Step 2: Once the tagged protein has bound specifically to Strep-Tactin®XT the host proteins are instantly washed away with moderate amounts of physiological wash buffer (Buffer W).

Step 3: Bound Twin-Strep-tag® protein is gently eluted by Buffer BXT (wash buffer containing 50mM biotin) which specifically competes for the biotin binding pocket.

Step 4: Regeneration of the column is achieved by the application of 10mM NaOH. Sodium hydroxide removes the biotin from the binding pocket. NaOH can be removed simply by applying Buffer W. Strep-Tactin®XT resin can be regenerated and re-used 3 to 5 times without loss in performance.

Comparison of His-tag:NiNTA and Strep-Tactin®XT:Twin-Strep-tag®

Shown is the comparison of two randomly chosen protein, which were either fused to 6xHis-tag or Twin-Strep-tag®. Protein were purified via NiNTA resin, which was done under optimal His-tag purification conditions, or via Strep-Tactin®XT resin using physiological buffer conditions on the right side, respectively. Both proteins show low background when purified using the Strep-tag® system.


Improved performance of the 3rd generation Strep-tag® system

Strep-Tacin®XT allows higher protein yields

Strep-Tactin®XT allows the purification of higher protein yields compared to Strep-Tactin®. This was determined by purification of different target protein on either Strep-Tactin® or Strep-Tactin®XT. The obtained protein yields were determined and compared in the graph below. Here, we found that Strep-Tactin®XT allows in average the purification of a 2-fold higher protein yield compared to Strep-Tactin®.

Strep-Tactin XT allows intensive washing without loss in yield

An advantage ot the new Strep-tag system III is that it allows intensive washing with loss of protein yields. This figure shows purification of mCherry-Twin-Strep-tag fusion protein on 1 ml Strep-Tactin Superflow resin and 1 ml Strep-Tactin XT Superflow resin. After prepared E. coli supernatants were applied onto the column, columns were washed with 8 CV Buffer W in order to reach a constant absorption at A260/A280 nm. Then the target protein was eluted with biotin. Samples of the last wash fraction and the elution fraction were analysed on SDS-PAGE showing that some of the target protein was washed down from Strep-Tactin Superflow resin, whereas no protein was eluted from Strep-Tactin XT Superflow resin.

The elution fractions were further analysed in Western Blot, showing that the remaining bands are degradation products of mCherry.