Tag purification strategy
AC separates protein typically on the basis of interactions between ligands and local domains
of target proteins. The interactions are not interfered by other domains in most case. Therefore,
the tag purification strategy was invented to rapidly separate recombinant protein by fusion
expression and co-separation [25].
First the target protein is expressed with a tag protein in fusion form. Then the target protein
is purified using an affinity column that is specific to tag protein. After that if the tag needs to
be removed, a restrictive protease is used to hydrolyze the fusion protein and the freed tag is
finally be separated from target protein by running the same column once again.
The ideal tag protein should (1) have economical affinity chromatography media for conven‐
ient separation, (2) be very stable in bioactivity, and (3) have a good expressing property that
is helpful to increase the expression of target protein. Commonly used tags are GST tag, FLAG
tag, S tag, Strep tag, His tag, and so on.