Protein purification by affinity tags

Chen Ho An chen at bsm.bioc.ucl.ac.uk
Sat Oct 31 13:43:55 EST 1998

Yu Wai Chen (ywc at mrc-lmb.cam.ac.uk) wrote:
: Hello,

: This is a general question about making fusion protein for affinity
: purification.  Several protein purification systems offer a choice of N-
: or C- terminal fusion of affinity tags, such as CBD, His6 etc while
: other systems have only N-terminal tags, such as GST, MBP.  It is
: obvious that if the tag is at the N-terminus, one can get truncated
: protein products bound onto the affinity column.  If the tag is
: C-terminal, only full-length fusion protein will be retented.  With such
: consideration, why would so many affinity tags be made to the
: N-terminus?  It seems to me that it offers no advantage at all...

: Please comment.

Some proteins are not functional with a C-terminal His-tag, and I know of
some that cleaves itself at the C-terminus (therefore you lose the tag).
There are many other reasons why one would choose a N-terminus tag -
e.g. improved expression etc.  You choose whichever works or works best.

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