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