epitope tag: two or one?

Bernard Murray bpmurray*STUFFER* at socrates.ucsf.edu
Wed Jun 17 22:13:37 EST 1998

In article <B1AC8668-1FD14 at>, rmeili_nospamare at hotmail.com wrote:

> Hi all,
> I am interested to hear what experience you have with a tandem repeat of an
> epitope tag like myc, HA, FLAG etc. Since an IgG has two binding sites the
> affinity should be much increased when compared to a single tag. 
> Is there any literature you know about? Should there be a spacer between
> the two tags? 
> Thanks a lot
> Ruedi

But IgG usually uses only one of its potential binding sites
for each target.  If you look at the structures of IgG obtained
after crystallisation the molecule is almost T-shaped (Y shaped
at best) rather than like the neat "tuning fork" shapes beloved
of textbooks so the binding sites are usually used for
separate target molecules.
     This being said, tandem binding sites may help as this
would permit more than one IgG to bind.  This would aid detection
if you are performing blotting/immunocytochemistry etc. or would
allow cross-linking and thus more efficient immunoprecipitation
if that is your aim.
     From my rusty memories I believe this represents an increase
in *avidity* rather than *affinity* (now where did I leave my
copy of Roitt..?)
     Good luck,
Bernard Murray, PhD
Dept. Cell. Mol. Pharmacol., UCSF, San Francisco, USA

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