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Hi Jorge, using a system where you can cleave off the His-tag (with TEV, FactorX, etc) adds a purification step which is complementary to the first purification step (Ni-column etc). In my experience this results in very pure protein which makes it more likely to crystallise. Therefore I would always choose such a system and not spend much time on trying to crystallise the protein with the His-tag attached. Tim -- Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A On Tue, 11 Nov 2008, [log in to unmask] wrote: > Dear all, > > Concerning the crystallization of proteins with a His-tag, based > upon discussions on this bulletin board and on the article > > Mike Carson, David H. Johnson, Heather McDonald, Christie Brouillette > and Lawrence J. DeLucas, His-tag impact on structure, Acta Cryst. D63, > 295-301, (2007). > > I understand that as a general approach one should try to > crystallize the protein with the His-tag (yet it might crystallize, so > no need to care the work of taking out the tag); then, if this is not > successful, go to the procedure to either express (and purify) it > without the His tag or take it out later. Any observations/advices? > But one other question to add is what if the protein is expressed > with both a c-myc tag and a His-tag (you might consider also the case > in which only the c-myc tag is present). Any experience on the effect of > the c-myc tag on crystallization? References are welcome yet I could not > find much googling around... > Thanks, > > Jorge