expressed protein is 5-6kda bigger than

[Paul N Hengen]

Christoph H. Winter (chw at sirius.mgen.uni-heidelberg.de) wrote:

> In our group it was detected on a SDS-gel with a His-tagged scFv (should
> have 28 kD by calculation, showed ca. 33 kD) and a non-related smaller
> protein my colleque cloned. Maybe(!) it's caused by the positive charge
> the His carries, retarding the whole protein...?
.
.
> Citation of the QIAexpressionist, Appendix B:
> Some proteins with 6xHis tags attached run more slowly on SDS gels than
> equivalent untagged proteins, and may appear to be several kD larger than
> expected

Hmmm...maybe it's due to some slight contamination of the gel or the
buffer with metal ions and the 6xHis binds this (?). Has anyone tried
to add Zn2+ to purified His-tagged protein to see a mobility shift on a gel?

--
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