Remember that on a SDS-PAGE gel you get an approximate MW, not an
absolute MW. Depending on the sequence it can run different. I
remember an example where a change (not an addition!) of one amino
acid caused a 4 kDa change in MW. I have expressed a protein in the
Qiaexpress and the pTrcHis vectors, where the only difference is that
the pTrcHis protein has a 5 amino acid addition, the enterokinase
cleavage site. The pTrcHis protein runs at 21 kD, the Qiaexpress at 18
kD. The 6 His tail changes the protein quite a lot, so the message is:
never ever only rely on SDS-PAGE for MW!
Just my 5 cents worth...
Arnoud
On Wed, 25 Mar 1998 22:07:20 -0800, James Bassuk
<bassuk at u.washington.edu> wrote:
>>nonsense. his-tag won't by itself cause nothing more than an increase
>in MW of 600.
>>but, being a recombinant protein, all kinds of screwy things can happen.
>your question is too general because every protein would have an
>emperical answer.
>>Jim Bassuk
>U Washington
>Seattle
>>>On Tue, 10 Mar 1998 ct133 at columbia.edu wrote:
>>> Hi,
>>>> Does anybody know whether his-tagged protein expressed from pRSET
>> vector (Invitrogen) can migrate aberrantly on SDS-PAGE?
>>>> Thanks,
>>>> C. Tunyaplin
>>>>>