Dear all,
I'm sorry if this is and old one, but I have just come across this
problem.
When trying to purify my protein from E. coli as a His-tag fusion, I end
up co-purifiying
a very abundant 25 Kda protein (according to SDS-PAGE and mass
spectrometry)
that elutes at the same imidazole concentrations.
My protein is found in inclusion bodies as well as in the soluble
extract, but the
contaminant is also found in the soluble and insoluble fractions.
I carried out an amino acid analysis and found plenty of histidines and
Asx + Glx.
The database shows that an E. coli peptidyl-prolyl isomerase of the
FKBP type has almost
the same percent composition, (and these proteins have been found to
bind to Ni2+
columns very tightly) but its Mw is only around 21 Kda.
FYI, I'm using the pLEX system (Invitrogen) in the GI724 E. coli strain.
If this subject is already in the FAQ, please let me know where can I
access to it.
Thank you very much
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Prof. J. M. Sanz
Centro de Biologia Molecular y Celular
Universidad Miguel Hernandez
E-mail: jmsanz at umh.es
WWW:http://cbmc.umh.es/jmsanz/jesussanz.htm
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