Dear Pascal,
be aware that fos-choline detergents are extremely efficient solubilizers of
membrane proteins. We found that even partially aggregated membrane proteins
could be solubilized with fos-choline 12, while this fraction did sediment
using for example dodecylmaltoside (see e.g. fig5 and sfig2 of
PNAS,2008;105(15):5722-7; PMID: 18391190). Thus, it might be that your protein
is not expressed in a well-folded state, but that it is (partially) aggregated
thereby obscuring the His-tag and preventing binding to the column. To
determine whether this is the case you could put a fraction of your high-spin
supernatant after solubilization on SEC column and detect the protein by
immunoblotting the fractions. If most of the protein elutes in the void this is
a strong indication that your protein is not expressed in a good state.
Good luck,
Eric
