Normally this protein EIF4E is expressed untagged and expresses in inclusion bodies that are refolded through dialysis, but its very long winded and likes to precipitate during dialysis resulting in a low yield.
I have a GST tagged version that expresses better and is in the soluble phase, what i am wondering is it possible for the GST tag to be folded correctly with the EIF4E part being unfolded or if its in the soluble phase is it all likely to be folded correctly?
I would cleave the tag and purify the cleaved protein using size exclusion chromatography. If you can elute a monomeric fraction, I would check the integrity of its fold using CD spectroscopy and test for aggregation with DLS. As you have the refolded protein available, you can easily compare the spectra of both. If available, NMR is also a nice way to check for properly folded protein.
Ad Sebastian told may happen that tag as gst, mbp are able to produce also unfolded proteins but it depends from protein to protein. With gst in the past i succeded to express and purify several proteins there where folded and functional. As Joanh suggest of you have an enzime for tag removal you can go on with tag cleavage and see whats happen. in my experience in most cases of your protein is unfolded the cleavage will fail because the unfolded part induce formation of soluble aggregates and the enzime ia not able to reach the digestion site which is masked from the tag or in case that digestion succedd once the tag is cleaved the protein precipitate. So go on with your process and see whats happen.
good luck
Manuele
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