[Protein-analysis] Why do disordered regions within proteins decrease expression yields?

[S.E. Hart]

Hi,

I've been trying to express a protein in the cytosol of E. coli. I'm only 
getting very low yields. The protein is predicted to contain a disordered 
region of at least 40 amino acids. Would this be enough to explain the low 
yields? The disordered region is at the very N-terminus - I truncated the 
protein in a loop region after two transmembrane regions. Why do 
disordered regions have a negative effect on expression yields - is it 
just because they are likely to be targets for proteases or are the other 
factors? I've found that adding a tag to the protein greatly increases the 
yields. Is that just because the disordered region is no longer at the 
N-terminus? I appreciate that tags can have other positive effects e.g. on 
the solubility of the protein.

Any help in this matter would be MUCH appreciated.

Thanks,
Sarah