I am working with a protein which becomes soluble thanks to MBP. I do not see much expression with GST and also see the contamination of GroEL when I overexpress with GST. However the protein solubilizes with MBP tag but very less fusion is obtained from BL21. In shuffle cells, I see a lot of protein come out in the superntant but they elute in the void volume in size exclusion. When I attempt to cleave the tag, the protein precipitates. I have tried different glycerol and salt concentrations but it does not seem to help. One of the suggestions I got was the use of a eukaryotic expression system. But since it would be convenient with bacteria I thought I should post this question. 

The fusion does not bind the affinity column efficiently. There are 13 cysteines in the construct. 

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