What are the possible effects of export (secretion, using a pMAL-p2 vector) on solubility/stability of the fusion?
Initiating export through the cytoplasmic membrane puts a fusion protein on a different folding pathway – the solubility or stability of a protein is determined by whether this folding pathway leads to a different 3-dimensional structure for the protein. Some proteins, like MBP itself, can fold properly either in the cytoplasm or when exported to the periplasm. However, the normal folding pathway for some proteins is incompatible with passage through the membrane, so the fusion protein gets stuck in the membrane and cannot fold properly; this can lead to degradation (Gentz et al, 1988, J. Bact. 170, 2212-20). Other proteins, especially ones that have multiple disulfide-bonds, only fold properly when exported (the E. coli cytoplasm is a reducing environment, and the proteins that catalyze disulfide bond formation are present in the periplasm)(Bardwell et al., 1991, Cell 67, 581-9). When this class of protein is expressed in the cytoplasm, it may fold improperly and become degraded or in
