Solubilization of aggregation-prone heterologous proteins by covalent fusion of stress-responsive Escherichia coli protein, SlyD

The proteome profile of Escherichia coli BL21(DE3) generated in response to heat shock stress was analyzed by two-dimensional electrophoresis (2-DE), wherein we identified a FKBP-type peptidyl–prolyl cis–trans isomerse (PPIases), SlyD, as a stress-responsive (i.e. aggregationresistant) protein. Even under an imposed severe stress condition where 29 out of 858 soluble proteins were totally eliminated and the synthesis levels of 171 proteins decreased over 5-fold, a 3.37-fold increase induced by heat shock treatment was observed in the synthesis level of SlyD compared with a non-stress condition. As a fusion partner, as well as solubility enhancer, SlyD facilitated folding and significantly increased the solubility of many aggregation-prone heterologous proteins in E. coli cytoplasm. SlyD was very effective in sequestering interactive surfaces of heterologous proteins associated with nonspecific protein–protein interactions and the formation of inclusion bodies, most likely as a result of intrinsic folding efficiencies and/or chaperone-like activities. SlyD was also shown to be suitable for the production of a biologically active fusion mutant of Pseudomonas putida cutinase that is of considerable biotechnological and commercial interest.