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. aggregation-resistant) 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 non-specific 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.