Chaperone-Mediated Protein Folding Enhanced D-Psicose 3-Epimerase Expression In Engineered Bacillus Subtilis

Functional mature proteins usually undergo folding, and in vivo folding is often affected by factors such as translation ratio, intracellular environment, and chaperones. D-psicose 3-epimerase (DPEase) derived from Dorea sp. has excellent properties in catalytic production of D-allulose; a rare sugar with unique biological functions. Here, the Dorea sp. DPEase coding gene was fusion-expressed with four native chaperones (DnaK, DnaJ, GrpE and PrsA) in Bacillus subtilis, and resulted in an 4.31- and 6.12-fold increase to 10.81 U/g and 13.34 U/g in recombinant cells of BS-DPE-DnaK and BS-DPE-PrsA, respectively. The recombinant proteins showed increased thermostability without significant change in the optimum pH and Co2+ affinity. Using recombinant cells as catalysts, a 1.12-2.31-fold increase was detected in DPEase activity after treatment with 40 % ethanol. We showed that fusion expression of molecular chaperones to enhance protein-assisted folding could facilitate expression of DPEase. We hope that our results provide a facilitated route for large-scale production of D-allulose in B. subtilis.