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Keywords:

  • organophosphorus hydrolase;
  • periplasmic translocation;
  • twin-arginine translocation pathway;
  • molecular chaperone;
  • whole-cell biocatalyst

Abstract

Periplasmic secretion has been used in attempts to construct an efficient whole-cell biocatalyst with greatly reduced diffusion limitations. Previously, we developed recombinant Escherichia coli that express organophosphorus hydrolase (OPH) in the periplasmic space using the twin-arginine translocation (Tat) pathway to degrade environmental toxic organophosphate compounds. This system has the advantage of secreting protein into the periplasm after folding in the cytoplasm. However, when OPH was expressed with a Tat signal sequence in E. coli, we found that the predominant OPH was an insoluble premature form in the cytoplasm, and thus, the whole-cell OPH activity was significantly lower than its cell lysate activity. In this work, we, for the first time, used a molecular chaperone coexpression strategy to enhance whole-cell OPH activity by improving the periplasmic translocation of soluble OPH. We found that the effect of GroEL-GroES (GroEL/ES) assistance on the periplasmic localization of OPH was secretory pathway dependent. We observed a significant increase in the amount of soluble mature OPH when cytoplasmic GroEL/ES was expressed; this increase in the amount of mature OPH might be due to enhanced OPH folding in the cytoplasm. Importantly, the whole-cell OPH activity of the chaperone–coexpressing cells was ∼5.5-fold greater at 12 h after induction than that of cells that did not express the chaperone as a result of significant Tat-based periplasmic translocation of OPH in the chaperone–coexpressing cells. Collectively, these data suggest that molecular chaperones significantly enhance the whole-cell activity of periplasmic OPH-secreting cells, yielding an effective whole-cell biocatalyst system with highly reduced diffusion limitations. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 28: 925–930, 2012