Comparison of Different Signal Peptide Targeting EGFP Translocation Periplasm in Salmonella

The signal peptide sequence of Salmonella OsmY and OmpA proteins as well as beta-lactamase (Bla) was synthesized and cloned into the Nco I/Nde I site of plasmid pET28a-EGFP, resulting in the construction of plasmid pET28a-OsmY-EGFP, pET28a-OmpA-EGFP, and pET28a-Bla-EGFP, respectively. Followed by transfermation into the wild-type Salmonella strain TT-1, the signal peptide fused EGFP were expressed in the presence of 0.5% isopropyl β-D-thiogalactopyranoside (IPTG). The localization of EGFP in Salmonella was determined by periplasmic protein quantification, fluorescence microscopy and the measurement of fluorescence intensity. The signal peptide of OsmY, OmpA or Bla not only direct EGFP to the periplasm of Salmonella but also kept its activity. Amongest the three peptides, the signal peptide of OsmY was the most efficient, resulting in the highest level of EGFP in the periplasmic space of Salmonella. In the present study, we assessed the efficacy of the signal peptide of OsmY, OmpA or Bla in directing the EGFP to the periplasm of Salmonella. We suggested that the Sec pathway of Salmonella is capable of exporting heterologous proteins in an active form, and the signal peptide of OsmY could deliver EGFP to the periplasm of Salmonella effectively.