Abstract
BACKGROUND: Feruloyl esterase is a multifunctional esterase with potential industrial applications. In the present study, we found the Lactobacillus amylovorus feruloyl esterase (FaeLam) could be secreted by L. plantarum and Escherichia coli. However, no signal peptide was detected in this protein as predicted by SignalP-5.0. Therefore, experiments were carried out to propose an explanation for the extracellular release of FaeLam. RESULTS: Here, we identified that the FaeLam could be secreted to the culture medium of L. plantarum CGMCC6888 and E. coli DH5α, respectively. To exclude the possibility that FaeLam secretion was caused by its hydrolytic activity on the cell membrane, the inactive FaeLam(S106A) was constructed and it could still be secreted out of L. plantarum and E. coli cells. Furthermore, the truncated version of the FaeLam without the N-terminal residues was constructed and demonstrated the importance of the 20 amino acids of N-terminus (N20) on FaeLam secretion. In addition, fusion of heterologous proteins with N20 or FaeLam could carry the target protein out of the cells. These results indicated the N-terminus of FaeLam played the key role in the export process. CONCLUSIONS: We proved the N-terminus of L. amylovorus FaeLam plays an important role in its secretion by L. plantarum and E. coli. To our best knowledge, this is the first reported protein which can be secreted out of the cells of both Gram-positive and Gram-negative bacteria. Furthermore, the results of this study may provide a new method for protein secretion in L. plantarum and E. coli through fusion the target protein to N20 of FaeLam.