Abstract
BackgroundFeruloyl 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.ResultsHere, 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 FaeLamS106A 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.ConclusionsWe 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.
Highlights
Feruloyl esterase is a multifunctional esterase with potential industrial applications
We reported that the feruloyl esterase FaeLam from L. amylovorus CGMCC11056 could be secreted from L. plantarum CGMCC6888 and E. coli DH5α respectively when heterologously overexpressed by Lactobacillus/E. coli shuttle vector
This vector had a promoter Ptuf, which had been verified to FaeLam is secreted by L. plantarum and E. coli without typical signal peptide We previously reported that L. amylovorus CGMCCC11056 was capable to produce feruloyl esterase FaeLam, which consists of 247 amino acids with a molecular mass of 27.4 kDa [17]
Summary
Feruloyl esterase is a multifunctional esterase with potential industrial applications. Considering the importance in various applications, many feruloyl esterases have been found and isolated from a large number of fungal and bacterial sources [4]. More and more feruloyl esterases have been identified and characterized in different Lactobacillus species, which have generally recognized as safe (GRAS) status and long history of use in food applications [5]. Given the essential role of feruloyl esterase in the production of hydroxycinnamic acids, plus the GRAS status of Lactobacillus species, which have less regulatory concerns, feruloyl esterases from probiotic Lactobacillus strains can be directly used for increased production of high-value hydroxycinnamates and ferulic acid from natural or synthetic carbon sources [6]. Lactobacillus feruloyl esterases are heterologously expressed in host cells and purified for applications. Whether feruloyl esterase can be secreted by Lactobacillus strains is still unknown [6, 7]
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