De Novo Designing a Novel Signal Peptide for Secretion of Neurturin to the Periplasmic Space of Escherichia coli

Neurotrophic factors, including neurturin, increase the life span of the neurons and prevent neuronal destruction. As recombinant expression of neurturin with 3 disulfide bonds in Escherichia coli leads to the formation of inclusion bodies in the cytoplasm, periplasmic production of it is preferred. Signal peptides naturally exist at the N-terminus of the most newly synthesized proteins and are responsible for determining the final destination of the proteins. In the present study for the first time a novel signal peptide was designed de novo to secret recombinant neurturin to the periplasmic space of E. coli through the Sec pathway. Also the efficiency of de novo designed signal peptide (D.D.SP) was compared with that of pelB signal peptide. Designing process was performed using experiences from previous optimization studies and several bioinformatics tools such as BioEdit 7.2 software and SignalP-5.0 server. The quantitative analysis of Western blotting bands by ImageJ software showed that about 82% of expressed neurturin was secreted to the periplasmic space by D.D.SP while only 44% of expressed neurturin was obtained in the periplasmic space when PelB was used as a signal peptide. Moreover, CD spectroscopy analysis showed that the structure of secreted recombinant neurturin has high similarity to the commercial one.