Reconstruction and Optimized Expression of a Synthetic Secretory Leukocyte Protease Inhibitor (SLPI) Gene in Escherichia coli BL21

An active substance that has the greatest effect on wound healing is Secretory Leukocyte Protease Inhibitor (SLPI). It is known that the SLPI encoding genes can be isolated and expressed on amnion membrane. Previous studies, we isolated and optimized the SLPI gene through Echerrchia coli BL21 (DE3) mediated pET101/DTOPO, which expressed active recombinant human SLPI (rhSLPI) stored in pET-ESLPI. However, the expression of the rhSLPI products has not yet been accomplished. In this study, we optimized SLPI expression by developing a synthetic SLPI gene based on amino acid sequences with codons and expressed in E. coli BL21 to give the maximum expression. We used pUC57 and pET-32a plasmids to promote the cloning of synthetic SLPI genes. A codonoptimized SLPI gene was successfully synthesized with codon adaptation index value showing the distribution of codon usage frequency along the length of the gene sequence. In addition, the pET-SLPIopt fusion protein was successfully optimized with band sizes of 5900bp (pET-32a) and 413bp (SLPI) by double-digestion of NcoI and EcoI restriction enzymes. After the pET-SLPIopt was induced with various IPTG concentrations (50, 100, and 500 uM) at 30 °C, both soluble and insoluble fractions were analyzed as a result of SDS-PAGE which showed that the fusion protein, expressed predominantly in the supernatant, was 29.18 kDa. Our reported findings the recombinant protein of SLPI through pET-32a plasmid could be expressed in dissolved form.