Evaluation the Therapeutic Index of Recombinant Antimicrobial S3 Tetramer-Peptides Expressed in E. coli

There is still a long way to go to commercialize antimicrobial peptides (AMPs) due to critical issues like efficiency, safety, and production costs. Through previous work, we demonstrated that using glycine–serine and aspartic acid–proline linkers for tandem repeated gene expression of S3 AMP resulted in improved antimicrobial activity of tetramer AMPs (named S3-4mer-GS and S3-4mer-DP, respectively). However, the impact of this production approach on the safety and therapeutic index (TI) of these tetramer peptides was not studied. In this research, S3-4mer-GS and s3-4mer-DP were expressed in E. coli BL 21(DE3) with expression rates of 35.5% and 36.8%, respectively. The safety was evaluated by assessing the hemolytic activity of peptides on human erythrocyte cells. The minimum concentrations resulting in complete inhibition of bacterial growth (MIC) were determined. The MIC of S3-4mer-GS was found to be slightly higher than S3-4mer-DP (1.2 fold). The hemolytic activity of S3-4mer-GS was 3.3 fold less than that of S3-4mer-DP and was directly related to the mean hydrophobicity index. The TI of S3-4mer-GS was 3.91 and 10.71 fold higher than S3-4mer-DP and S3 monomer, respectively. According to these results, tandem repeated gene expression using glycine–serine linker could be considered as an effective solution for large-scale production of S3 tetramer peptide with modified therapeutic index.