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Introduction: Antimicrobial peptides (AMPs) are compounds with antimicrobial properties that are studied widely due to the development of resistance of pathogenic bacteria to antibiotics. In the present study, the toxicity and antimicrobial effects of two natural monomeric peptides (S3 and S∆3) were compared with S3-S∆3 hybrids and S3 tetramers. Material & Methods: Protein hybrids (S∆3S3-2mer-GS) S3-S∆3 and tetramer protein S3 (S3-4mer-GS) were expressed in E. coli. BL21 (DE3). Following that, the presence of mutant peptides was confirmed, and their antimicrobial activity was compared and evaluated with S3 and S∆3 monomers. Finally, the toxicity of tetramer and hybrid made on the MDA-MB-231 cell line was evaluated and compared. Findings: The toxicity of the hybrid was slightly increased, compared to the tetramer for eukaryotic cells; however, this increase was negligible at the active concentration of this protein. Cell survival for hybrids was lower for S3 and SΔ3; nonetheless, cell survival for each sequence decreased with increasing time. Furthermore, the inhibition of hybrid microbial growth was improved and compared with tetramer and S3-SΔ3. It was found that an increase in the positive charge of the hybrid protein did not have a toxic effect on the host bacteria. Discussion & Conclusion: Due to the appropriate expression and increased antimicrobial activity and negligible cytotoxicity, the hybrid peptide S3-S∆3 and tetramer S3 can be considered an effective production strategy to obtain AMPs.

Introduction: The study of the effects of synthetic peptides with antibacterial properties can provide more effective antibiotics. This study designed, expressed, and investigated the Sushi 3 tetramer peptide. Subsequently, it was compared in terms of changing antibacterial properties with another Sushi3 tetramer peptide the aspartic acid and proline amino acids of which were replaced with glycine and serine amino acids. Material & Methods: First, the mentioned Sushi3 tetramer peptide sequences were designed, constructed, and named Mer1 and Mer 2, respectively, and cloned separately into plasmid pET-26b (+) and finally transferred to E.coli BL21 host (DE3). After the expression of the peptides, the presence of peptides was confirmed by SDS-PAGE and Western blotting. Afterward, the antimicrobial activity of Mer1 and Mer 2 was evaluated and compared. Finally, the toxicity of the two tetramers made on the MDA-MB-231 cell line was evaluated and compared. Findings: Mer1 and Mer 2 had similar protein expression, and the toxic effect of both peptides on the cell line was not significantly different. however, Mer 2 had more effective antimicrobial effects than Mer1 at the same concentrations. Discussion & Conclusion: Evaluation of the effect of amino acid replacement with less negatively charge on increasing the antimicrobial activity of peptides is a suitable strategy. The above results increase the possibility of designing and producing antimicrobial peptides against antibiotic-resistant strains as the next generation of antibiotics.