Recombinant Tandem Repeated Expression of S3 and S∆3 Antimicrobial Peptides

Background: Antimicrobial peptides (AMPs) are promising candidates for new generations of antibiotics to overcome the threats of multidrug-resistant infections as well as other industrial applications. Recombinant expression of small peptides is challenging due to low expression rates and high sensitivity to proteases. However, recombinant multimeric or fusion expression of AMPs facilitates cost-effective large-scale production of AMPs. In This project, S3 and S∆3 AMPs were expressed as fusion partners. S3 peptide is a 34 amino acid linear antimicrobial peptide derived from lipopolysaccharide (LPS) binding site of factor C of horseshoe crab hemolymph and S∆3 is a modified variant of S3 possessing more positive charges. Methods: Two copy tandem repeat of the fusion protein (named as S∆3S3-2mer-GS using glycine- serine linker was expressed in E. coli. BL21 (DE3). After cell disruption and solubilization of inclusion bodies, the protein was purified by Ni -NTA affinity chromatography. Antimicrobial activity and cytotoxic properties of purified S∆3S3-2mer-GS were compared with a previously produced tetramer of S3 with the same glycine- serine linker (S3-4mer-GS) and each of monomeric blocks of S3 and S∆3. Results: S∆3S3-2mer-GS was successfully expressed with an expression rate of 26%. The geometric average of minimum inhibitory concentration (MIC GM) of S∆3S3-2mer-GS was 28%, 34%, and 57% lower than S∆3, S3-4mer-GS, and S3, respectively. S∆3S3-2mer-GS had no toxic effect on eukaryotes human embryonic kidney cells at its MIC concentration. Conclusions: tandem repeated fusion expression strategy could be employed as an effective technique for recombinant production of AMPs.