Design of new truncated derivatives based on direct and reverse mirror repeats of first six residues of Caerin 4 antimicrobial peptide and evaluation of their activity and cytotoxicity.

Caerin 4 is a family of AMPs isolated from the frog called Litoria caerulea. In silico drug designing methods and using machine learning algorithms for AMPs design can reduce their usage restrictions such as production costs and the time required for investigation of their activity and toxicity. In this study, two short peptides were designed based on direct and reverse mirror repeats of GLWQKI conserved sequence from Caerin 4 family that called dCar12 and rCar12. Also, Caerin 4.1 was synthesized without primary GLWQKI sequence and named Car . Following the synthesis of peptides, their antimicrobial properties, cytotoxicity, secondary structure, and mode of action were further evaluated. Results indicated that rCar12 had a good antibacterial activity (at an MIC of 3.9-62.5 µg/ml), while Car did not have any antimicrobial properties. Cytotoxicity of rCar12 at MICs range was <5%, which is much less than Caerin 4.1. In conclusion, rCar12 with reverse mirror repeat has different functional properties compared with dCar12. These results corroborate the fact that in two peptides with identical residues and length, the position and arrangement of amino acids are very important concerning peptide function. Moreover, GLWQKI sequence is highly crucial for the antimicrobial activity of Caerin 4 antimicrobial peptide family.