Identification, optimisation, and structure-activity relationship study of Caerin 1 peptides from the frog skin secretion of Litoria caerulea

The result indicates that the positive charge improvement on helix structure improve the antimicrobial activity and also influence the cytotoxicity. There are limitations to selective alteration by modifying the hinge motif. The hinge structure is unique structure in Caerin 1 family, the previous study has proved the important influence on antimicrobial activity.

In chapter 4, the modification strategy focus on the hinge structure to optimize the antimicrobial activity and cytotoxicity. The result indicates that the hydrophobicity of hinge motif dramatically influence cytotoxicity, Hence, Caerin 1.1-LC V(D)V(D) with D-form amino acid substitution on hinge motif greatly increased selectivity which indicates the modification strategy improve the selectivity of Caerin 1.1-LC to meet the clinical treatment requirement.

Due to the lack of general applicability of the independent sample modification strategy success, other samples were selected for hinge structure modification in chapter 5 to eliminate the contingency of modification strategy. Caerin 1.11 which was discovered from previous researcher study was optimized through hinge structure D-form amino acids substitution. After serial biological activity screens, Caerin 1.11 V(D)V(D) was identified as the acceptable antimicrobial agents with ideal antimicrobial activity and low cytotoxicity.

Caerin 1.11 V(D)V(D) meet the initial clinical requirement as antibiotic candidates and proved the feasibility of modification strategy of Caerin 1 family peptide for selectivity enhancement. The classical alpha helical structure AMPs has a low selectivity due to the membrane disruption mechanism. AMPs have to overcome the selectivity problem to meet the clinical treatment requirement.

In this thesis, the discovery of the novel antimicrobial peptide Caerin 1.1-LC from frog skin secretion and explore the modification strategy for better selectivity indicate further direction for the antimicrobial agents development. The unnatural amino acids substitution strategy on hinge structure has great improvement on the selectivity of Caeirn 1 family peptide and the modification provide a universal optimization strategy for antimicrobial peptides.

The exploration of the optimization strategy may contribute to the development of antibiotic candidates and the reduction of the probability of bacterial resistance.<br><br><i>Thesis is embargoed until 31 July 2030</i>.