| In this study, we report the synthesis of a potent antimicrobial peptide Leucocin A (LeuA) using two solid phase peptide synthesis methods. One of the methods, native chemical ligation, gave high yield (12.5%) of 37-residue LeuA and can be utilized in the synthesis of LeuA to perform structure-activity relationship (SAR) studies. Three analogues (1-3) of LeuA were designed and synthesized to explore the SAR in the N-terminal domain of LeuA. In the analogues, N-terminal β-sheet residues Cys9-Ser15 of the native peptide were replaced with shorter β-turn motifs. Such replacement abolished the antimicrobial activity in all the analogues. Circular dichroism spectroscopy suggested that only analogue 1 adopted similar folding as LeuA. Therefore, 1 was able to competitively inhibit the activity of native LeuA. However, analysis of the secondary structure of 1 using molecular dynamics simulations suggested lack of β-sheet formation in the N-terminal region compared to LeuA emphasizing the role of proper folding and sequence in the activity of class IIa bacteriocins. |
