13-residue frog antimicrobial peptide Temporin L (TempL) possesses versatile antimicrobial activities and is considered as a lead molecule for the development of new antimicrobial agents. To find out the amino acid sequence(s) that influence the antimicrobial property of TempL, a phenylalanine zipper like sequence was identified in it which was not reported earlier. To evaluate the role of this motif, several alanine-substituted analogs and a scrambled peptide having the same composition of TempL were designed. To investigate if leucine residues instead of phenylalanine residues at 'a' and/or 'd' position(s) of the heptad repeat sequence could alter its antimicrobial property, several TempL-analogs were synthesized after substituting these phenylalanine residues with leucine residues. Substitution of phenylalanine with alanine residues in the phenylalanine zipper sequence significantly compromised the anti-endotoxin property of TempL. This is evident from the higher production of TNF-a and IL-6 in LPS-stimulated rat bone marrow derived macrophage cells in presence of its alanine-substituted analogs than TempL itself. However, substitution of these phenylalanine residues with leucine residues significantly augmented anti-endotoxin property of TempL. A single alanine substituted TempL-analog (F8A-TempL) showed significantly reduced cytotoxicity but retained the antibacterial activity of TempL while the two single leucine substituted analogs (F5L-TempL and F8L-TempL) though exhibited lower cytotoxicity, were able to retain the antibacterial activity of the parent peptide. The results demonstrated how minor amino acid substitutions in the identified phenylalanine zipper sequence in TempL could yield its analogs with better antibacterial and/or anti-endotoxin properties with their plausible mechanism of action.
- Temporin L
- anti-endotoxin activity of antimicrobial peptides
- Peptide-LPS interaction
- phenylalanine zipper sequence
- Fluorescence and circular dichroism studies
- synthetic peptides
- ©2016 The Author(s)
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