Effect of Fluorination on Membrane Interactions of an Antimicrobial Peptoid Macrocycle

Abstract

Antimicrobial peptides (AMPs) are important components of the innate immune system of animals and plants. AMPs are considered promising alternatives to conventional antibiotic treatments, as they exhibit a broad spectrum activity [1]. Understanding the mechanism by which AMPs interact with membranes is fundamental for explaining their biological action. We present a study of two synthetic peptides: Gm1, a cecropine neutral D-like peptide, from Galleria mellonella with activity against Gram-positive, Gram-negative bacteria and fungi [2], and DGm1, a modified structure of Gm1. The aim of the modification was to evaluate the biological activity that increases the cationic amino acids. We have studied the interaction of peptides by applying Fourier-transform infrared spectroscopy (FTIR) and Föster resonance energy transfer spectroscopy (FRET), using pholipid membranes built-up lipopolysaccharide (LPS) and dimyristoylphosphatidylglycerol (DMPG) as representative components of the outer and cytoplasmic bacterial membrane, respectively. Atomic force microscopy (AFM) was used to evaluate the effect of the peptides on the bacterial cells of P. mirabilis R45, and colony counting assay was employed to evaluate the antimicrobial activity. FTIR results showed an opposite effect on the acyl chain packing of lipids. FRET experiments confirmed the incorporation of peptides into the lipid membranes. Considerable alterations were observed in the morphology of P. mirabilis R45. The exposure of the bacteria to Gm1 leads to grooves and when exposed to DGm1, it induces the formation of indentations and cell debris in P. mirabilis R45. The colony counting assay showed that DGm1 also has biological activity. [1] K.L. Brown, R.E. Hancock, Cationic host defense (antimicrobial) peptides,