Journal
BIOCHEMISTRY
Volume 41, Issue 7, Pages 2254-2263Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi011549t
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Our basic understanding of how to combat fungal infections has not kept pace with the recent sharp rise in life-threatening cases found particularly among immuno-compromised individuals. Current investigations for new potential antifungal agents have focused on anti microbial peptides. which are used as a cell-free defense mechanism in all organisms. Unfortunately, despite their high antibacterial activity, most of them are not active toward fungi, the reason of which is not clear. Here, we present a new approach to modify an antibacterial peptide, a magainin analogue, to display antifungal activity by its conjugation with lipophilic acids. This approach has the advantage of producing well-defined changes in hydrophobicity, secondary structure, and self-association. These modifications were characterized in solution at physiological concentrations using CD spectroscopy, tryptophan fluorescence, and analytical ultracentrifugation. In order of increasing hydrophobicity, the attachment to the magainin-2 analogue of (i) heptanoic acid results in a monomeric, unordered structure, (ii) undecanoic acid yields concentration-dependent oligomers of alpha helices, and (iii) palmitic acid yields concentration-independent alpha-helical monomers, a novel lipopeptide structure, which is resistant to proteolytic digestion. Membrane-lipopeptide interactions and the membrane-bound structures were studied using fluorescence and ATR-FTIR in PC/PE/PI/ergosterol (5/2.5/2.5/1, w/w) SUV, which constitute the major components of Candida albicans bilayers. A direct correlation was found between oligomerization of the lipopeptides in solution and potent antifungal activity. These results provide insight to a new approach of modulating hydrophobicity and self-assembly of antimicrobial peptides in solution, without altering the sequence of the peptidic chain, These studies also provide a general means of developing a new group of lipopeptide candidates as therapeutic agents against fungal infections.
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