Hydrophobic Interactions in Complexes of Antimicrobial Peptides with Bacterial Polysaccharides

Abstract

Biofilms of Pseudomonas aeruginosa are responsible for chronic lung infections in cystic fibrosis patients, where they are characterized by overproduction of the exopolysaccharide alginate and are recalcitrant to treatment with conventional antibiotics. Cationic antimicrobial peptides (CAPs) are potential alternatives for the treatment of multi-drug-resistant P. aeruginosa. However, alginate in P. aeruginosa biofilms has been proposed to bind these peptides through hydrophobic interactions, consequently reducing their activity [Chan et al., J Biol Chem 2004; 279: 38749-38754]. Here we perform biophysical analyses of the interactions of alginate with a series of novel peptide antibiotics (alpha-CAPs) of prototypic sequence KK-AAAXAAAAAXAAWAAXAAA-KKKK (where X = Phe, Trp or Leu). The hydrophobic interaction interface in alginate was investigated by examining (i) the effects of polysaccharide composition with respect to D-mannuronate and L-guluronate content; (ii) glycan chain length; (iii) alpha-CAP Trp fluorescence; and (iv) 1-anilinonaphthalene-8-sulfonate fluorescence. The results show that, while M and G residues produce equivalent effects, hydrophobic interactions between alginate and alpha-CAPs require a minimal glycan chain length. Peptide interactions with alginate are deduced to be mediated by hydrophobic microdomains comprised of pyranosyl C-H groups that are inducible upon formation of alpha-CAP-alginate complexes due to charge neutralization between the two species.

The impact of membrane lipid composition on antimicrobial function of an α-helical peptide

“…These higher levels of resistance may be explained in part by the presence of exopolysaccharides (EPS) in the extracellular matrix of bacterial biofilms. It has been shown that EPS possess structural properties mimetic of bacterial membranes, enabling them to bind -AMPs with mean hydrophobicity above a threshold of 0.4 as measured using the Liu-Deber hydrophobicity scale, effectively increasing the level of peptide required for biofilm killing (Chan et al, 2004;Kuo et al, 2007).…”

The particle in the spider's web: transport through biological hydrogels

“…116–118 For example, the Deber group designed a set of synthetic anti- P. aeruginosa CAMPs and investigated their interaction with alginate. 119–122 While alginate is anionic, highly soluble, and contains no large hydrophobic domains, alginate blocked the penetration of synthetic anti- P. aeruginosa CAMPs when a hydrophobicity threshold was exceeded. 121 Furthermore, they showed that this interaction was mediated by a combination of electrostatic and hydrophobic interactions with alginate.…”

Interactions between bovine serum albumin and alginate: An evaluation of alginate as protein carrier

“…Ionic bindings were believed to be responsible for Ca-alginate gel formation and emulsification of protein-alginate mixtures. Researchers further identified that alginate is capable of mediating hydrophobic interactions with certain cationic peptides despite the lack of obvious hydrophobic functional groups in such a water-soluble polysaccharide [12]. Although studies have been devoted to understand the protein-polysaccharide system, previous researchers have mainly focused on the effect of intermolecular interactions on the thermal gelation properties of polysaccharides at different pH and ionic strengths [13][14][15].…”