The interaction of two cathelicidin antimicrobial peptides, LL-37 and SMAP-29, with three bacterial polysaccharides, respectively, produced
by Pseudomonas aeruginosa, Burkholderia cepacia and Klebsiella pneumoniae, was investigated to identify possible mechanisms adopted
by lung pathogens to escape the action of innate immunity effectors. In vitro assays indicated that the antibacterial activity of both peptides
was inhibited to a variable extent by the three polysaccharides. Circular dichroism experiments showed that these induced an -helical
conformation in the two peptides, with the polysaccharides from K. pneumoniae and B. cepacia showing, respectively, the highest and the
lowest effect. Fluorescence measurements also indicated the presence of peptide–polysaccharide interactions. A model is proposed in which
the binding of peptides to the polysaccharide molecules induces, at low polysaccharide to peptide ratios, a higher order of aggregation, due to
peptide–peptide interactions. Overall, these results suggest that binding of the peptides by the polysaccharides produced by lung pathogens
can contribute to the impairment of peptide-based innate defenses of airway surface.
