Structural and DNA-binding studies on the bovine antimicrobial peptide, indolicidin: evidence for multiple conformations involved in binding to membranes and DNA

Abstract

Indolicidin, a l3-residue antimicrobial peptide-amide, which is unusually rich in tryptophan and proline, is isolated from the cytoplasmic granules of bovine neutrophils. In this study, the structures of indolicidin in 50% D3-trifluoroethanol and in the absence and presence of SDS and D38-dodecylphosphocholine were determined using NMR spectroscopy. Multiple conformations were found and were shown to be due to different combinations of contact between the two WPW motifs. Although indolicidin is bactericidal and able to permeabilize bacterial membranes, it does not lead to cell wall lysis, showing that there is more than one mechanism of antimicrobial action. The structure of indolicidin in aqueous solution was a globular and amphipathic conformation, differing from the wedge shape adopted in lipid micelles, and these two structures were predicted to have different functions. Indolicidin, which is known to inhibit DNA synthesis and induce filamentation of bacteria, was shown to bind DNA in gel retardation and fluorescence quenching experiments. Further investigations using surface plasmon resonance confirmed the DNA-binding ability and showed the sequence preference of indolicidin. Based on our biophysical studies and previous results, we present a diagram illustrating the DNA-binding mechanism of the antimicrobial action of indolicidin and explaining the roles of the peptide when interacting with lipid bilayers at different concentrations.

Antimicrobial peptides as new recognition molecules for screening challenging species

“…AMPs comprise part of the innate immune system of many organisms and help protect the host species from microbial invasion/infection. Current dogma dictates that the antimicrobial activity of these peptides is mediated through interaction of AMPs with target cell membranes and subsequent membrane disruption, although other mechanisms have been postulated [12][13][14]. The current study expands on previous work developing AMP-based detection assays for Escherichia coli and Salmonella typhimurium [15,16].…”

Investigation into the mechanism of action of the antimicrobial peptides Os and Os-C derived from a tick defensin

“…Buforin II was previously found to bind pDNA at a weight ratio of above 1:0.25 (pDNA:peptide) [23]. Another AMP, indolicidin, has been shown to cause membrane permeabilization without cell lysis, and to have possible intracellular targets through which it kills bacteria [13]. Indolicidin retards the movement of DNA at pDNA:peptide ratios of above 1:0.2 [13].…”

“…Another AMP, indolicidin, has been shown to cause membrane permeabilization without cell lysis, and to have possible intracellular targets through which it kills bacteria [13]. Indolicidin retards the movement of DNA at pDNA:peptide ratios of above 1:0.2 [13]. The peptides Os and Os-C cause pDNA retardation at weight ratios above 1:1.2 and 1:1 (pDNA:peptide), respectively.…”

Cationic Peptide Interactions with Biological Macromolecules

“…The actual contact between an AMP and DNA was demonstrated with indolicidin, a potent cationic peptide that enters bacterial cells without causing lysis and inhibits DNA replication [61]. These experiments showed that indolicidin assumes different environmentdependent conformations and prefers to bind certain sequences of double stranded DNA and that it binds poorly to single stranded DNA .…”