Structural contributions to the intracellular targeting strategies of antimicrobial peptides

Abstract

The interactions of cationic amphipathic antimicrobial peptides (AMPs) with anionic biological membranes have been the focus of much research aimed at improving the activity of such compounds in the search for therapeutic leads. However, many of these peptides are thought to have other polyanions, such as DNA or RNA, as their ultimate target. Here a combination of fluorescence and circular dichroism (CD) spectroscopies has been used to assess the structural properties of amidated versions of buforin II, pleurocidin and magainin 2 that support their varying abilities to translocate through bacterial membranes and bind to double stranded DNA. Unlike magainin 2 amide, a prototypical membrane disruptive AMP, buforin II amide adopts a poorly helical structure in membranes closely mimicking the composition of Gram negative bacteria, such as Escherichia coli, and binds to a short duplex DNA sequence with high affinity, ultimately forming peptide-DNA condensates. The binding affinities of the peptides to duplex DNA are shown to be related to the structural changes that they induce. Furthermore, CD also reveals the conformation of the bound peptide buforin II amide. In contrast with a synthetic peptide, designed to adopt a perfect amphipathic alpha-helix, buforin II amide adopts an extended or polyproline II conformation when bound to DNA. These results show that an alpha-helix structure is not required for the DNA binding and condensation activity of buforin II amide.

Combined Systems Approaches Reveal Highly Plastic Responses to Antimicrobial Peptide Challenge in Escherichia coli

“…We have recently solved the high resolution structures of both magainin 2 and pleurocidin in the anionic detergent SDS (PDB entries 2LSA and 2LS9 respectively) and found similar regions of flexibility around the glycine residues in the middle section of the sequence (Gly 13/18 – magainin 2; Gly 13/17 – pleurocidin). Only in the membranes that most closely mimic the inner membrane of Gram-negative bacteria are any differences between the two peptides observed; here pleurocidin adopts a notably more disordered conformation under these conditions [18]. The more disordered conformation of pleurocidin in the E. coli target membrane may be related to possible pore formation [39] or the proposed intracellular targeting strategy [22] which, in both cases, would serve to boost its potency.…”

Cationic amphipathic peptides KT2 and RT2 are taken up into bacterial cells and kill planktonic and biofilm bacteria

“…Pep-384 tide KT2 had the strongest ability to bind to DNA at a 1:1 DNA:peptide 385 weight ratio, which was substantially higher than that previously re- Interaction of peptide tryptophan residues with the hydrophobic core of liposomes. This in the previous studies [10], the helical content of these peptides seems 394 not important for their antibacterial mechanism, which is the same as 395 buforin II, while the helical content is a distinct characteristics of mem-396 brane active peptides such as magainin II [32]. Caixa" and Fundación Canadá (Spain).…”

“…8), since the electrostatic interactions between the 377 positive charges of the peptides, which are burying in the lipid core 378 (Table 1), and the negative charge of DNA might lead the peptides to ac-379 cumulate within bacterial cells and also provide a potential mechanism 380 of action [3]. Magainin II, which has poor DNA-binding ability [8,32], 381 was used as a negative control (Fig. 8).…”

Pseudomonas aeruginosa Psl Exopolysaccharide Interacts with the Antimicrobial Peptide LG21

“…AMPs are amphipathic molecules that can directly interact with bacterial cell wall components such as lipopolysaccharide (LPS) and compromise the cell wall integrity [2]. AMPs are also able to target microbial intracellular components such as DNA and RNA [3]. In addition to directly targeting microbial cells, host-derived AMPs are known to modulate the innate immune response and boost the host's capacity for bacterial clearance [4].…”