Conformation of a Bactericidal Domain of Puroindoline a: Structure and Mechanism of Action of a 13-Residue Antimicrobial Peptide

Abstract

Puroindoline a, a wheat endosperm-specific protein containing a tryptophan-rich domain, was reported to have antimicrobial activities. We found that a 13-residue fragment of puroindoline a (FPVTWRWWKWWK G-NH 2 ) (puroA) exhibits activity against both gram-positive and gram-negative bacteria. This suggests that puroA may be a bactericidal domain of puroindoline a. PuroA interacted strongly with negatively charged phospholipid vesicles and induced efficient dye release from these vesicles, suggesting that the microbicidal effect of puroA may be due to interactions with bacterial membranes. A variety of biophysical and biochemical methods, including fluorescence spectroscopy and microcalorimetry, were used to examine the mode of action of puroA. These studies showed that puroA is located at the membrane interface, probably due to its high content of Trp residues that have a high propensity to partition into the membrane interface. The penetration of these Trp residues in negatively charged phospholipid vesicles resembling bacterial membranes was more extensive than the penetration in neutral vesicles mimicking eukaryotic membranes. Peptide binding had a significant influence on the phase behavior of the former vesicles. The three-dimensional structure of micellebound puroA determined by two-dimensional nuclear magnetic resonance spectroscopy indicated that all the positively charged residues are oriented close to the face of Trp indole rings, forming energetically favorable cation-interactions. This characteristic, along with its well-defined amphipathic structure upon binding to membrane mimetic systems, allows puroA to insert more deeply into bacterial membranes and disrupt the regular membrane bilayer structure.

Antimicrobial Activity of Duck Egg Lysozyme against Salmonella enteritidis

“…The cationic charges of arginine provide an effective means of attracting with negative charged surfaces such as LPS, teichoic acid, or phosphatidyl glycerol phospholipids head group. Moreover, arginine can form a complex with tryptophans via cation-interaction which is favourable to penetrate into a lipid bilayer (Jing et al, 2003). The difference in arginine content may be responsible for high antimicrobial activity of dLz.…”

Inhibition of phospho-MurNAc-pentapeptide translocase (MraY) by nucleoside natural product antibiotics, bacteriophage ϕX174 lysis protein E, and cationic antibacterial peptides

“…Interestingly, the RWxxW motif found in the lysis protein E is also observed close to the N-or C-terminus of several naturally occurring cationic antimicrobial peptides, including indolicidin [51], cecropin [52], tritrpticin [53], lactoferricin B [54], and puroindoline A [55] as shown in Table 2. Many synthetic variants of cationic antimicrobial peptides have been generated by Hancock and co-workers, who have observed that Arg and Trp predominate in high activity peptide sequences [56][57][58], including that of clinical candidate MX226 (Omiganan) [57].…”

Cationic Antimicrobial Peptides

“…The preferential location of W residues at the membrane interface has been attributed to their aromaticity and ability to form hydrogen bonds with both water and polar lipid headgroup moieties [58,63,136,137,140,141]. In this study, hydrophobicity and highly membrane active -helical CAPs, were used for this purpose.…”

“…Furthermore, the influence of dipole and quadrupole moments became apparent in intramolecular interactions between the -electrons of the indole ring of W with the positively charged guanidino moiety of R in RW-rich peptides, which were suggested to stabilize the structure of CAPs and enhance membrane binding [136,137]. Because of the higher quadrupole moment (aromaticity) of the indole ring in c-(5MeoW)F(5MeoW) compared with c-(5fW)F(5fW) [124], a higher affinity of the former peptide for lipid bilayers was expected [136,137]. However, the opposite was observed ( Fig.…”