Characterization and performance of short cationic antimicrobial peptide isomers

Abstract

Cationic antimicrobial peptides (CAMPs) represent an ancient defense mechanism against invading bacteria, with peptides such as the cathelicidins being essential elements of vertebrate innate immunity. CAMPs are typically associated with broad-spectrum antimicrobial potency and limited bacterial resistance. The cathelicidin identified from the elapid snake Naja atra (NA-CATH) contains a semi-conserved repeated 11-residue motif (ATRA motif) with a sequence pattern consistent with formation of an amphipathic helical conformation. Short peptide amides (ATRA-1, -1A, -1P, and -2) generated based on the pair of ATRA motifs in NA-CATH exhibited varied antimicrobial potencies. The small size of the ATRA peptides, coupled with their varied antimicrobial performances, make them interesting models to study the impact various physico-chemical properties have on antimicrobial performance in helical CAMPs. Accordingly, the D- and L-enantiomers of the peptide ATRA-1A, which in earlier studies had shown both good antimicrobial performance and strong helical character, were investigated in order to assess the impact peptide stereochemistry has on antimicrobial performance and interaction with chiral membranes. The ATRA-1A isomers exhibit varied potencies against four bacterial strains, and their conformational properties in the presence of mixed zwitterionic/anionic liposomes are influenced by anionic lipid content. These studies reveal subtle differences in the properties of the peptide isomers. Differences are also seen in the abilities of the ATRA-1A isomers to induce liposome fusion/aggregation, bilayer rearrangement and lysing through turbidity studies and fluorescence microscopy. The similarities and differences in the properties of the ATRA-1A isomers could aid in efforts to develop D-peptide-based therapeutics using high-performing L-peptides as templates.

The structure and behavior of the NA-CATH antimicrobial peptide with liposomes

“…Residues Val27 to Thr31 are predicted to adopt an extended structure. Previously, circular dichroism data have indicated that the peptide and the shorter ATRA-1A construct adopt a stable helical conformation in 50% TFE [19,46].…”

“…Given that the peptide has been observed interacting with membranes [19,44,46,49], we next have investigated whether the peptide would adopt a stable structure in the presence of 80:20 DOPC:DOPG liposomes, which serve as a mimic of the bacterial membranes (Fig. 1B).…”

“…Previous studies reveal a semi-conserved 11 amino-acid (KRAKKFFKKLK-NH 2 ) motif, ATRA-1A, that has antimicrobial activity on its own, similar to the full length peptide [19]. This motif appears twice within the sequence, with only a few differences in the nonbasic amino acids.…”

Melittin peptides exhibit different activity on different cells and model membranes

“…Although the mechanism of AMP action is unknown and pore formation in cell membranes may be responsible for lytic ability, it is well established that AMP interact directly with the cell membrane surface and are able to enter the lipid bilayer, resulting in cell membrane disruption and leakage of cytoplasmic components which leads to killing of microbes (Lee et al 2010;Izadpanah and Gallo 2005;Lorenzon et al 2012;Sani et al 2013). AMP have attracted much attention as an alternative to antibiotics because of their effect against bacterial infections and drug resistant bacteria (Juba et al 2013;AnayaLopez et al 2013).…”

Vipericidins, Snake Venom Cathelicidin-Related Peptides, in the Milieu of Reptilian Antimicrobial Polypeptides

“…For example, de Latour and coworkers (2010) produced a series of very short peptides that were derived from the Naja atra cathelicidin, containing the so-called ATRAmotif [KR(F/A)KKFFKK(L/P)K], and demonstrated their low toxicity to host cells and high-potent antimicrobial activity against Gram-negative bacteria. The efficacy test of short d-enantiomer peptides that were derived from ATRA-motif indicates that these isomeric peptides exhibit varied potencies against bacterial strains and that helicity propensity (conformational helix) depends on the anionic content of the membranes (Juba et al 2013). The modulation of the structure and function of snake venom cathelicidin can also be ascertained by BF-15, a 15-mer peptide that was derived from cathelicidin-BF (BF-30) and that maintains an amphipathic a-helix and potent antimicrobial activity against antibiotic-resistant bacteria but exhibits reduced hemolytic activity (Chen et al 2011b).…”