Goldilocks Dilemma: LPS Works Both as the Initial Target and a Barrier for the Antimicrobial Action of Cationic AMPs on E. coli

Abstract

Antimicrobial peptides (AMPs) are generally membrane-active compounds that physically disrupt bacterial membranes. Despite extensive research, the precise mode of action of AMPs is still a topic of great debate. This work demonstrates that the initial interaction between the Gram-negative E. coli and AMPs is driven by lipopolysaccharides (LPS) that act as kinetic barriers for the binding of AMPs to the bacterial membrane. A combination of SPR and NMR experiments provide evidence suggesting that cationic AMPs first bind to the negatively charged LPS before reaching a binding place in the lipid bilayer. In the event that the initial LPS-binding is too strong (corresponding to a low dissociation rate), the cationic AMPs cannot effectively get from the LPS to the membrane, and their antimicrobial potency will thus be diminished. On the other hand, the AMPs must also be able to effectively interact with the membrane to exert its activity. The ability of the studied cyclic hexapeptides to bind LPS and to translocate into a lipid membrane is related to the nature of the cationic charge (arginine vs. lysine) and to the distribution of hydrophobicity along the molecule (alternating vs. clumped tryptophan).

Bacterial extracellular vesicles: towards realistic models for bacterial membranes in molecular interaction studies by surface plasmon resonance

“…The set was selected as a useful chemical model to study the effects of charge distribution on the interactions. The peptide c-LWwNKr ( Figure 5 ) was included in the study as a control that is chemically similar, but without antimicrobial activity (MIC > 256 μg/mL) ( Junkes et al, 2008 ; Bagheri, 2010 ; Gopal et al, 2012 ; Finger et al, 2015 ; Rainsford et al, 2022 ; Jakubec et al, 2023 ).…”

“…Antimicrobial peptides (AMPs) are receiving increasing attention in the fight against AMR, as their different mode of actions lead to destabilization of bacterial membranes and bacterial death ( Czaplewski et al, 2016 ; Mahlapuu et al, 2016 ; Ageitos et al, 2017 ; Kumar et al, 2018 ). A test panel of five cyclic AMPs with various distributions of charged and hydrophobic amino acids, known to interact with bacterial membranes was used ( Junkes et al, 2008 ; Bagheri, 2010 ; Gopal et al, 2012 ; Finger et al, 2015 ; Rainsford et al, 2022 ; Jakubec et al, 2023 ). This set of peptides was originally designed to study how the peptide charge distribution affects membrane interactions and was used by our lab to explore kinetics of binding towards synthetic liposomes, nanodiscs and to a series of E .…”

“…This set of peptides was originally designed to study how the peptide charge distribution affects membrane interactions and was used by our lab to explore kinetics of binding towards synthetic liposomes, nanodiscs and to a series of E . coli strains ( Rainsford et al, 2022 ; Jakubec et al, 2023 ).…”

LL-37: Structures, Antimicrobial Activity, and Influence on Amyloid-Related Diseases

“…Notably, three-dimensional structures of several AMPs are known to vary significantly when determined in cell membranes or membrane-mimicking environments [ 32 , 41 , 42 ]. In this regard, the atomic-resolution structures of several potent AMPs as a complex with an LPS outer membrane could be correlated with Gram-negative specific activity [ 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 ]. Cathelicidin-derived AMPs are found to be structurally diverse ( Table 2 ).…”

Preventing E. coli Biofilm Formation with Antimicrobial Peptide-Functionalized Surface Coatings: Recognizing the Dependence on the Bacterial Binding Mode Using Live-Cell Microscopy

“…Since AMPs lack an apparent secondary structure, the antibacterial mechanisms of short AMPs remain elusive but is more likely due to interference with membrane protein function than formation of pores. − Still, the efficacy and susceptibility profiles of short AMPs are very sensitive to minor alteration of the order and frequency at which amino acids appear ,, to peptide cyclization and to the position and stereochemistry of synthetic side-chains added to the pharmacophore . Given the wealth of possible combinations, exploring which molecular configuration is best for a certain application presents a real challenge.…”