EcDBS1R4, an Antimicrobial Peptide Effective against Escherichia coli with In Vitro Fusogenic Ability

Recent advances in the development of antimicrobial peptides against ESKAPE pathogens

Multi-drug resistant ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are a global health threat. The severity of the problem lies in its impact on mortality, therapeutic limitations, the threat to public health, and the costs associated with managing infections caused by these resistant strains. Effectively addressing this challenge requires innovative approaches to research, the development of new antimicrobials, and more responsible antibiotic use practices globally. Antimicrobial peptides (AMPs) are a part of the innate immune system of all higher organisms. They are short, cationic and amphipathic molecules with broad-spectrum activity. AMPs interact with the negatively charged bacterial membrane. In recent years, AMPs have attracted considerable interest as potential antibiotics. However, AMPs have low bioavailability and short half-lives, which may be circumvented by chemical modification. This review presents recent in vitro and in silico strategies for the modification of AMPs to improve their stability and application in preclinical experiments.

Expression of the Antimicrobial Peptide SE-33-A2P, a Modified Analog of Cathelicidin, and an Analysis of Its Properties

In this study, we developed a method for the expression of the antimicrobial peptide SE-33-A2P in E. coli bacterial cells. The SE-33-A2P peptide consists of A2P and SE-33 peptides and is a retro analog of cathelicidin possessing antimicrobial activity against both Gram-positive and Gram-negative bacteria. Furthermore, the A2P peptide is a self-cleaving peptide. For an efficient expression of the SE-33-A2P peptide, a gene encoding several repetitive sequences of the SE-33 peptide separated by A2P sequences was created. The gene was cloned into a plasmid, with which E. coli cells were transformed. An induction of the product expression was carried out by IPTG after the cell culture gained high density. The inducible expression product, due to the properties of the A2P peptide, was cleaved in the cell into SE-33-A2P peptides. As the next step, the SE-33-A2P peptide was purified using filtration and chromatography. Its activity against both Gram-positive and Gram-negative bacteria, including antibiotic-resistant bacteria, was proved. The developed approach for obtaining a prokaryotic system for the expression of a highly active antimicrobial peptide expands the opportunities for producing antimicrobial peptides via industrial methods.

Bacterial susceptibility and resistance to modelin-5

Modelin-5 (M5-NH2) killed Pseudomonas aeruginosa with a minimum lethal concentration (MLC) of 5.86 μM and strongly bound its cytoplasmic membrane (CM) with a Kd of 23.5 μM. The peptide adopted high levels of amphiphilic α-helical structure (75.0%) and penetrated the CM hydrophobic core (8.0 mN m-1). This insertion destabilised CM structure via increased lipid packing and decreased fluidity (ΔGmix < 0), which promoted high levels of lysis (84.1%) and P. aeruginosa cell death. M5-NH2 showed a very strong affinity (Kd = 3.5 μM) and very high levels of amphiphilic α-helical structure with cardiolipin membranes (96.0%,) which primarily drove the peptide's membranolytic action against P. aeruginosa. In contrast, M5-NH2 killed Staphylococcus aureus with an MLC of 147.6 μM and weakly bound its CM with a Kd of 117.6 μM, The peptide adopted low levels of amphiphilic α-helical structure (35.0%) and only penetrated the upper regions of the CM (3.3 mN m-1). This insertion stabilised CM structure via decreased lipid packing and increased fluidity (ΔGmix > 0) and promoted only low levels of lysis (24.3%). The insertion and lysis of the S. aureus CM by M5-NH2 showed a strong negative correlation with its lysyl phosphatidylglycerol (Lys-PG) content (R2 > 0.98). In combination, these data suggested that Lys-PG mediated mechanisms inhibited the membranolytic action of M5-NH2 against S. aureus, thereby rendering the organism resistant to the peptide. These results are discussed in relation to structure/function relationships of M5-NH2 and CM lipids that underpin bacterial susceptibility and resistance to the peptide.

Activity modulation of the Escherichia coli F1FO ATP synthase by a designed antimicrobial peptide via cardiolipin sequestering

Most antimicrobial peptides (AMPs) exert their microbicidal activity through membrane permeabilization. The designed AMP EcDBS1R4 has a cryptic mechanism of action involving the membrane hyperpolarization of Escherichia coli, suggesting that EcDBS1R4 may hinder processes involved in membrane potential dissipation. We show that EcDBS1R4 can sequester cardiolipin, a phospholipid that interacts with several respiratory complexes of E. coli. Among these, F₁F_O ATP synthase uses membrane potential to fuel ATP synthesis. We found that EcDBS1R4 can modulate the activity of ATP synthase upon partition to membranes containing cardiolipin. Molecular dynamics simulations suggest that EcDBS1R4 alters the membrane environment of the transmembrane F_O motor, impairing cardiolipin interactions with the cytoplasmic face of the peripheral stalk that binds the catalytic F₁ domain to the F_O domain. The proposed mechanism of action, targeting membrane protein function through lipid reorganization may open new venues of research on the mode of action and design of other AMPs.

Creation of New Antimicrobial Peptides

Antimicrobial peptides (AMPs) are natural compounds that exhibit potent antimicrobial activity against various microorganisms, including bacteria, fungi, and viruses [...].

Efficacy of natural antimicrobial peptides versus peptidomimetic analogues: a systematic review

Aims: This systematic review was carried out to determine whether synthetic peptidomimetics exhibit significant advantages over antimicrobial peptides in terms of in vitro potency. Structural features - molecular weight, charge and length - were examined for correlations with activity. Methods: Original research articles reporting minimum inhibitory concentration  values against Escherichia coli, indexed until 31 December 2020, were searched in PubMed/ScienceDirect/Google Scholar and evaluated using mixed-effects models. Results: In vitro antimicrobial activity of peptidomimetics resembled that of antimicrobial peptides. Net charge significantly affected minimum inhibitory concentration values (p < 0.001) with a trend of 4.6% decrease for increments in charge by +1. Conclusion: AMPs and antibacterial peptidomimetics exhibit similar potencies, providing an opportunity to exploit the advantageous stability and bioavailability typically associated with peptidomimetics.

Leaky membrane fusion: an ambivalent effect induced by antimicrobial polycations

Both antimicrobial peptides and their synthetic mimics are potential alternatives to classical antibiotics. They can induce several membrane perturbations including permeabilization. Especially in model studies, aggregation of vesicles by such polycations is often reported. Here, we show that unintended vesicle aggregation or indeed fusion can cause apparent leakage in model studies that is not possible in most microbes, thus potentially leading to misinterpretations. The interactions of a highly charged and highly selective membrane-active polycation with negatively charged phosphatidylethanolamine/phosphatidylglycerol (PE/PG) vesicles are studied by a combination of biophysical methods. At low polycation concentrations, apparent vesicle aggregation was found to involve exchange of lipids. Upon neutralization of the negatively charged vesicles by the polycation, full fusion and leakage occurred and leaky fusion is suspected. To elucidate the interplay of leakage and fusion, we prevented membrane contacts by decorating the vesicles with PEG-chains. This inhibited fusion and also leakage activity. Leaky fusion is further corroborated by increased leakage with increasing likeliness of vesicle-vesicle contacts. Because of its similar appearance to other leakage mechanisms, leaky fusion is difficult to identify and might be overlooked and more common amongst polycationic membrane-active compounds. Regarding biological activity, leaky fusion needs to be carefully distinguished from other membrane permeabilization mechanisms, as it may be less relevant to bacteria, but potentially relevant for fungi. Furthermore, leaky fusion is an interesting effect that could help in endosomal escape for drug delivery. A comprehensive step-by-step protocol for membrane permeabilization/vesicle leakage using calcein fluorescence lifetime is provided in the ESI.

Beta-lactam resistance and the effectiveness of antimicrobial peptides against KPC-producing bacteria

Bacterial resistance is a problem that is giving serious cause for concern because bacterial strains such as Acinetobacter baumannii and Pseudomonas aeruginosa are difficult to treat and highly opportunistic. These bacteria easily acquire resistance genes even from other species, which confers greater persistence and tolerance towards conventional antibiotics. These bacteria have the highest death rate in hospitalized intensive care patients, so strong measures must be taken. In this review, we focus on the use of antimicrobial peptides (AMPs) as an alternative to traditional drugs, due to their rapid action and lower risk of generating resistance by microorganisms. We also present an overview of beta-lactams and explicitly explain the activity of AMPs against carbapenemase-producing bacteria as potential alternative agents for infection control.

Interplay of Fusion, Leakage, and Electrostatic Lipid Clustering: Membrane Perturbations by a Hydrophobic Antimicrobial Polycation

Membrane active compounds are able to induce various types of membrane perturbations. Natural or biomimetic candidates for antimicrobial treatment or drug delivery scenarios are mostly designed and tested for their ability to induce membrane permeabilization, also termed leakage. Furthermore, the interaction of these usually cationic amphiphiles with negatively charged vesicles often causes colloidal instability leading to vesicle aggregation or/and vesicle fusion. We show the interplay of these modes of membrane perturbation in mixed phosphatidyl glycerol (PG)/phosphatidyl ethanolamine (PE) by the statistical copolymer MM:CO comprising, both, charged and hydrophobic subunits. MM:CO is a representative of partially hydrophobic, highly active, but less selective antimicrobial polycations. Cryo-electron microscopy indicates vesicle fusion rather than vesicle aggregation upon the addition of MM:CO to negatively charged PG/PE (1:1) vesicles. In a combination of fluorescence-based leakage and fusion assays, there is support for membrane permeabilization and pronounced vesicle fusion activity as distinct effects. To this end, membrane fusion and aggregation were prevented by including lipids with polyethylene glycol attached to their head groups (PEG-lipids). The leakage activity of MM:CO is very similar in the absence and presence of PEG-lipids. Vesicle aggregation and fusion however are largely suppressed. This strongly suggests that MM:CO induces leakage by asymmetric packing stress because of hydrophobically driven interactions which could lead to leakage. As a further membrane perturbation effect, MM:CO causes lipid clustering in model vesicles. We address potential artifacts and misinterpretations of experiments characterizing leakage and fusion. Additional to the leakage activity, the pronounced fusogenic activity of the polymer and potentially of many other similar compounds likely has implications for antimicrobial activity and beyond.