Editorial: Natural Antimicrobial Peptides: Hope for New Antibiotic Lead Molecules

Antibacterial and Anti-Inflammatory Activity of Branched Peptides Derived from Natural Host Defense Sequences

Antibiotic resistance is a major global health threat, necessitating the development of new treatments and diverse molecules to combat severe infections and preserve the efficacy of existing drugs. Antimicrobial peptides (AMPs) offer a versatile arsenal against bacteria, and peptide structure branching can enhance their resistance to proteases and improve their overall efficacy. A small library of peptides derived from natural host defense peptides and synthesized in a tetrabranched form was selected against E. coli. Six selected branched peptides were further studied for antibacterial activity against a panel of strains, biofilm inhibition, protease resistance, and cytotoxicity. Their structure was predicted computationally and their mechanism of action was investigated by electron microscopy and by using fluorescent dyes. The peptide BAMP2 showed promise in a mouse skin infection model, indicating the potential for local infection treatment.

A novel antimicrobial peptide S24 combats serious wound infections caused by Pseudomonas aeruginosa and Acinetobacter baumannii

OBJECTIVES

Pseudomonas aeruginosa and Acinetobacter baumannii are ranked as top-priority organisms by WHO. Antimicrobial peptides (AMPs) are promising antimicrobial agents that are highly effective against serious bacterial infections.

METHODS

In our previous study, a series of α-helical AMPs were screened using a novel multiple-descriptor strategy. The current research suggested that S24 exhibited strong antimicrobial activity against major pathogenic bacteria, and displayed minimal haemolysis, good serum stability and maintained salt resistance.

RESULTS

We found that S24 exerted an antimicrobial effect by destroying outer membrane permeability and producing a strong binding effect on bacterial genomic DNA that inhibits genomic DNA migration. Furthermore, S24 exerted a strong ability to promote healing in wound infected by P. aeruginosa, A. baumannii and mixed strains in a mouse model.

CONCLUSIONS

Overall, S24 showed good stability under physiological conditions and excellent antimicrobial activity, suggesting it may be a potential candidate for the development of serious bacterial infection treatment.

Characterization of an antimicrobial peptide family from the venom gland of Heteropoda venatoria

Spider venom boasts extensive peptide diversity, constituting a natural biochemical arsenal for defense and predation. The new family HvAMPs, including 9 homologous members, were identified from the unnormalized cDNA library of Heteropoda venatoria venom gland by Sanger sequencing. The putative mature peptide is composed of 22 aliphatic amino acid residues. The mature peptides of HvAMP1 and HvAMP5, with 3 different amino acids, were synthesized and both were shown to adopt an amphipathic α-helical structure and amphipathicity in SDS buffer by CD spectroscopy. In comparison to HvAMP1, HvAMP5 exhibits higher antibacterial activity, particularly against Gram-positive bacteria, coupled with reduced hemolytic activity and cytotoxicity. Results from SYTO 9/PI staining indicate that HvAMP5 acts by disrupting bacterial cell membranes. Analysis of the relationships between structures and functions suggests that HvAMP5 enhances antibacterial activity and reduces mammalian cell toxicity by increasing positive charge and proline substitution. The three residues variation can augment the electrostatic attraction of antibacterial peptides to the bacterial phospholipid bilayer. The present study suggests that the HvAMPs may exert lytic action against cells of different origins to increase cellular and tissue barrier permeability to facilitate spider's defense or predation. Moreover, HvAMP5 holds promise as a novel antibacterial agent for treating Gram-positive bacterial infections. Simultaneously, the numerous diverse amino acid residue substitutions within the HvAMP family offer a template for future study.

Diversity of Antimicrobial Peptides in Silkworm

Antimicrobial resistance is a phenomenon that the present-day world is witnessing that poses a serious threat to global health. The decline in the development of novel therapeutics over the last couple of decades has exacerbated the situation further. In this scenario, the pursuit of new alternative therapeutics to commonly used antibiotics has gained predominance amongst researchers across the world. Antimicrobial peptides (AMPs) from natural sources have drawn significant interest in the recent years as promising pharmacological substitutes over the conventional antibiotics. The most notable advantage of AMPs is that microorganisms cannot develop resistance to them. Insects represent one of the potential sources of AMPs, which are synthesized as part of an innate immune defence against invading pathogens. AMPs from different insects have been extensively studied, and silkworm is one of them. Diverse classes of AMPs (including attacins, cecropins, defensins, enbocins, gloverins, lebocins and moricins) were identified from silkworm that exhibit antimicrobial property against bacteria, fungi and viruses, indicating their potential therapeutic benefits. This review briefs about the immune responses of silkworm to invading pathogens, the isolation of AMPs from silkworms, AMPs reported in silkworms and their activity against various microorganisms.

Real-Time Fluorescence Microscopy on Living E. coli Sheds New Light on the Antibacterial Effects of the King Penguin β-Defensin AvBD103b

(1) Antimicrobial peptides (AMPs) are a promising alternative to conventional antibiotics. Among AMPs, the disulfide-rich β-defensin AvBD103b, whose antibacterial activities are not inhibited by salts contrary to most other β-defensins, is particularly appealing. Information about the mechanisms of action is mandatory for the development and approval of new drugs. However, data for non-membrane-disruptive AMPs such as β-defensins are scarce, thus they still remain poorly understood. (2) We used single-cell fluorescence imaging to monitor the effects of a β-defensin (namely AvBD103b) in real time, on living E. coli, and at the physiological concentration of salts. (3) We obtained key parameters to dissect the mechanism of action. The cascade of events, inferred from our precise timing of membrane permeabilization effects, associated with the timing of bacterial growth arrest, differs significantly from the other antimicrobial compounds that we previously studied in the same physiological conditions. Moreover, the AvBD103b mechanism does not involve significant stereo-selective interaction with any chiral partner, at any step of the process. (4) The results are consistent with the suggestion that after penetrating the outer membrane and the cytoplasmic membrane, AvBD103b interacts non-specifically with a variety of polyanionic targets, leading indirectly to cell death.

SuPepMem: a database of innate immune system peptides and their cell membrane interactions

Host defense peptides (HDPs) are short cationic peptides that play a key role in the innate immune response of all living organisms. Their action mechanism does not depend on the presence of protein receptors, but on their ability to target and disrupt the membranes of a wide range of pathogenic and pathologic cells which are recognized by their specific compositions, typically with a relatively high concentration of anionic lipids. Lipid profile singularities have been found in cancer, inflammation, bacteria, viral infections, and even in senescent cells, enabling the possibility to use them as therapeutic targets and/or diagnostic biomarkers. Molecular dynamics (MD) simulations are extraordinarily well suited to explore how HDPs interact with membrane models, providing a large amount of qualitative and quantitative information that, nowadays, cannot be assessed by wet-lab methods at the same level of temporal and spatial resolution. Here, we present SuPepMem, an open-access repository containing MD simulations of different natural and artificial peptides with potential membrane lysis activity, interacting with membrane models of healthy mammal, bacteria, viruses, cancer or senescent cells. In addition to a description of the HDPs and the target systems, SuPepMem provides both the input files necessary to run the simulations and also the results of some selected analyses, including structural and MD-based quantitative descriptors. These descriptors are expected to be useful to train machine learning algorithms that could contribute to design new therapeutic peptides. Tools for comparative analysis between different HDPs and model membranes, as well as to restrict the queries to structural and time-averaged properties are also available. SuPepMem is a living project, that will continuously grow with more simulations including peptides of different sequences, MD simulations with different number of peptide units, more membrane models and also several resolution levels. The database is open to MD simulations from other users (after quality check by the SuPepMem team). SuPepMem is freely available under https://supepmem.com/.