Antimicrobial peptides of multicellular organisms

AhR Activation Transcriptionally Induces Anti-Microbial Peptide Alpha-Defensin 1 Leading to Reversal of Gut Microbiota Dysbiosis and Colitis

Alpha-defensin 1 is a small antimicrobial peptide that acts as the first line of defense against pathogens. It is induced following microbial cues and inflammatory signals in neutrophils and Paneth cells in the small intestine, which suggests that it plays a role in microbial homeostasis in the gut. The gut microbial products also serve as ligands for the aryl hydrocarbon receptor (AhR), an environmental sensor. In the current study, we investigated if there is any crosstalk between AhR and alpha-defensin 1. Interestingly, we found a positive correlation between AhR and alpha-defensin 1 protein levels in ileal tissues from active Crohn's' (CD) patients and epithelial cells (IECs) from multiple models of murine colitis. In vitro downregulation of AhR led to inhibition of α-defensin 1, while activation of AhR induced α-defensin 1 in IECs. AhR directly targeted the dioxin response element 3 (DRE3) region on the α-defensin 1 promoter in IECs. AhR-mediated induction of α-defensin 1 in colitis mice reversed the gut microbial dysbiosis and alleviated colitis. Our data identify a novel signaling pathway in which AhR acts as a transcription factor for α-defensin 1, leading to regulation of homeostasis between gut microbiota, intestinal mucosa, and mucosal immunity.

Co-assembly of antimicrobial polypeptoids/carbon dots for internal-external cooperated sterilization

Bacterial infections have emerged as a significant global public health challenge that requires urgent attention. In the research of popular antimicrobial agents, antimicrobial peptide mimics with good properties have the disadvantage of high toxicity, and nanomaterials with metal-doped carbon dots as the most representative have the problems of easy agglomeration and insufficient bactericidal effect. Herein, combined therapeutic strategy was proposed to reach the best compromise and sterilization effects. We employed an electrostatic co-assembly strategy to combine nanomaterials iron-doped carbon dots (Fe-CDs) and antimicrobial polypeptoids Poly(N-allylglycine) modified with thiol-terminated amines (PNAG66-NH2), resulting in the creation of the antimicrobial composite Fe-CDs-PNAG66-NH2. Through electrostatic adsorption, the composite disrupts the electrostatic environment of the bacterial outer membrane, alters its permeability, and triggers an increase in intracellular reactive oxygen species (ROS) to rapidly kill 99.999% of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) within 10 min. It exhibited negligible cytotoxicity to normal cells. Furthermore, in vivo experiments demonstrated that Fe-CDs-PNAG66-NH2 accelerated the healing of infected wounds, reduced inflammation. The present study demonstrates that the efficient bactericidal properties of the complexes are triggered by the synergistic action of nanomaterials and antimicrobial polypeptoids, which provides a new strategy to achieve safe and efficient broad-spectrum bactericidal activity in antimicrobial aspects.

The mytilin gene cluster: Shedding light on the enigmatic origin of mussel dispensable genes

Mussels exhibit a sophisticated innate immune response characterized by many highly variable molecules responsible for recognizing and killing potential pathogenic microorganisms. The complexity of this molecular arsenal is marked by the occurrence of gene presence-absence (PAV), a phenomenon that targets numerous expanded lineage-specific gene families. This phenomenon enhances inter-individual sequence variability, further enriching the diversity of the repertoire of molecules involved in the immune response. Until now, the origin of mussel dispensable genes, which, unlike core genes, are not shared by all individuals, has remained elusive. In this study, by analyzing the resequenced genomes of more than 160 individuals in four distinct species of the Mytilus complex, we characterize the repertoire of mytilin genes encoding hemocyte-specific antimicrobial peptides (AMPs). We define a canonical gene architecture comprising four protein-coding genes and two pseudogenes in most haplotypes. However, the organization of the locus displays a marked intra-specific diversity due to the presence of variable alleles, the frequent pseudogenization of mytilin G1 and structural variants associated with additional dispensable mytilin genes, which often retain features that support functional preservation. Molecular phylogeny supports an ancient origin for dispensable mytilin genes, predating the radiation of modern Mytilus species. This suggests that most widespread extant haplotypes derive from a larger and more complex ancestral mytilin gene cluster and that dispensable mytilin genes are vestigial AMPs that have been retained only in a few populations where their presence may have contributed to fitness advantages and local adaptation.

Naturally inspired chimeric quinolone derivatives to reverse bacterial drug resistance

Antimicrobial resistance poses an urgent threat to global health, underscoring the critical need for new antibacterial drugs. Ciprofloxacin, a third-generation quinolone antibiotic, is used to treat different types of bacterial infections; however, it often results in the rapid emergence of resistance in clinical settings. Inspired by low susceptibility to antimicrobial resistance of natural antimicrobial peptides, we herein propose a host defense peptide-mimicking strategy for designing chimeric quinolone derivatives which may reduce the likelihood of antibacterial resistance. This strategy involves the incorporation of deliberately designed amphiphilic moieties into ciprofloxacin to mimic the structural characteristics and resistance-evading properties of host defense peptides. A resulting chimeric compound IPMCL-28b, carrying a rigid linker and three cationic amino acids along with a lipophilic acyl n-decanoyl tail, exhibited potent activity against a panel of multidrug-resistant bacterial strains by endowing the ciprofloxacin derivatives with additional ability to disrupt bacterial cell membranes. Molecular dynamics simulations showed that IPMCL-28b demonstrates significantly stronger disruptive interactions with cell membranes than ciprofloxacin. This compound not only demonstrated high selectivity with low hemolysis side effect, but also significantly reduced the likelihood of resistance development compared with ciprofloxacin. Excitingly, IPMCL-28b demonstrated highly enhanced in vivo antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) with a 99.99 % (4.4 log) reduction in skin bacterial load after a single dose. These findings highlight the potential of host defense peptides-mimicking amphiphilic ciprofloxacin derivatives to reverse antibiotic resistance and mitigate the development of antimicrobial resistance.

StxB fusion strategy for immunogenic enhancement: Recombinant expression of AcAMP antimicrobial peptide

BACKGROUND AND OBJECTIVES

Polyclonal antibodies are essential for identifying compounds like peptides. However, many peptides exhibit low immunogenicity, resulting in reduced antibody yields. To address this, fusing peptides with immunogenic fusion proteins has been proposed. This study aimed to enhance the immunogenicity of the AcAMP peptide by fusing it with StxB as a fusion protein, producing the recombinant construct in Escherichia coli, and comparing its antibody titration to recombinant AcAMP in mice.

METHODS

The acamp gene, containing BamHI and SalI restriction sites, was amplified from the pUC57 plasmid via PCR and cloned into the pET28a (+)-StxB expression vector. The pET28a (+)-AcAMP construct was prepared as previously described. Both constructs were expressed in E. coli BL21 (DE3) cells, induced with IPTG, and purified using nickel affinity chromatography. Recombinant proteins were confirmed by SDS-PAGE and Western blotting. Mice were immunized with purified proteins, and serum IgG titration was assessed using indirect ELISA.

RESULTS

PCR amplification and enzymatic digestion verified the successful construction of the pET28a (+)-StxB-acamp vector. SDS-PAGE and Western blotting identified recombinant AcAMP and AcAMP-StxB proteins at 9 and 17 kDa, respectively. ELISA revealed significantly higher antibody titers for the recombinant AcAMP-StxB protein compared to recombinant AcAMP.

CONCLUSION

Fusing the AcAMP peptide with the StxB protein enhanced immunogenicity and increased antibody production. This approach may improve expression conditions and immunogenicity for peptides of this family, advancing their use in identification studies.

Molecular transport through nano-sized multipores of lipid vesicles: a COMSOL simulation study

Biomembranes regulate molecular transport essential to cellular function and numerous biomedical applications, such as drug delivery and gene therapy. This study simulates molecular transport through nano-sized multipores in Giant Unilamellar Vesicles (GUVs) using COMSOL Multiphysics. We analyzed the diffusion dynamics of fluorescent probes-including Calcein, Texas-red dextran 3000 (TRD- 3k), TRD- 10k, and Alexa Fluor-labeled soybean trypsin inhibitor (AF-SBTI)-across different pore sizes, and derived rate constants using curve fitting that closely align with experimental data. Additionally, an analytical model based on Fick's law of diffusion provides further insight into transport efficiency. This approach offers a novel perspective by examining simultaneous transport through multiple nanopores, which better mimics realistic biological environments compared to traditional single-pore studies. We used COMSOL for efficiently simulating large-scale, multi-nanopore systems, particularly in biomedical applications where modeling of complex transport phenomena is essential. This work provides new insights into multipore-mediated transport, critical for optimizing nanopore-based drug delivery and advancing the understanding of cellular transport mechanisms.

Single-cell analysis of antimicrobial compound-induced cell death of bacterial cells

Due to the stochasticity of metabolic reactions and cell cycles of bacterial cells, it is necessary to examine the antibacterial activities of antimicrobial compounds (AMCs) such as antibiotics and antimicrobial peptides (AMPs) at the single-cell level. Here, we review recent studies of the bactericidal activities of AMCs at the single-cell level. First, we discuss recent investigations of the interaction of various AMPs with single bacterial cells, as monitored in real time using optical microscopy. This strategy provides information on AMP-induced membrane damage in single cells [e.g. the onset time of damage to the cell membrane (CM) and outer membrane of single cells]. The rate of AMP-induced CM damage is estimated as the fraction of cells with CM damage [Pdamage (t)] at a specific interaction time t. Second, we discuss the use of single-cell analysis of the bactericidal activity of AMCs. The fraction of dead cells after the exposure to AMCs for time t is determined as the fraction of the microcolonies containing only one cell [Psingle (t)]. For some AMPs, the Pdamage (t) and Psingle (t) values are similar, indicating that AMP-induced CM damage is the direct cause of cell death. Third, we discuss single-cell analysis of the processes and mechanisms of antibiotic-induced cell death. For example, fluoroquinolones and aminoglycosides are observed to induce cytoplasmic condensation and cell lysis, leading to cell death. Based on these studies, we provide our perspective on future investigations using single-cell analysis to assess the processes and the mechanisms of the bactericidal activities of AMCs.

From Antibacterial Activity to Molecular Mechanism: Case Study of Hexapeptide RWWRWW and Its Analogues

In recent years, antimicrobial peptides (AMPs) have emerged as a potent weapon against the growing threat of antibiotic resistance. Among AMPs, the ones containing tryptophan (W) and arginine (R) exhibit enhanced antimicrobial properties, benefiting from the unique physicochemical features of the two amino acids. Herein, we designed three hexapeptides, including WR, DWR (D-isomer), and RF, derived from the original sequence, RWWRWW-NH2 (RW). By combining sum frequency generation vibrational spectroscopy (SFG-VS) and molecular dynamics (MD) simulation, we examined AMPs' interactions with model bacterial membrane at the molecular level. Our findings revealed the innate different structural features associated with molecular aggregation and membrane activity between L-(WR, RF and RW) and D-isomer. The D-isomer was demonstrated to aggregate via intermolecular hydrogen bonding, which reduced its membrane adsorption quantity and consequently weakened its disruptive effect on the model membrane; while L-isomers rarely aggregated and thus could fully interact with the model membrane. D-isomer was proven to lack a stable helical structure, while L-isomers adopted helical structures, which was believed to be the reason for DWR's tendency to aggregate easily. This study should contribute to designing novel short-chain AMPs with high efficiency, especially in the case that D-isomers will be used.

An effective approach to obtain functional poly-β-peptides for combating drug-resistant bacterial infections

The high mortality of drug-resistant bacterial infections, especially those caused by multidrug-resistant Gram-negative pathogens, highlights an urgent demand for promising antimicrobial strategies. Host defense peptide (HDP)-mimicking poly-β-peptides have demonstrated significant potential in combating drug-resistant bacterial infections, with their antimicrobial activity closely dependent on their side-chain structures. However, the restricted structural diversity of poly-β-peptides necessitates efficient synthetic methods to expand their diversity, particularly positively charged side-chain structures. This study presents a water-tolerant approach that facilitates the controllable synthesis of poly-β-peptides with different chain lengths and structurally diverse side chains, including primary amines, tertiary amines, as well as alkyl, aryl, and methoxy groups. This approach serves as an HDP-mimicking discovery platform to obtain the optimal poly-β-peptide, AOc0.8HNL0.2, which exhibits broad-spectrum antibacterial activity and high selectivity against drug-resistant bacteria. The antibacterial mechanism studies reveal that AOc0.8HNL0.2 disrupts the membrane of Gram-negative bacteria. In vivo evaluations substantiate the therapeutic potential of AOc0.8HNL0.2 in treating drug-resistant bacterial infections with no observable toxicity. This study underscores the potential of this convenient synthetic strategy as a promising platform for developing antimicrobial poly-β-peptides to combat the growing threat of drug-resistant bacterial infections.

Engineered Macrophage Membrane-Camouflaged Nanodecoys Reshape the Infectious Microenvironment for Efficient Periodontitis Treatment

A vicious cycle between microbiota dysbiosis and hyperactivated inflammation, hardly disrupted by conventional therapies, remains a significant clinical challenge for periodontitis treatment. Herein, by cloaking a cascade catalysis system in an engineered macrophage membrane, a nanodecoy-based strategy, with targeted bacteria-killing and immunomodulatory abilities, is proposed for reshaping the hostile periodontitis microenvironment. Specifically, recombinant human antimicrobial peptide, LL-37, is anchored to a Toll-like receptor-enriched macrophage membrane via genetic engineering, which facilitates the specific bacteria elimination and efficient tissue retention of the nanodecoys. Moreover, the cascade catalysis system integrates L-amino acid oxidase (LAAO) with hollowed manganese dioxide (hMnO2) by reciprocal elevation of the catalytic efficiency of hMnO2 and LAAO, leading to accelerated O2 generation under a hypoxic microenvironment and disrupted metabolism of periodontopathogenic bacteria. Notably, the nanodecoys trigger the nuclear translocation of NF-E2-related factor-2 (NRF2) to reduce oxidative stress response and rewire the polarization of macrophages, thereby boosting the osteogenic differentiation of osteoblasts. Furthermore, the alveolar bone regeneration therapeutically benefits from the nanodecoys in vivo. Altogether, these results highlight the attractive functions of engineered macrophage membrane-cloaked nanodecoys for effective periodontitis treatment.

Filamentous bacteriophage M13 induces proinflammatory responses in intestinal epithelial cells

Bacteriophages are the dominant members of the human enteric virome and can shape bacterial communities in the gut; however, our understanding of how they directly impact health and disease is limited. Previous studies have shown that specific bacteriophage populations are expanded in patients with Crohn's disease (CD) and ulcerative colitis (UC), suggesting that fluctuations in the enteric virome may contribute to intestinal inflammation. Based on these studies, we hypothesized that a high bacteriophage burden directly induces intestinal epithelial responses. We found that filamentous bacteriophages M13 and Fd induced dose-dependent IL-8 expression in the human intestinal epithelial cell line HT-29 to a greater degree than their lytic counterparts, T4 and ϕX174. We also found that M13, but not Fd, reduced bacterial internalization in HT-29 cells. This led us to investigate the mechanism underlying M13-mediated inhibition of bacterial internalization by examining the antiviral and antimicrobial responses in these cells. M13 upregulated type I and III IFN expressions and augmented short-chain fatty acid (SCFA)-mediated LL-37 expression in HT-29 cells. Taken together, our data establish that filamentous bacteriophages directly affect human intestinal epithelial cells. These results provide new insights into the complex interactions between bacteriophages and the intestinal mucosa, which may underlie disease pathogenesis.

Rapid Response Antimicrobial Peptide Design Strategy Driven by Meta-Learning for Emerging Drug-Resistant Pathogens

Antimicrobial resistance (AMR) presents a critical global health threat requiring urgent intervention. In order to swiftly respond to and control the spread of emerging drug-resistant bacteria at the onset of their proliferation, our aim is to develop a Rapid Response Antimicrobial Peptide (AMP) design strategy (RR-ADS). This framework addresses the challenge of limited pathogen-specific data by achieving robust generalization from minimal samples by meta-learning and reinforcement learning, optimizing both biocompatibility and efficacy against drug-resistant pathogens. Our model has achieved satisfactory results across multiple evaluation metrics, demonstrating the capability to accurately identify and generate AMPs targeted against drug-resistant bacteria with minimal sample sizes. Within 2 weeks, we successfully designed and experimentally verified AMPs against multidrug-resistant Acinetobacter baumannii, achieving a 93.3% positive rate. RR-ADS has effectively demonstrated the potential of meta-learning in tasks involving bioactive peptides and holds promise as an effective alternative measure to address infectious disease public health emergencies.

Evaluating the Antimicrobial Efficacy of TroLEAP2 like-27 peptide in golden pompano (Trachinotus ovatus) against Bacterial Pathogens

Amicrobial peptides are crucial components of immune system, acting as the first line of defense against microbial invasion. This study investigated the antimicrobial activity of TroLEAP2 like-27, a novel 27-amino acid peptide derived from golden pompano (Trachinotus ovatus), against Gram-positive Lactococcus garvieae and Staphylococcus epidermidis, and Gram-negative Vibrio alginolyticus and Vibrio harveyi. The 3D structure and helical wheel presentation of TroLEAP2 like-27 were consistent with typical AMP features. The hydrophobic ratio of TroLEAP2 like-27 was 47 %, and its α-helical structure suggested strong antimicrobial potential. The expression levels of the TroLEAP2 like gene in the liver and intestines tissues of T. ovatus were significantly upregulated following infection with L. garvieae and V. harveyi. The peptide induced bacterial agglutination in the presence of Ca2+ and exhibited bactericidal activity with a MIC50 of 60 μM. Transmission electron microscopy (TEM) revealed structural damage to bacterial membranes, while membrane permeability assays showed dose-dependent disruption and depolarization in all tested strains. Additionally, TroLEAP2 like-27 exhibited a potent capacity to interact with and degrade genomic DNA of all tested bacteria. The peptide treatment significantly reduced bacterial loads in the gill, liver, and intestinal tissues of the fish, with histological analysis revealing a remarkable protective effect on the tissues. Furthermore, fish treated with TroLEAP2 like-27 exhibited improved survival rates following bacterial infection. These findings suggest that TroLEAP2 like-27 is a promising antimicrobial peptide with potential therapeutic applications.

Isolation and characterization of antimicrobial peptides from Lactobacillus: Exploring mechanisms of action

The rise of antibiotic-resistant bacteria necessitates the development of novel antimicrobial agents. In this study, antimicrobial peptides (AMPs) were isolated from Lactobacillus sp., yielding Bioactive Peptide I (BAP I) and Bioactive Peptide III (BAP III). Purified via gel filtration chromatography (GFC), these peptides were characterized by MALDI-TOF MS and SDS-PAGE, which confirmed their molecular masses as 4168.14 Da and 8076.45 Da, respectively, and verified their high purity. Both peptides demonstrated potent antibacterial activity against Pseudomonas aeruginosa, Streptococcus sanguinis, Bacillus cereus, and Staphylococcus aureus, with BAP I exhibiting superior efficacy. This enhanced activity is likely due to its amphipathic structure and hydrophobic C-terminal region, which promote effective bacterial membrane disruption as evidenced by FE-SEM imaging. In addition to compromising membrane integrity, both BAP I and BAP III inhibited bacterial DNA polymerase activity, as shown by reduced PCR product formation. Complementary Circular Dichroism (CD) spectroscopy analysis indicated that peptide binding induced conformational changes in Taq polymerase, reducing its α-helical and β-sheet content while increasing the proportion of random coil structures-thus enhancing the enzyme's flexibility. Molecular docking and dynamics studies further revealed stable interactions between the peptides and the enzyme, suggesting a dual mechanism of action that targets both the bacterial membrane and DNA replication processes. Collectively, these findings highlight the significant potential of BAP I and BAP III as novel antimicrobial agents against multidrug-resistant infections. Future research should focus on evaluating their safety and clinical efficacy, as well as exploring their synergistic potential with existing antibiotics to advance these peptides as therapeutic alternatives.

The topical application of Sphistin12-38 in combination with sponge spicules for the acne treatment

We demonstrated for the first time that a marine-derived antimicrobial peptide (AMP), Sph12-38, exhibit high antimicrobial activity against P. acnes with a minimum bactericidal concentration (MBC) value of 7 μM. Meanwhile, Sph12-38 has no significant cytotoxicity to human keratinocytes (HKs) at its high concentration (33.5 μM). The topical application of sponge Haliclona sp. spicules (SHS) dramatically enhanced the skin penetration of Sph12-38 up to 40.9 ± 5.9% (p < 0.01), which was 6.1 ± 0.9-fold higher than that of Sph12-38 alone. Further, SHS resulted in the accumulation of most Sph12-38 in viable epidermis and dermis. Further, the combined use of Sph12-38 and SHS resulted in a cure rate of 100% for rabbit ear acne treatment in vivo for two weeks, while the one induced by other groups was 40%, 0% and 0% for SHS alone, Sph12-38 alone and control group, respectively. The strategy of combined using AMP and SHS can also be applied in a rational designed topical delivery system for the management of other deep infection of the skin. The effectiveness of SHS by itself on the treatment of acne was also demonstrated by clinical trials. After 14 days of treatment by 1% SHS gel. The number of skin lesions decreased by 51.4%.

Charge, Hydrophobicity, and Lipid Type Drive Antimicrobial Peptides' Unique Perturbation Ensembles

Antimicrobial peptides (AMPs) have emerged as a promising solution to the escalating public health threat caused by multidrug-resistant bacteria. Although ongoing research efforts have established AMP's role in membrane permeabilization and leakage, the precise mechanisms driving these disruption patterns remain unclear. We leverage molecular dynamics (MD) simulations enhanced by membrane mimetic (HMMM) to systematically investigate how the physiochemical properties of magainin (+3) and pexiganan (+9) affect their localization, insertion, curvature perturbation, and membrane binding ensemble. Building on existing microbiology, NMR, circular dichroism, and fluorescence data, our analysis reveals that the lipid makeup is a key determinant in the binding dynamics and structural conformation of AMPs. We find that phospholipid type is crucial for peptide localization, demonstrated through magainin's predominant interaction with lipid tails and pexiganan's with polar headgroups in POPC/POPS membranes. The membrane curvature changes induced by pexiganan relative to magainin suggest that AMPs with larger charges have more potential in modulating bilayer bending. These insights advance our understanding of AMP-membrane interactions at the molecular level, offering guidance for the design of targeted antimicrobial therapies.

D-M159 Synergistically Induces Apoptosis in HeLa Cells Through Endoplasmic Reticulum Stress and Mitochondrial Dysfunction

Pore-forming peptides are promising antimicrobial and anticancer agents due to their membrane selectivity and biodegradability. Our prior work identified peptide M159, which permeabilized synthetic phosphatidylcholine liposomes without mammalian cell toxicity. Here, we report that the D-type variant (D-M159) induces apoptosis in HeLa cells under starvation. To explore its anticancer mechanism, we analyzed D-M159 cytotoxicity, intracellular uptake, and apoptotic pathways via flow cytometry, confocal microscopy, and Western blot. Calcium dynamics and mitochondrial function were examined via specific labeling and functional assays. Results revealed that D-M159 exhibited starvation-dependent, dose-responsive cytotoxicity and triggered apoptosis in HeLa cells. Mechanistic studies indicated that D-M159 entered the cells via caveolin-dependent and caveolae-dependent endocytosis pathways and induced endoplasmic reticulum stress in HeLa cells by up-regulating proteins such as ATF6, p-IRE1, PERK, GRP78, and CHOP. Meanwhile, D-M159 promoted the expression of IP3R1, GRP75, and VDAC1, which led to mitochondrial calcium iron overload, decreased mitochondrial membrane potential, and increased reactive oxygen species (ROS) generation, thereby activating the mitochondrial apoptotic pathway and inducing the aberrant expression of Bax, Bcl-2, Caspase-9, and Caspase-3. This study showed that D-M159 synergistically induced apoptosis in starved HeLa cells through endoplasmic reticulum stress and mitochondrial dysfunction, demonstrating its potential as a novel anticancer agent.

Machine learning-driven discovery of highly selective antifungal peptides containing non-canonical β-amino acids

Antimicrobial peptides (AMPs) are promising compounds for the treatment and prevention of multidrug-resistant infections because of their ability to directly disrupt microbial membranes, a mechanism that is less likely to lead to resistance compared to antibiotics. Unfortunately, natural AMPs are prone to proteolytic cleavage in vivo and have relatively low selectivity for microbial versus human cells, motivating the development of synthetic peptidomimetics of AMPs with improved peptide stability, activity, and selectivity. However, a lack of understanding of structure-activity relationships for peptidomimetics constrains development to rational design or experimental predictors, both of which are cost and time prohibitive, especially when the design space of possible sequences scales exponentially with the number of amino acids. To address these challenges, we developed an iterative Gaussian process regression (GPR) approach to explore a large design space of 336 000 synthetic α/β-peptide analogues of a natural AMP, aurein 1.2, based on an initial training set of 147 sequences and their biological activities against microbial pathogens and selectivity for microbes vs. mammalian cells. We show that the quantification of prediction uncertainty provided by GPR can guide the exploration of this design space via iterative experimental measurements to efficiently discover novel sequences with up to a 52-fold increase in antifungal selectivity compared to aurein 1.2. The highest selectivity peptide discovered using this approach features an unconventional substitution of cationic amino acids in the hydrophobic face and would be unlikely to be explored by conventional rational design. Overall, this work demonstrates a generalizable approach that integrates computation and experiment to accurately predict the selectivity of AMPs containing synthetic amino acids, which we employed to discover new α/β-peptides that hold promise as selective antifungal agents to combat the antimicrobial resistance crisis.

A plant peptide with dual activity against multidrug-resistant bacterial and fungal pathogens

Multidrug-resistant (MDR) bacteria pose a major threat to public health, and additional sources of antibacterial candidates are urgently needed. Noncanonical peptides (NCPs), derived from noncanonical small open reading frames, represent small biological molecules with important roles in biology. However, the antibacterial activity of NCPs remains largely unknown. Here, we discovered a plant-derived noncanonical antibacterial peptide (NCBP1) against both Gram-positive and Gram-negative bacteria. NCBP1 is composed of 11 amino acid residues with cationic surface potential and favorable safety and stability. Mechanistic studies revealed that NCBP1 displayed antibacterial activity by targeting phosphatidylglycerol and cardiolipin in bacterial membrane, resulting in membrane damage and dysfunction. Notably, NCBP1 showed promising efficacy in mice. Furthermore, NCBP1 effectively inhibited the growth of plant fungal pathogens and enhanced disease resistance in maize. Our results demonstrate the unexplored antimicrobial potential of plant-derived NCPs and provide an accessible source for the discovery of antimicrobial substances against MDR bacterial and fungal pathogens.

Lipid Shape as a Membrane Activity Modulator of a Fusogenic Antimicrobial Peptide

An intriguing feature of many bacterial membranes is their prevalence of non-bilayer-forming lipids, such as the cone-shaped phosphatidylethanolamines and cardiolipins. Many membrane-active antimicrobial peptides lower the bilayer-to-hexagonal phase transition energy barrier in membranes containing such types of cone-shaped lipids. Here, we systematically studied how the molecular shape of lipids affects the activity of antimicrobial peptide EcDBS1R4, which is known to be an efficient fusogenic peptide. Using coarse-grained molecular dynamics simulations, we show the ability of EcDBS1R4 to form "hourglass-shaped" pores, which is inhibited by cone-shaped lipids. The abundance of cone-shaped lipids further correlates with the propensity of this peptide to oligomerize preferentially in antiparallel dimers. We also observe that EcDBS1R4 promotes the segregation of the anionic lipids. When coupled to dimerization, this charge segregation leads to regions in the bilayer that are devoid of peptides and rich in zwitterionic lipids. Our results indicate a protective role of cone-shaped lipids in bacterial membranes against pore-mediated permeabilization by EcDBS1R4.

Unlocking the Potential of Antimicrobial Peptides: Cutting-Edge Advances and Therapeutic Potential in Combating Bacterial Keratitis

Bacterial keratitis is a prevalent, and severe corneal illness resulting from bacterial pathogens. Failure to administer a timely and suitable therapy may lead to corneal opacity, ulceration, significant vision impairment, or potential blindness. Current clinical interventions for bacterial keratitis involve the administration of topical antimicrobial agents and systemic antibiotics. However, the misuse and overuse of antibiotics have led to the rapid emergence of antibiotic-resistant bacteria. Additionally, the restricted antibacterial spectrum and possible adverse effects of antibiotics have provided considerable obstacles to traditional therapies. This highlights the urgent need for novel and highly effective antimicrobial agents. Antimicrobial peptides (AMPs) are a class of naturally occurring or synthetically designed small molecules that have gained significant attention due to their unique antimicrobial mechanisms and low risk of resistance development. AMPs exhibit promising potential in treating bacterial keratitis through direct antibacterial mechanisms, such as inhibiting cell wall synthesis, disrupting cell membranes, and interfering with nucleic acid metabolism, as well as indirect mechanisms, including modulation of the host immune response. This review provides a comprehensive overview of the antibacterial mechanisms of AMPs and their advancements in the treatment of bacterial keratitis. It emphasizes the role of various modification strategies and artificial-intelligence-assisted design in enhancing the antibacterial efficacy, stability, and biocompatibility of AMPs. Furthermore, this review discusses the latest progress in combining AMPs with delivery systems for improved therapeutic outcomes. Finally, the review highlights the current challenges and future perspectives of AMPs in bacterial keratitis treatment, providing valuable insights for developing novel AMPs with high antibacterial efficacy, stability, and safety for bacterial keratitis therapies.

Advancements in Regenerative Therapies for Orthopedics: A Comprehensive Review of Platelet-Rich Plasma, Mesenchymal Stem Cells, Peptide Therapies, and Biomimetic Applications

Background/Objectives: Regenerative therapies have gained interest in orthopedic applications for their potential to enhance tissue regeneration, functional recovery, and pain modification. This review evaluates the clinical efficacy of platelet-rich plasma (PRP), mesenchymal stem cells (MSCs), peptide-based treatments, and biomimetic materials in orthopedic care, with a focus on pain reduction and functional outcomes. Methods: A structured literature search in PubMed (January 2009-January 2025) identified 160 studies. After applying inclusion criteria prioritizing randomized controlled trials (RCTs) and clinical trials, 59 studies were included: 20 on PRP, 20 on MSCs, 10 on peptide therapies, and 7 on biomimetics. Data extraction focused on pain reduction and functional recovery, with risk of bias assessed using the Cochrane Risk of Bias (RoB) tool and ROBINS-I tool. A random-effects meta-regression analysis was conducted to evaluate the impact of therapy type, sample size, and risk of bias on reported pain reduction outcomes. Results: Meta-regression analysis identified MSC therapy as the most effective intervention for pain reduction (β = 8.45, p < 0.05), with PRP and peptide-based therapies showing moderate improvements, and biomimetic therapies demonstrating the lowest effect. PRP provided short-term pain relief, particularly in acute injuries and tendon repair, though inconsistencies in preparation methods limited success in chronic conditions. MSC therapies demonstrated cartilage regeneration and early osteoarthritis improvement, but high costs and ethical concerns remain barriers to widespread adoption. Peptide-based therapies and biomimetic materials, including engineered scaffolds and autologous protein solutions, showed promise for infection control and wound healing, though further research is needed to optimize dosing, delivery methods, and long-term safety. Conclusions: Regenerative therapies offer significant potential in orthopedic care, with MSC therapies demonstrating the most reliable regenerative effects, PRP providing short-term symptomatic relief, and peptide-based and biomimetic treatments emerging as promising adjuncts. However, standardized protocols and large-scale clinical trials are needed to establish long-term efficacy and improve clinical translation for broader adoption.

Proline-Modified (RW)n Peptides: Enhancing the Antimicrobial Efficacy and Selectivity against Multidrug-Resistant Pathogens

The growing threat of multidrug-resistant (MDR) bacteria necessitates the development of novel antimicrobial agents. This study investigates the potential of proline-modified (RW)n peptides as a platform for combating MDR pathogens with minimal toxicity. We synthesized and evaluated (RW)n peptides (n = 4, 6, and 8) with and without central proline residues against five clinically relevant bacterial strains, including ESKAPE pathogens. Antimicrobial activity, cytotoxicity, and synergistic effects with conventional antibiotics were assessed. Proline incorporation significantly enhanced the peptide selectivity and broadened the spectrum of activity, particularly against Gram-negative bacteria. RW6P and RW8P demonstrated exceptional efficacy (MICs ≤ 0.25 μg/mL) against methicillin-resistant Staphylococcus aureus and Escherichia coli with minimal toxicity to human cells. Notably, RW8P restored ampicillin susceptibility in Pseudomonas aeruginosa (MIC < 0.25 μg/mL) without dose-dependent toxicity. Exceptionally, RW6-2P demonstrated efficacy against all Gram-positive and Gram-negative bacteria, except Klebsiella pneumoniae (Kp), without toxicity. Furthermore, several Gram-negative isolates were rendered susceptible to vancomycin when combined with these peptides, addressing a key limitation of glycopeptide antibiotics. Gram-negative Klebsiella pneumoniae (Kp) was rendered susceptible to vancomycin when combined with RW4P and RW6-2P. RW4P and RW6-2P, with and without antibiotics, have shown selectivity. This study presents proline-modified (RW)n peptides as promising candidates for developing broad-spectrum antimicrobials with enhanced selectivity and the potential to revitalize existing antibiotics against MDR pathogens.

Computational analysis of antimicrobial peptides targeting key receptors in infection-related cardiovascular diseases: molecular docking and dynamics insights

Infection-related cardiovascular diseases (CVDs) pose a significant health challenge, driving the need for novel therapeutic strategies to target key receptors involved in inflammation and infection. Antimicrobial peptides (AMPs) show the potential to disrupt pathogenic processes and offer a promising approach to CVD treatment. This study investigates the binding potential of selected AMPs with critical receptors implicated in CVDs, aiming to explore their therapeutic potential. A comprehensive computational approach was employed to assess AMP interactions with CVD-related receptors, including ACE2, CRP, MMP9, NLRP3, and TLR4. Molecular docking studies identified AMPs with high binding affinities to these targets, notably Tachystatin, Pleurocidin, and Subtilisin A, which showed strong interactions with ACE2, CRP, and MMP9. Following docking, 100 ns molecular dynamics (MD) simulations confirmed the stability of AMP-receptor complexes, and MM/PBSA calculations provided quantitative insights into binding energies, underscoring the potential of these AMPs to modulate receptor activity in infection and inflammation contexts. The study highlights the therapeutic potential of Tachystatin, Pleurocidin, and Subtilisin A in targeting infection-related pathways in CVDs. These AMPs demonstrate promising receptor binding properties and stability in computational models. Future research should focus on in vitro and in vivo studies to confirm their efficacy and safety, paving the way for potential clinical applications in managing infection-related cardiovascular conditions.

Knowledge mapping and research trends of cathelicidin peptide LL-37 from 1995 to 2024: a bibliometric study

BACKGROUND

To conduct a comprehensive bibliometric analysis of LL-37, summarize its development trends and patterns, and identify emerging research hotspots.

METHODS

Bibliometric and Knowledge Graph Analysis of Literature Data Related to LL-37 in the WOSCC Database Using Citespace and Vosviewer.

RESULTS

A total of 2,814 articles were analyzed, revealing a steady increase in recent publications. The USA and Sweden were the main contributors, with PLOS One publishing the most articles. Research on LL-37 in cancer and mast cells is emerging as a new focus.

CONCLUSION

The research status and development trends of LL-37 were quantitatively analyzed, providing new directions for future studies.

Amphipathic Antimicrobial Peptides Illuminate a Reciprocal Relationship Between Self-assembly and Cytolytic Activity

Amphipathic character, encoded within the polar sequence patterns of antimicrobial peptides, is a critical structural feature that influences membrane disruptive behavior. Similarly, polar sequence patterns induce self-assembly of amphipathic peptides, which results in the formation of ordered supramolecular structures. The relationship between self-assembly and membrane activity remains an open question of relevance for the development of effective antimicrobial peptides. Here, we report the structural investigation of a class of lytic peptides that self-assemble into filamentous nanomaterials. CryoEM analysis was employed to determine the structure of one of the filaments, which revealed that the peptides are self-assembled into a bilayer nanotube, in which the interaction between layers of amphipathic α-helices was mediated through hydrophobic interactions. The relative stability of the filament peptide assemblies depended on the influence of sequence modifications on the helical conformation. Antimicrobial assays indicated that cytolytic activity was associated with dynamic disassociation of the filamentous assemblies under the assay conditions. Structural modifications of the peptides that stabilized the filaments abrogated lytic activity. These results illuminate a reciprocal relationship between self-assembly and antimicrobial activity in this class of amphipathic peptides and that reversible assembly was critical for the observation of biological activity.

Cyclization of Two Antimicrobial Peptides Improves Their Activity

One promising strategy to combat worldwide antimicrobial resistance involves using cyclic peptides as antibacterial agents. Cyclization of peptides can confer several advantages, including enhanced stability to proteolysis, decreased toxicity and increased bactericidal efficacy. This paper examines two cyclic peptides CE-03 (12 AAs) and CE-05 (16 AAs) and evaluates their effectiveness in combating bacterial infections, their stability and toxicity. We compare them to their linear versions. Circular dichroism (CD) reveals that CE-03 and CE-05 both adopt random coil and β-sheet structures in lipid model membranes (LMMs) mimicking G(-) and G(+) bacteria, where they are both bactericidal. Using X-ray diffuse scattering (XDS), their effects on lipid model membranes show a deep penetration of both peptides into eukaryotic LMMs where they are nontoxic, while a headgroup location in bacterial LMMs correlates with bacterial killing. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Further, solution small-angle X-ray scattering demonstrates that both peptides induce vesicle fusion in bacterial LMMs without affecting eukaryotic LMMs. Proteolytic degradation studies show that both CE-05 and CE-03 do not lose activity when incubated with the elastase enzyme, while the helical E2-35 AMP becomes inactive upon proteolysis.

Stigmurin encapsulated PLA-PEG ameliorates its therapeutic potential, antimicrobial and antiproliferative activities

In light of growing global challenge posed by antimicrobial resistance, it is very important to explore alternatives that can target pathogenic microorganisms. One such strategy involves the use of antimicrobial peptides (AMPs) and Stigmurin is one such AMP present in Brazilian scorpion Tityus stigmurus which possesses antimicrobial, antiproliferative and antiparasitic activity. The study commenced with successful synthesis and characterization of Stigmurin and its analogues, designated S1 and S2. Studies on Stigmurin and its analogues have demonstrated that analogues exhibit enhanced antimicrobial efficacy but often lead to increased hemolysis, limiting their therapeutic application. To prevent the associated toxicity of these peptides, PLA-PEG di-block copolymer was synthesised to prepare nanoparticles (E-WT, E1, and E2) with an average diameter of approximately 160-180 nm. The core of the research involved evaluating the antimicrobial (Bacillus subtilis), antibiofilm (B. subtilis and Pseudomonas aeruginosa), antiproliferative (HEK293 and RAW264.7) and hemolytic activity of the peptides. In addition to the experimental work, in silico analysis using structural models was conducted to further understand their potential interactions. The findings demonstrated that the analogue peptides exhibit enhanced antimicrobial and antibiofilm activity compared to the wild-type Stigmurin. Moreover, encapsulating the peptides in PLA-PEG nanoparticles maintained the antimicrobial activity against B. subtilis. Further, encapsulation significantly reduced hemolysis as well as cytotoxicity by 10-20%, thereby improving their safety profile.

Membrane lipid composition directs the cellular selectivity of antimicrobial metallohelices

Two enantiomeric pairs of iron(ii) metallohelices, available as water-soluble, stable, and optically pure bimetallic complexes, differ principally in the length of the central hydrophobic region between two cationic domains, and have distinct activity and cell selectivity profiles against Gram-positive and Gram-negative microbes. The effects of dose concentration and temperature on levels of intracellular accumulation in E. coli and S. aureus, studied via isotopic labelling, indicate that the metallohelices enter the microbial cells via passive diffusion, whereupon (as previously determined) they act on intracellular targets. Whilst the metallohelices with the shorter central hydrophobic regions accumulate less readily than those with the longer hydrophobic bridge in both E. coli and S. aureus cells when incubated at the same concentration, an order of magnitude less is actually required per cell to inhibit growth in E. coli, hence they are more active. Furthermore, these more Gram-negative active compounds (with the shorter central hydrophobic region) are less toxic towards human APRE-19 mammalian cells and equine red blood cells. We hypothesise that these cell selectivities originate from the membrane composition. Dynamic light scattering and zeta potential measurements demonstrate that the more lipophilic metallohelices interact more strongly with the membrane-mimetic vesicles, notably in the charge-neutral mammalian model; thus the selectivity is not simply a result of electrostatic effects. For the less lipophilic metallohelices we observe that the binding affinity with the E. coli model vesicles is greater than with S. aureus vesicles, despite the lower negative surface charge, and this corresponds with the cellular accumulation data and the measured MICs. Specifically, the presence of membrane phosphatidylethanolamine (POPE) significantly increases the binding affinity of these metallohelices, and we postulate that a high proportion of such conical, non-lamellar phospholipids is important for metallohelix transport across the membrane. The metallohelices with the shorter hydrophobic bridge studied have a balance of charge and lipophilicity which allows selective cell entry in E. coli over mammalian cells, while the more lipophilic metallohelices are membrane promiscuous and unselective.

Characterization of avian β-defensin genes in Galliformes reveals widespread evolutionary diversification and distinct evolutionary relationships with infection risk

BACKGROUND

Avian β-defensins (AvBDs) represent a key family of antimicrobial host defense peptides in birds. Accumulating evidence suggests that the evolutionary trajectory of β-defensin genes is specific to the gene, timescale, and species involved, implying that species-specific ecological and life-history differences drive divergent selective pressures on these genes. However, their evolutionary dynamics, particularly the interactions with ecological factors and life-history traits, remain insufficiently explored.

RESULTS

Through a comprehensive survey of 25 species spanning all major clades of Galliformes, 354 AvBD genes were identified. Comparative sequence analysis, genomic organization, and phylogenetic studies collectively reveal significant evolutionary diversification characterized by gene duplication, pseudogenization, and gene loss across these species. Notably, chicken AvBD3 exhibits significant differences in its coding regions, while AvBD6 and AvBD7 appear to have copy number variations, with species-specific paralogs of AvBD6 being especially prominent. Moreover, positive selection was more frequently observed in recently diverged gene lineages compared to ancestral ones. Using 70 samples from eight galliform species, the study further identified the prevalence of species-specific amino acid alleles. Phylogenetic comparative analysis demonstrated that the evolution of nine AvBD genes (AvBD2, -4, -5, -8, -9, -10, -11, -12, and -14) is significantly associated with specific ecological factors and life-history characteristics. Additionally, the evolutionary rates of these genes showed distinct relationship with inferred infection risk, likely reflecting the multifunctionality of β-defensins and potential trade-offs between immune defense and other biological functions.

CONCLUSIONS

This cross-species identification and systematic evolutionary analysis of AvBDs in Galliformes deepen our understanding of the co-evolution of host defense peptides, offering valuable insights into their natural biology and evolution, and paving the way for future applications as alternatives to traditional antibiotics.

Antibacterial coatings for dental implants: A systematic review

OBJECTIVES

Despite the high survival rates of dental implants, peri-implantitis is a prevalent complication. Peri-implantitis is related to biofilm that adheres to the surface of implants and causes peri-implant chronic inflammation and bone destruction. Different surface treatments have been proposed to prevent biofilm formation. The objective of this systematic review was analyzing different types of antimicrobial coatings and identifying the most effective one(s) to control bacterial colonization over extended periods of analysis.

DATA, SOURCES AND STUDY SELECTION

We performed a bibliographic search in Pubmed and Cochrane base of articles published after 2010 to answer, according to the PICO system, the following question: What is the most effective antibacterial surface coating for dental implants? Only papers including a minimum follow-up bacteria growth analysis for at least 48 h were selected. After selection, the studies were classified using the PRISMA system. A total of 40 studies were included.

CONCLUSIONS

Three main categories of coatings were identified: Antibacterial peptides, synthetic antimicrobial molecules (polymers, antibiotics, …), and metallic nanoparticles (silver). Antibacterial peptide coatings to modify dental implant surfaces have been the most studied and effective surface modification to control bacterial colonization over extended periods of incubation as they are highly potent, durable and biocompatible. However, more in vitro and pre-clinical studies are needed to assess their true potential as a technology for preventing peri-implant infections.

Nano-viscosimetry analysis of membrane disrupting peptide magainin2 interactions with model membranes

The rapid spread of antibiotic-resistant strains of bacteria has created an urgent need for new alternative antibiotic agents. Membrane disrupting antimicrobial peptides (AMPs): short amino acid sequences with bactericidal and fungicidal activity that kill pathogens by permeabilizing their plasma membrane may offer a solution for this global health crisis. Magainin 2 is an AMP secreted by the African clawed frog (Xenopus laevis) that is described as a toroidal pore former membrane disrupting AMP. Magainin 2 is one of the most thoroughly studied AMPs, yet its mechanism of action is still largely hypothetical: visual evidence of the pore formation is lacking, and the molecular mechanism leading to pore formation is still debated. In the present study, quartz crystal microbalance (QCM) based viscoelastic fingerprinting analysis supported by dye leakage experiments and atomic force microscopy (AFM) imaging was used to glean deeper insights into the mechanism of action. The effect of membrane charge, acyl chain unsaturation and cholesterol concentration were also investigated. The results show lipid specific disruptive mechanism of magainin 2. QCM nano-viscometry measurements revealed the presence of distinct stages in the mechanism of magainin 2 action that, with dye leakage data, confirm the existence of an initial transient pore stage that may result in peptide flip-flop between the outer and inner membrane leaflets. There is evidence of a further mechanistic stage at high peptide concentrations that is consistent with membrane collapse into a peptide-lipid mixed phase that is distinct from the transient pore formation. The results confirm some of the earliest hypotheses about magainin 2 action, while also highlighting the membrane modulating effect of this peptide.

Uncovering the potent antimicrobial activity of squaramide based anionophores - chloride transport and membrane disruption

Antimicrobial resistance (AMR) - often referred to as a silent pandemic, is at present the most serious threat to medicine, and with constantly emerging resistance to novel drugs, combined with the paucity of their development, is likely to worsen. To circumvent this, supramolecular chemists have proposed the applicability of synthetic anion transporters in the fight against AMR. In this article we discuss the synthesis, supramolecular characterisation and biological profiling of six structurally simple squaramide anion transporters. Through a combination of spectroscopic techniques, and cellular assays we have deduced the mode of action of these antimicrobial agents to be as a result of both anion transport and membrane disruption. Furthermore, through the synthesis of two fluorescent analogues we verified this membrane-localised activity using Super-Resolution nanoscopy methods. These compounds represent particularly active antimicrobial anionophores and compliment similar reports showing the applicability of agents such as these in the fight against AMR.

Antimicrobial Peptides: Classification, Mechanism, and Application in Plant Disease Resistance

Antimicrobial peptides (AMPs) are a class of alkaline, small molecules found widely in nature. This article surveys the classifications of AMPs, delving into their modes of action and their role in controlling significant plant diseases caused by bacteria, viruses, and fungi. It also explores the prospects and challenges in this field, aiming to provide insights for enhancing crop disease resistance, ensuring food security, deepening the understanding of pathogen mechanisms, and protecting ecological balance.

Single Amino Acid Changes Impact the Ability of Drosophila melanogaster Cecropins to Inhibit Growth of Providencia Pathogens

As antibiotic-resistant bacteria spread worldwide, the need to develop novel antimicrobial agents is urgent. One rich source of potential antimicrobials is the insect immune system, as insects produce a wide range of antimicrobial peptides (AMPs) with diverse sequences and structures. Insects also encounter many bacterial pathogens, some of which are closely related to pathogens of clinical relevance. However, despite interest in AMPs as therapeutics, the relationships between the amino acid sequence, biophysical properties, antimicrobial activity, and specificity are still not generalizable. To improve our understanding of these relationships, we assessed how single amino acid changes in cecropin AMPs produced by the fruit fly, Drosophila melanogaster, impact both their structure and their ability to inhibit the growth of Providencia species isolated from wild-caught D. melanogaster. These pathogens are of particular interest as they have a range of virulence in fruit flies, and work in vivo suggests that differences in virulence could be partially attributable to differential susceptibility to AMPs. D. melanogaster cecropins are 40 amino acids long but vary at only 5 residues with largely conservative changes. We found that these changes could impact inhibitory concentrations by up to 8-fold against Providencia species. Our investigation focused on a single amino acid position due to the importance of a flexible "hinge" in cecropin function. We found that altering the identity of this amino acid alone greatly impacted antimicrobial activity, changing bacterial susceptibility up to 16-fold. Generally, Providencia species that are less virulent in vivo are more susceptible to cecropin AMPs in vitro. We also observed differences in the kinetics of permeabilization and bacterial killing between species, suggesting that peptide-membrane interactions were differently affected by single amino acid changes and that bacteria in this genus may vary in their membrane composition.

Dithiocarbamate-Based Sequence-Defined Oligomers as Promising Membrane-Disrupting Antibacterial Agents: Design, Activity, and Mechanism

The emerging prevalence of antimicrobial resistance demands cutting-edge therapeutic agents to treat bacterial infections. We present a synthetic strategy to construct sequence-defined oligomers (SDOs) by using dithiocarbamate (DTC). The antibacterial activity of the synthesized library of SDOs was studied using a Gram-positive B. subtilis and a Gram-negative E. coli. Among SDOs, Dec (with C10 aliphatic chain) was found to be the most promising antibacterial agent exhibiting a minimum inhibitory concentration (MIC) of 3 μg/mL against B. subtilis. Structure-activity relationship studies led to a 400-fold improvement in the MIC within the SDO library. The mode of action of the SDOs was elucidated on a model system, where bacterial membranes mimicking giant unilamellar vesicles (GUVs) were exposed to the SDOs. Membrane disruption and pore formation were found to be the key mechanisms through which SDOs act. In addition, scanning electron microscopy (SEM) and confocal laser scanning microscopy analysis of Dec-treated bacteria confirmed the loss of cell membrane integrity. Finally, the hemolysis assay with SDOs revealed their excellent selectivity toward bacterial cells. Taken together, we developed a modular platform for the synthesis of SDOs having promising antibacterial activity and superior selectivity toward bacteria, with the membrane disruption mode of action confirmed via studies on the model GUV system and SEM analysis.

Antimicrobial peptides selectively target malaria parasites by a cholesterol-dependent mechanism

Hundreds of thousands die annually from malaria caused by Plasmodium falciparum (Pf), with the emergence of drug-resistant parasites hindering eradication efforts. Antimicrobial peptides (AMPs) are known for their ability to disrupt pathogen membranes without targeting specific receptors, thereby reducing the chance of drug resistance. However, their effectiveness and the biophysical mechanisms by which they target the intracellular parasite remain unexplored. Here, by using native and synthetic AMPs, we discovered a selective mechanism that underlies the antimalarial activity. Remarkably, the AMPs exclusively interact with Pf-infected red blood cells, disrupting the cytoskeletal network and reaching the enclosed parasites with correlation to their activity. Moreover, we showed that the unique feature of reduced cholesterol content in the membrane of the infected host makes Pf-infected red blood cells susceptible to AMPs. Overall, this work highlights the Achilles' heel of malaria parasite and demonstrates the power of AMPs as potential antimalarial drugs with reduced risk of resistance.

CLEC3A-Derived Antimicrobial Peptides Reduce Staphylococcus aureus Bacterial Counts in an In Vivo Biomaterial-Associated Infection Mouse Model

Background/Objectives: Biomaterials are an essential part of healthcare for both diagnostic and therapeutic procedures. Although some biomaterials possess antimicrobial properties, introducing biomaterial into the body may lead to infections due to bacterial adhesion on their surfaces and still poses a major clinical problem. Peptides derived from the human cartilage-specific C-type lectin domain family 3 member A (CLEC3A) show a potent antimicrobial effect. In addition, coating titanium, a commonly used prosthetic material, with the CLEC3A-derived AMPs HT-47 and WRK-30 greatly reduces the number of adherent bacteria in vitro. The aim of this study was to evaluate the effectiveness of CLEC3A-derived peptides HT-47 and WRK-30 in reducing bacterial adhesion and mitigating infection in vivo in a murine biomaterial-associated infection model. Methods: To do so, an in vivo mouse infection model was used, where titanium plates-either uncoated or coated with chimeric CLEC3A-derived peptides TiBP-HT-47 and TiBP-WRK-30-were implanted subcutaneously into mice. This was followed by the introduction of Staphylococcus aureus bacterial cultures to induce a biomaterial-associated infection. After 24 h, the titanium plates, surrounding tissue, and mice blood samples were investigated. Results: CLEC3A-coated titanium plates lead to a significantly lower bacterial count than uncoated ones. Additionally, they prevent the infection from spreading to the surrounding tissue. Moreover, mice with CLEC3A-coated implants display lower IL-6 serum levels and therefore decreased systemic inflammation. Conclusions: In conclusion, in this biomaterial-associated infection mouse-model, CLEC3A-derived peptides show in vivo antimicrobial activity by reducing bacterial burden on biomaterial and wound tissue and decreasing systemic inflammation, making them promising candidates for clinical applications.

Integrating synthetic polypeptides with innovative material forming techniques for advanced biomedical applications

Polypeptides are highly valued in biomedical science for their biocompatibility and biodegradability, making them valuable in drug delivery, tissue engineering, and antibacterial dressing. The diverse design of polymer chains and self-assembly techniques allow different side chains and secondary structures, enhancing their biomedical potential. However, the traditional solid powder form of polypeptides presents challenges in skin applications, shipping, and recycling, limiting their practical utility. Recent advancements in material forming methods and polypeptide synthesis have produced biomaterials with uniform, distinct shapes, improving usability. This review outlines the progress in polypeptide synthesis and material-forming methods over the past decade. The main synthesis techniques include solid-phase synthesis and ring-opening polymerization of N-carboxyanhydrides while forming methods like electrospinning, 3D printing, and coating are explored. Integrating structural design with these methods is emphasized, leading to diverse polypeptide materials with unique shapes. The review also identifies research hotspots using VOSviewer software, which are visually presented in circular packing images. It further discusses emerging applications such as drug delivery, wound healing, and tissue engineering, emphasizing the crucial role of material shape in enhancing performance. The review concludes by exploring future trends in developing distinct polypeptide shapes for advanced biomedical applications, encouraging further research.

Interleaflet Translocation of Second-Harmonic-Generation-Active Dye Molecules in Phospholipid Bilayers with Transmembrane Pores

Second harmonic generation (SHG) measurements using SHG-active dye molecules have recently attracted attention as a method to detect the formation of pores in phospholipid bilayers. The bilayers, in which the dye molecules are embedded in the outer leaflet, exhibit a noncentrosymmetric structure, generating SHG signals. However, when pores form, these dye molecules translocate through the pores into the inner leaflet, leading to a more centrosymmetric structure and the subsequent loss of the SHG signals. A decrease in the SHG signals has been experimentally observed in membranes subjected to electrical stimuli. However, the characteristics of the interleaflet translocation of SHG-active dye molecules through pores remain unclear, hindering quantitative estimation of the membrane conditions, such as the pore size and density, based on the SHG signal reduction. In this study, we investigated the interleaflet translocation characteristics of Ap3, an SHG-active dye molecule, using molecular dynamics (MD) simulations and two-dimensional random-walk (RW) simulations. The MD simulations revealed that Ap3 molecules only translocate between the leaflets along the pore sidewalls. We determined the lateral diffusion coefficient of Ap3 within the membrane plane and its propensity for interleaflet movement at the pore wall. Based on these movement characteristics, the RW model successfully reproduced the characteristic time scale of the interleaflet translocation observed in the MD simulations. By varying the pore size and density in the RW simulations, we estimated that the characteristic time scale of interleaflet translocation depends on the -0.31 power of the pore radius and the -1.13 power of the pore density. Using these findings, we estimated the number of pores that probably formed in membranes during previous electroporation experiments. These results indicate the potential of optical measurement of the dye molecule movement for the indirect quantitative estimation of the pore size and number, which are challenging to measure optically.

Sulfonium-based polymethacrylamides for antimicrobial use: influence of the structure and composition

We are facing a shortage of new antibiotics to fight against increasingly resistant bacteria. As an alternative to conventional small molecule antibiotics, antimicrobial polymers (AMPs) have great potential. These polymers contain cationic and hydrophobic groups and disrupt bacterial cell membranes through a combination of electrostatic and hydrophobic interactions. While most examples focus on ammonium-based cations, sulfonium groups are recently emerging to broaden the scope of polymeric therapeutics. Here, main-chain sulfonium polymers exhibit good antimicrobial activity. In contrast, the potential of side-chain sulfonium polymers remains less explored with structure-activity relationships still being limited. To address this limitation, we thoroughly investigated key factors influencing antimicrobial activity in side-chain sulfonium-based AMPs. For this, we combined sulfonium cations with different hydrophobic (aliphatic/aromatic) and hydrophilic polyethylene glycol (PEG) groups to create a library of polymers with comparable chain lengths. For all compositions, we additionally examined the position of cationic and hydrophobic groups on the polymer backbone, i.e., we systematically compared same center and different center structures. Bactericidal tests against Gram-positive and Gram-negative bacteria suggest that same center polymers are more active than different center polymers of similar clog P. Ultimately, sulfonium-based AMPs show superior bactericidal activity and selectivity when compared to their quaternary ammonium cationic analogues.

The novel β-hairpin antimicrobial peptide D-G(RF)3 demonstrates exceptional antibacterial efficacy

The clinical application of most natural antimicrobial peptides (AMPs) is hindered by their lack of a synergistic combination of high antibacterial efficacy, low toxicity, and stability, necessitating frequent complex modifications that incur significant labor and economic costs. Therefore, it is imperative to optimize the antibacterial properties of AMPs using some simplified approach. In this study, we designed a library of β-hairpin AMPs with identical β-turn sequences (-D-Pro-Gly-) and varying repetition units (IR, FR, and WK). Ultimately, candidate peptide G(RF)3 exhibited high antibacterial activity and low toxicity; however, its stability was compromised. Moreover, we synthesized the new analogue D-G(RF)3 by D-type amino acid substitution of G(RF)3, and D-G(RF)3 demonstrated concurrent high antibacterial activity, low toxicity, and remarkable stability. Interestingly, both G(RF)3 and D-G(RF)3 exerted bactericidal effects by disrupting the bacterial membrane. However, D-G(RF)3 displayed superior antibiofilm activity with a faster bactericidal rate compared to G(RF)3 and also showed enhanced synergy with antibiotics. Furthermore, D-G(RF)3 exhibited potent in vivo bactericidal activity without inducing drug resistance and has the potential to be a novel antibiotic alternative or adjuvant.

Shigella infection is facilitated by interaction of human enteric α-defensin 5 with colonic epithelial receptor P2Y11

Human enteric α-defensin 5 (HD5) is an immune system peptide that acts as an important antimicrobial factor but is also known to promote pathogen infections by enhancing adhesion of the pathogens. The mechanistic basis of these conflicting functions is unknown. Here we show that HD5 induces abundant filopodial extensions in epithelial cells that capture Shigella, a major human enteroinvasive pathogen that is able to exploit these filopodia for invasion, revealing a mechanism for HD5-augmented bacterial invasion. Using multi-omics screening and in vitro, organoid, dynamic gut-on-chip and in vivo models, we identify the HD5 receptor as P2Y11, a purinergic receptor distributed apically on the luminal surface of the human colonic epithelium. Inhibitor screening identified cAMP-PKA signalling as the main pathway mediating the cytoskeleton-regulating activity of HD5. In illuminating this mechanism of Shigella invasion, our findings raise the possibility of alternative intervention strategies against HD5-augmented infections.

The Potential Effect of Endogenous Antimicrobial Peptides in Cancer Immunotherapy and Prevention

Antimicrobial peptides (AMPs) are crucial constituents of inherent immunity and serve as vital components of human host defense, playing a pivotal role in combating invading microbial pathogens. Beyond their antimicrobial functions, AMPs also exhibit various other biological activities including apoptosis induction, wound healing promotion, and immune modulation. These peptides are found in various exposed tissues or surfaces throughout the body, such as eyes, skin, mouth, ears, respiratory tract, lungs, digestive, and urinary system. Additionally, certain AMPs such as LL-37, HNP, and lactoferrin have shown potential as candidates for anticancer activity. Given the limited selectivity between normal and cancer cells exhibited by many current immunotherapeutic agents, the inherent properties of AMPs make them promising candidates for cancer treatment. Their abundance, bioavailability, safety profile, efficiency, and harmony with the host immune system position them as attractive tools in the fight against cancer. This review is aimed at exploring the potential anticancer properties of AMPs and elucidating their relationship with immunology and cancer immunotherapy.

Characterization of antimicrobial properties of TroH2A-29 peptide from golden pompano (Trachinotus ovatus)

Antimicrobial peptides (AMPs) are small, potent molecules that serve as a crucial first line of defense across a wide range of organisms, including fish. In this study, we investigated the antimicrobial properties of a novel peptide, spanning residues 52 to 80 of the full-length histone H2A protein, comprising a total of 29 amino acids. This peptide, designated as Histone H2A-29 (TroH2A-29), was derived from the golden pompano (Trachinotus ovatus) and evaluated for its activity against both Gram-positive bacteria, Lactococcus garvieae and Staphylococcus epidermidis, and Gram-negative bacteria, Vibrio alginolyticus and Vibrio harveyi. The expression of TroH2A in the intestines, liver, and gills of T. ovatus was significantly upregulated after bacterial infections with L. garvieae and V. harveyi. The highest expression levels were observed at 48 h post-infection in the intestines and at different time points in the liver and gills. TroH2A-29 exhibited a high hydrophobic ratio (51 %) and formed an α-helical structure, suggesting its potential as an antimicrobial agent. Notably, TroH2A-29 induced significant agglutination of all four bacterial species in the presence of Ca2⁺. TroH2A-29 demonstrated bactericidal effects against L. garvieae, V. harveyi, and V. alginolyticus, with a MIC50 of 60 μM. However, it showed no antibacterial activity against S. epidermidis. Transmission electron microscopy (TEM) revealed that TroH2A-29 caused morphological damage to the bacterial cells, including cell collapse in L. garvieae and shrinkage in V. alginolyticus and V. harveyi. No morphological changes were observed in S. epidermidis. Membrane permeability assays showed that TroH2A-29 increased membrane disruption in L. garvieae, V. harveyi, and V. alginolyticus, but had little effect on S. epidermidis. Additionally, TroH2A-29 caused membrane depolarization in all tested bacterial strains. These findings highlight the potential of TroH2A-29 as a novel antimicrobial peptide with selective bactericidal properties.

Secretory Production of Heterologous Antimicrobial Peptides in Corynebacterium glutamicum

Antimicrobial peptides (AMPs) are host defense peptides that act against a broad spectrum of microorganisms. AMPs are of high interest as medicinal products, antimicrobial coatings, and for controlling biofilm formation. Applications and research of many AMPs are still hampered by insufficient titers and lack of production platforms that can tolerate high titers of AMPs. Corynebacterium glutamicum is an excellent microbial host for protein secretion and has been barely explored as a host for AMP production. Here, we report the successful production and secretion of two AMPs (amounts of up to 130 mg/L for liquid chromatography peak I [LCI] and 54 mg/L for Psoriasin) by C. glutamicum with low amounts of secreted byproducts.

In silico antiviral effect assessment of some venom gland peptides from Odontobuthus doriae scorpion against SARS-CoV-2

SARS-CoV-2 is from the enveloped virus family responsible for the COVID-19 pandemic. No efficient drugs are currently available to treat infection explicitly caused by this virus. Therefore, searching for effective treatments for severe illness caused by SARS-CoV-2 is crucial. Scorpion venoms are significant sources of peptides with pharmaceutical potential, including antivirals. Although some studies have determined the antiviral effects of some scorpion peptides on other members of the Coronaviridae family, a few anti-SARS-CoV-2 effects of these peptides have been reported until now. This study assessed the antiviral effects of five predicted antimicrobial peptides with potential for antiviral activities from the Iranian yellow scorpion "Odontobuthus doriae" by computational methods. These peptides were selected from the cDNA library that our research team constructed. A 3D model of peptides was designed with I-TASSER. The models were refined using a 200 ns Molecular Dynamics (MD) simulation using Gromacs 2021.2 software. Refined models were Docked with the RBD domain of SARS-CoV-2 spike protein using HADDOCK software. The docking of human ACE2 peptide with the RBD domain was also assessed. The docked complexes (RBD-peptide and RBD-ACE2) were refined again by a 100 ns MD simulation and then analyzed. The results from molecular docking after molecular dynamics simulation showed that ODAMP2 and ODAMP5 after stabilizing analysis and according to MMPBSA results (with -59.24 kcal/mol and -51.82 kcal/mol, respectively) have a strong binding affinity to the RBD domain of COVID-19 spike protein compared to human ACE2 and some other studied components. Therefore, this peptide can be an excellent candidate for use as an agent to inhibit the RBD domain of SARS-COV2 virus in clinical studies for medicinal purposes after in vitro and in vivo laboratory evaluations.

Cliotide U1, a Novel Antimicrobial Peptide Isolated From Urtica Dioica Leaves

Aims

Antibiotic resistance is currently a major challenge to scientists. Thus, attempts have been made to develop new compounds with antimicrobial activity. In this research, a new antimicrobial peptide with antibacterial activity was isolated from the plant Urtica dioica.

Methods

A new antimicrobial peptide, named cliotide U1, was purified through precipitation with ammonium sulfate and reverse-phase high-performance liquid chromatography. In silico methods analyzed the physicochemical properties of cliotide U1. The properties of the peptide, including antibacterial activity, pH stability, heat stability, cytotoxicity, and hemolytic activity, were also examined.

Findings

The purified peptide was composed of 35 amino acids with a hydrophobicity ratio of 63% and a net charge of + 5. The antibacterial activity of cliotide U1 was observed against gram-negative and gram-positive bacteria with a minimum inhibitory concentration (MIC) of 1 to 4 µM. Cliotide U1 had less than 2% cytotoxic activity at the MIC range against the human embryonic kidney cell line 293 with no clear hemolytic activity. The stability of cliotide U1 was preserved at various temperatures (10-60°C) and pH (6-9).

Conclusion

Our results demonstrated that cliotide U1 had potent antibacterial potential against gram-negative and gram-positive bacteria. Considering its properties, cliotide U1 can be introduced as a novel antibacterial candidate for expanding new therapeutic drugs.

Antimicrobial peptide LL37 is potent against non-growing Escherichia coli cells despite a slower action rate

Antimicrobial peptides (AMPs) have long been considered as potential agents against non-growing, dormant cells due to their membrane-targeted action, which is largely independent of the cell's growth state. However, the relationship between the action of AMPs and the physiological state of their target cells has been unclear, with recent reports offering conflicting views on the efficacy of AMPs against bacteria in a stationary phase. In this study, we employ single-cell approaches combined with population-level experiments to examine the action of human LL37 peptides against Escherichia coli cells in different growth phases. Time-lapse, single-cell data from our experiments reveal that LL37 peptides act faster on large, dividing cells than on small, newborn cells. We extend this investigation to non-growing E. coli cells in a stationary phase, where we observe that the action of LL37 peptides is slower on non-growing cells compared to exponentially growing cells. This slower action rate is, however, not mirrored in the minimum bactericidal concentration (MBC) measurements. Notably, we find that the MBC for non-growing cells is lower than for exponentially growing cells, indicating that, given sufficient time, LL37 peptides exhibit strong potency against non-growing cells. We propose that the enhanced potency of LL37 peptides against non-growing cells, despite their slower action, can be attributed to continuous absorption of AMPs on the cell membrane over time.

IMPORTANCE

Antibiotic treatments can fail because of the regrowth of a bacterial subpopulation that resumes proliferation once the treatment ceases. This resurgence is primarily driven by non-growing, dormant bacterial cells that withstand the action of antibiotics without developing resistance. In this study, we explore the potency of the human antimicrobial peptide LL37 against non-growing Escherichia coli cells. Our findings reveal that despite a slower initial action, LL37 peptides, given sufficient time, demonstrate strong efficacy against non-growing cells. These insights suggest a potential role of antimicrobial peptides in combating persistent bacterial infections by targeting the non-growing cells.

Amphibian-Derived Peptides as Natural Inhibitors of SARS-CoV-2 Main Protease (Mpro): A Combined In Vitro and In Silico Approach

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has highlighted the urgent need for novel therapeutic agents targeting viral enzymes such as the main protease (Mpro), which plays a crucial role in viral replication. In this study, we investigate the inhibitory potential of 23 peptides isolated from the skin of amphibians belonging to the Hylidae and Leptodactylidae families against SARS-CoV-2 Mpro. Five peptides demonstrated significant inhibition using a colorimetric Mpro inhibition assay, with IC50 values ranging from 41 to 203 µM. Among these, peptides Hp-1081 and Hp-1971, derived from Boana pulchella, exhibited the strongest activity, comparable to the natural Mpro inhibitor quercetin. The binding mechanism of the most potent peptide, Hp-1081, was further investigated through docking and molecular dynamics (MDs) simulations and energetic analysis, which revealed key Mpro residues involved in the binding process. Moreover, because SARS-CoV-2 infection can induce ROS overproduction, the antioxidant activity of Hp-1081 was assessed, reaching 48% of DPPH radical scavenging activity at 100 µM. The most potent peptides also showed no toxicity against human erythrocytes and Artemia salina. This study provides insight into the antiviral potential of amphibian-derived peptides and highlights their applicability as natural templates for drug development targeting coronaviruses.