Assembly of cationic and amphiphilic β-sheet FKF tripeptide confers antibacterial activity

Engineered Assemblies from Constitutionally Isomeric Peptides Modulate Antimicrobial Activity

Antimicrobial peptides (AMPs) are a class of peptides consisting of cationic amino acid residues and a hydrophobic segment, which have been used as an alternative to antibiotics in treating multidrug-resistant bacteria. However, the relationship among the molecular design, assembled structures, and resultant efficacy remains elusive. Herein, we report a class of constitutionally isomeric AMPs assembled into filaments with similar dimensions. Spectroscopic characterizations demonstrated that subtle changes in the position of amino acids led to dramatic variations in molecular packing and surface charges, which were verified by molecular dynamics simulations. In vitro antibacterial assays showed that all AMPs exerted antibacterial activity against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), but the efficacy was dependent on the molecular design. Given the good biocompatibility to eukaryotic cells, these AMPs could be potentially used as antibacterial agents. We believe that this finding provides an avenue to tune the bioactivity of AMPs by rational molecular design.

Electrospinning of Self-Assembling Oligopeptides into Nanofiber Mats: The Impact of Peptide Composition and End Groups

Low-molecular-weight oligopeptides can be electrospun into nanofiber mats. However, the mechanism underlying their electrospinnability is not well-understood. In this study, we used solid-phase peptide synthesis to produce the oligopeptide FFKK, to which the aromatic end-capping groups naphthalene, pyrene, and tetraphenylporphyrin were attached. Nuclear magnetic resonance, circular dichroism, and electrospray ionization mass spectrometry were used to characterize the oligopeptide structures. We investigated the effect of end-caps and oligopeptide concentration on their self-assembly as well as on their electrospinnability in fluorinated solvents. All oligopeptides with aromatic end-caps were amenable to electrospinning. Attenuated total reflectance Fourier transform infrared spectroscopy and microrheology results support the hypothesis that at sufficiently high concentrations, the self-assembled structures interact strongly, which facilitates electrospinning. Moreover, the results from this fundamental study can be extended to nonpeptidic small molecules possessing strong intermolecular interactions.

Ultrashort Peptide Hydrogels Biomaterials with Potent Antibacterial Activity

For the past few decades, ultrashort peptide hydrogels have been at the forefront of biomaterials due to their unique properties like biocompatibility, tunable mechanical properties, and potent antibacterial activity. These ultrashort peptides self-assemble into a hydrogel matrix with nanofibrous networks. In this minireview, we have explored the design and self-assembly of these ultrashort peptide hydrogels by focusing on their antibacterial properties. Cationic and hydrophobic residues are incorporated to engineer the peptides, facilitating interaction with bacterial membranes and leading to membrane disruption and cell death. The hydrogels exhibit broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria. Overall, this minireview highlights the potential of ultrashort peptide hydrogels as versatile and practical antibacterial biomaterials, providing a novel approach to combating bacterial infections and addressing the growing challenge of antibiotic resistance.

Identification and Functional Analysis of Novel SNPs in Enterocin Genes of Enterococcus faecium GHB21

This study investigates the functional and structural impact of single nucleotide polymorphisms (SNPs) in the enterocin and associated immunity genes of Enterococcus faecium GHB21, a strain known for producing potent antimicrobial peptides. Enterocins, most of them classified as class IIa bacteriocins, exhibit strong activity against pathogens such as Listeria monocytogenes, making them promising candidates for food preservation and therapeutic interventions. Using cloning, sequencing, and bioinformatics tools, we analyzed key enterocin genes (entA, entB and entP) and their associated immunity genes (entAi and entPi). Two novel SNPs were identified that result in amino acid substitutions: G15N in pre-enterocin P (EntP), located within the leader sequence, and V36I in the EntPi immunity protein. Additionally, the V9I mutation within the conserved YGNGV motif of the mature EntP peptide and the G48S mutation in the EntAi immunity protein were analyzed. Protein Variation Effect Analyzer classified all mutations as neutral, indicating minimal disruption to protein function. DynaMut analysis revealed that V9I stabilizes EntP but slightly reduces its flexibility, potentially influencing its interaction with target bacteria. Despite these mutations, the enterocins retained critical structural features, including disulfide bonds and β-sheet arrangements, ensuring their antimicrobial efficacy. These findings underscore the structural resilience of enterocins, supporting their application in food safety and in combating multidrug-resistant pathogens.

Stimuli-responsive mesoporous silica nanoplatforms for smart antibacterial therapies: From single to combination strategies

The demand for new antibacterial therapies is urgent and crucial in the clinical setting because of the growing degree of antibiotic resistance and the limits of conventional antibacterial therapies. Stimuli- responsive nanoplatforms, are sensitive to endogenous or exogenous stimulus (pH, temperature, light, and magnetic fields, etc.) which activate cargo release locally and on-demand, hold great potential in developing next generation personalized precision medicine. For instance, pH-sensitive nanoplatforms can selectively release antibacterial agents in the acidic environment of infection sites. To achieve the stimuli-responsive delivery, mesoporous silica nanoplatforms (MSNs) have demonstrated as prospective candidates for efficient cargo loading and controlled release through strategies such as tunable pore engineering, versatile surface modification/coating, and tailored framework composition. Furthermore, aiming for more precise delivery of MSNs, current research interests are increasingly shifting from single-stimuli antibacterial strategy to integrated strategy that combine multiple-stimulus. In this review, we briefly discuss the microenvironment of bacterial infections and provide a comprehensive summary of current stimuli-responsive strategies, and associated materials design principles of stimuli-responsive mesoporous silica-based smart nanoplatforms (SRMSNs). Additionally, integrative antibacterial strategies with synergistic effects, combining chemodynamic, photodynamic, photothermal, sonodynamic and gas therapies, have also been elaborated. Present research advances and limitations of SRMSNs-based antibacterial therapies, such as limited biodegradability and potential cytotoxicity, have been overviewed with future outlooks presented. This review aims to inspire and guide future research in developing novel antibacterial strategies with integrative solutions.

Self-assembling peptide with dual function of cell penetration and antibacterial as a nano weapon to combat intracellular bacteria

Intracellular bacterial infections and antimicrobial resistance are threatening global public health systems. Antimicrobial peptides are a potential solution to combat bacterial resistance, but the design of self-assembled nanopeptides with dual functions of cell penetration and antibacterial properties to combat intracellular bacteria remains a challenge. Here, we propose a strategy to develop self-assembled nanopeptides with dual functions through the chimerization of self-assembled core, hydrophobic motif, and cell-permeable unit. The optimal nanopeptides, F3FT and N3FT, exhibited potent antibacterial activity and excellent biocompatibility. Crucially, F3FT and N3FT are able to efficiently penetrate cells and eliminate intracellular bacteria and sniping inflammation. Moreover, F3FT and N3FT kill bacteria mainly by disrupting bacterial cell membranes and inducing excessive accumulation of reactive oxygen species. F3FT and N3FT have exhibited good safety and potent therapeutic potential in vivo. This scheme of constructing nanopeptides through multifunctional domains design provides a paradigm for dealing with escalating of intracellular bacteria and antimicrobial resistance.

Multifunctional cyclic biomimetic peptides: Self-assembling nanotubes for effective treatment of sepsis

Antibiotic abuse has led to an increasingly serious risk of antimicrobial resistance, developing alternative antimicrobials to combat this alarming issue is urgently needed. Rhesus theta defensin-1 (RTD-1) is a theta-defensin contributing to broad-spectrum bactericidal activity via the mechanisms of membrane perturbation. Intriguingly, human defensin-6 (HD6), an enteric defensin secreted by Paneth cells without direct bactericidal effect, could self-assembled into fibrous networks to trap enteric pathogens for assistance of innate immunity. The direct bactericidal action of RTD-1 and the bacterial trapping of HD6 inspire a promising antimicrobial paradigm for unique antibacterial strategies. In this study, we utilized the principle of alternating arrangement of D- and L-amino acids in cyclic peptides, which endows them with the potential to self-assemble into nanotubes, mimic the antimicrobial processes of RTD-1 and HD6. We designed and synthesized five cyclic biomimetic peptides (CBPs), among these biomimetics, CBP-4, which possessed a nanotube-like structure, demonstrated the ability to directly and rapidly disrupt the cell membranes of Gram-positive S. aureus and MRSA, while also targeting the surfaces of Gram-negative E. coil using its nanofibrous network to capture bacteria, preventing invasion and migration, and indirectly killing the bacteria. Moreover, CBP-4 eliminated pathogens, inhibited excessive inflammatory responses caused by infections, and maintained immune system homeostasis in septic mice. By fully emulating the antimicrobial mechanisms of both RTD-1 and HD6, CBP-4 showed promising potential for anti-infectious therapies.

Peptide-Based Biomaterials for Combatting Infections and Improving Drug Delivery

This review explores the potential of peptide-based biomaterials to enhance biomedical applications through self-assembly, biological responsiveness, and selective targeting. Peptides are presented as versatile agents for antimicrobial activity and drug delivery, with recent approaches incorporating antimicrobial peptides into self-assembling systems to improve effectiveness and reduce resistance. The review also covers peptide-based nanocarriers for cancer drug delivery, highlighting their improved stability, targeted delivery, and reduced side effects. The focus of this work is on the bioactive properties of peptides, particularly in infection control and drug delivery, rather than on their structural design or material characteristics. Additionally, it examines the role of peptidomimetics in broadening biomaterial applications and enhancing resistance to enzymatic degradation. Finally, the review discusses the commercial prospects and challenges of translating peptide biomaterials into clinical applications.

Self-assembly of heterochiral, aliphatic dipeptides with Leu

This work describes the self-assembly behavior of heterochiral, aliphatic dipeptides, l-Leu-d-Xaa (Xaa = Ala, Val, Ile, Leu), in green solvents such as acetonitrile (MeCN) and buffered water at neutral pH. Interestingly, water plays a structuring role because at 1% v/v, it enables dipeptide self-assembly in MeCN to yield organogels, which then undergo transition towards crystals. Other organic solvents and oils were tested for gelation, and metastable gels were formed in tetrahydrofuran, although at high peptide concentration (80 mM). Single-crystal X-ray diffraction revealed the dipeptides' supramolecular packing modes in amphipathic layers, as opposed to water channels reported for the homochiral Leu-Leu, or hydrophobic columns reported for homochiral Leu-Val and Leu-Ile.

Martinoid: the peptoid martini force field

Many exciting innovations have been made in the development of assembling peptoid materials. Typically, these have utilised large oligomeric sequences, though elsewhere the study of peptide self-assembly has yielded numerous examples of assemblers below 6-8 residues in length, evidencing that minimal peptoid assemblers are not only feasible but expected. A productive means of discovering such materials is through the application of in silico screening methods, which often benefit from the use of coarse-grained molecular dynamics (CG-MD) simulations. At the current level of development, CG models for peptoids are insufficient and we have been motivated to develop a Martini forcefield compatible peptoid model. A dual bottom-up and top-down parameterisation approach has been adopted, in keeping with the Martini parameterisation methodology, targeting the reproduction of atomistic MD dynamics and trends in experimentally obtained log D7.4 partition coefficients, respectively. This work has yielded valuable insights into the practicalities of parameterising peptoid monomers. Additionally, we demonstrate that our model can reproduce the experimental observations of two very different peptoid assembly systems, namely peptoid nanosheets and minimal tripeptoid assembly. Further we can simulate the peptoid helix secondary structure relevant for antimicrobial sequences. To be of maximum usefulness to the peptoid research community, we have developed freely available code to generate all requisite simulation files for the application of this model with Gromacs MD software.

Minimal Peptoid Dynamics Inform Self-Assembly Propensity

Peptoids are structural isomers of natural peptides, with side chain attachment at the amide nitrogen, conferring this class of compounds with the ability to access both cis and trans ω torsions as well as an increased diversity of ψ/φ states with respect to peptides. Sampling within these dimensions is controlled through side chain selection, and an expansive set of viable peptoid residues exists. It has been shown recently that "minimal" di- and tripeptoids with aromatic side chains can self-assemble into highly ordered structures, with size and morphological definition varying as a function of sequence pattern (e.g., XFF and FXF, where X = a nonaromatic peptoid monomer). Aromatic groups, such as phenylalanine, are regularly used in the design of minimal peptide assemblers. In recognition of this, and to draw parallels between these compounds classes, we have developed a series of descriptors for intramolecular dynamics of aromatic side chains to discern whether these dynamics, in a preassembly condition, can be related to experimentally observed nanoscale assemblies. To do this, we have built on the atomistic peptoid force field reported by Weiser and Santiso (CGenFF-WS) through the rigorous fitting of partial charges and the collation of Charmm General Force Field (CGenFF) parameters relevant to these systems. Our study finds that the intramolecular dynamics of side chains, for a given sequence, is dependent on the specific combination of backbone ω torsions and that homogeneity of sampling across these states correlates well with the experimentally observed ability to assemble into nanomorphologies with long-range order. Sequence patterning is also shown to affect sampling, in a manner consistent for both tripeptoids and tripeptides. Additionally, sampling similarities between the nanofiber forming tripeptoid, Nf-Nke-Nf in the cc state, and the nanotube forming dipeptide FF, highlight a structural motif which may be relevant to the emergence of extended linear assemblies. To assess these properties, a variety of computational approaches have been employed.

Peptide-containing nanoformulations: Skin barrier penetration and activity contribution

Transdermal drug delivery presents a less invasive pathway, circumventing the need to pass through the gastrointestinal tract and liver, thereby reducing drug breakdown, initial metabolism, and gastrointestinal discomfort. Nevertheless, the unique composition and dense structure of the stratum corneum present a significant barrier to transdermal delivery. This article presents an overview of the current developments in peptides and nanotechnology to address this challenge. Initially, we sum up peptide-containing nanoformulations for transdermal drug delivery, examining them through the lenses of both inorganic and organic materials. Particular emphasis is placed on the diverse roles that peptides play within these nanoformulations, including conferring functionality upon nanocarriers and enhancing the biological efficacy of drugs. Subsequently, we summarize innovative strategies for enhancing skin penetration, categorizing them into passive and active approaches. Lastly, we discuss the therapeutic potential of peptide-containing nanoformulations in addressing a range of diseases, drawing insights from the biological activities and functions of peptides. Furthermore, the challenges hindering clinical translation are also discussed, providing valuable insights for future advancements in transdermal drug delivery.

Self-assembling tripeptide forming water-bound channels and hydrogels

D-Ser(tBu)-L-Phe-L-Trp is described as a self-assembling tripeptide that yields nanofibrillar hydrogels at physiological conditions (phosphate buffer at pH 7.4). The peptide is characterized by several spectroscopic methods, such as circular dichroism and fluorescence, oscillatory rheometry, and transmission electron microscopy. Single-crystal X-ray diffraction reveals supramolecular packing into water-bound channels and allows the visualization of the intermolecular interactions holding together peptide stacks.

Peptide Supramolecular Hydrogels with Sustained Release Ability for Combating Multidrug-Resistant Bacteria

Chronic wound infection caused by multidrug-resistant bacteria is a major threat globally, leading to high mortality rates and a considerable economic burden. To address it, an innovative supramolecular nanofiber hydrogel (Hydrogel-RL) harboring antimicrobial peptides was developed based on the novel arginine end-tagging peptide (Pep 6) from our recent study, triggering cross-linking. In vitro results demonstrated that Hydrogel-RL can sustain the release of Pep 6 up to 120 h profiles, which is biocompatible and exhibits superior activity for methicillin-resistant Staphylococcus aureus (MRSA) biofilm inhibition and elimination. A single treatment of supramolecular Hydrogel-RL on an MRSA skin infection model revealed formidable antimicrobial activity and therapeutic effects in vivo. In the chronic wound infection model, Hydrogel-RL promoted mouse skin cell proliferation, reduced inflammation, accelerated re-epithelialization, and regulated muscle and collagen fiber formation, rapidly healing full-thickness skin wounds. To show its vehicle property for wound infection combined therapy, etamsylate, an antihemorrhagic drug, was loaded into the porous network of Hydrogel-RL, which demonstrated improved hemostatic activity. Collectively, Hydrogel-RL is a promising clinical candidate agent for functional supramolecular biomaterials designed for combating multidrug-resistant bacteria and rescuing stalled healing in chronic wound infections.

Recent Advances in Antimicrobial Peptide Hydrogels

Advances in the number and type of available biomaterials have improved medical devices such as catheters, stents, pacemakers, prosthetic joints, and orthopedic devices. The introduction of a foreign material into the body comes with a risk of microbial colonization and subsequent infection. Infections of surgically implanted devices often lead to device failure, which leads to increased patient morbidity and mortality. The overuse and improper use of antimicrobials has led to an alarming rise and spread of drug-resistant infections. To overcome the problem of drug-resistant infections, novel antimicrobial biomaterials are increasingly being researched and developed. Hydrogels are a class of 3D biomaterials consisting of a hydrated polymer network with tunable functionality. As hydrogels are customizable, many different antimicrobial agents, such as inorganic molecules, metals, and antibiotics have been incorporated or tethered to them. Due to the increased prevalence of antibiotic resistance, antimicrobial peptides (AMPs) are being increasingly explored as alternative agents. AMP-tethered hydrogels are being increasingly examined for antimicrobial properties and practical applications, such as wound-healing. Here, we provide a recent update, from the last 5 years of innovations and discoveries made in the development of photopolymerizable, self-assembling, and AMP-releasing hydrogels.

Effect of number of lysine motifs on the bactericidal and hemolytic activity of short cationic antimicrobial peptides

Antimicrobial peptides (AMPs) are vital components of the nonspecific immune system that represent a promising broad-spectrum alternative to conventional antibiotics. Several short cationic antimicrobial peptides show highly effective antibacterial activity and low hemolytic activity, which are based on the action of a few critical amino acids, such as phenylalanine (F) and lysine (K). Previous studies have reported that Fmoc-based phenylalanine peptides possess appreciable antibacterial potency against Gram-positive bacteria, but their ability to kill Gram-negative bacteria was suboptimal. In this study, we designed and prepared a series of Fmoc-K_nF peptide (n = 1-3) series by adding lysine motifs to strengthen their broad-spectrum antibacterial activity. The effect was investigated that the amount of lysine in Fmoc-F peptides on their antibacterial properties and hemolytic activities. Our results showed that the Fmoc-KKF peptide holds the strongest antimicrobial activity against both Gram-positive and negative bacteria among all designed peptides, as well as low hemolytic activity. These results provide support for the general strategy of enhancing the broad-spectrum antibacterial activity of AMPs through increased lysine content.

Hybrid Hydrogels of FKF-Peptide Assemblies and Gelatin for Sustained Antimicrobial Activity

The growing resistance of pathogenic bacteria to conventional antibiotics promotes the development of new antimicrobial agents, including peptides. Hydrogels composed of antimicrobial peptides (AMPs) may be applied as topical treatments for skin infection and wound regeneration. The unique antimicrobial and ultrashort-peptide FKF (Phe-Lys-Phe) was recently demonstrated to form bactericidal hydrogels. Here, we sought to improve the cyto-biocompatibility of FKF by combining FKF hydrogels with gelatin. Homogeneous hybrid hydrogels of FKF:gelatin were developed based on a series of self-assembly steps that involved mixing solutions of the two components with no covalent cross-linkers. The hydrogels were characterized for their structural features, dissolution, cyto-biocompatibility, and antibacterial properties. These hybrid hydrogels first release the antibacterial FKF assemblies, leaving the gelatinous fraction of the hydrogel to serve as a scaffold for tissue regeneration. Sponges of these hybrid hydrogels, obtained by lyophilization and rehydrated prior to application, exhibited enhanced antimicrobial activity compared to the hydrogels' formulations.

Design strategies for adhesive hydrogels with natural antibacterial agents as wound dressings: Status and trends

The wound healing process is usually susceptible to different bacterial infections due to the complex physiological environment, which significantly impairs wound healing. The topical application of antibiotics is not desirable for wound healing because the excessive use of antibiotics might cause bacteria to develop resistance and even the production of super bacteria, posing significant harm to human well-being. Wound dressings based on adhesive, biocompatible, and multi-functional hydrogels with natural antibacterial agents have been widely recognized as effective wound treatments. Hydrogels, which are three-dimensional (3D) polymer networks cross-linked through physical interactions or covalent bonds, are promising for topical antibacterial applications because of their excellent adhesion, antibacterial properties, and biocompatibility. To further improve the healing performance of hydrogels, various modification methods have been developed with superior biocompatibility, antibacterial activity, mechanical properties, and wound repair capabilities. This review summarizes hundreds of typical studies on various ingredients, preparation methods, antibacterial mechanisms, and internal antibacterial factors to understand adhesive hydrogels with natural antibacterial agents for wound dressings. Additionally, we provide prospects for adhesive and antibacterial hydrogels in biomedical applications and clinical research.

Mechanical Force Induced Self-Assembly of Chinese Herbal Hydrogel with Synergistic Effects of Antibacterial Activity and Immune Regulation for Wound Healing

Skin wounds, especially infected chronic wounds, have attracted worldwide attention due to the high prevalence and poor treatment outcomes. Hydrogel dressings with antibacterial ability and immune regulation property are urgently required. Herein, inspired by the grinding treatment of traditional Chinese medicine, mechanical force is introduced to promote the effective molecular collision and accelerate the self-assembly of chitosan (CS) and puerarin (PUE) for fabricating Chinese-herb-based hydrogels. The antibacterial rate of CS@PUE (C@P) hydrogel is more than 95%, and the wound closed rate is twice that of the control group. Interestingly, the rational design of C@P hydrogels with different PUE ratios enables a refined control over hydrogel formation, nanofiber appearance, viscoelastic, physicochemical, and biological properties. The extraordinary antibacterial ability of C@P hydrogels may originate from the nanofiber structure and the improved zeta potential on account of the orientation of amino groups in CS . Thus, the synergistically antibacterial and immune regulation properties of C@P hydrogels kill bacteria and relieve inflammation in the wound bed, ensuring the anti-infection effect, and boosting wound healing. In addition to providing a universal mechanosynthesis of PUE-based hydrogel for wound healing, this finding is expected to increase the attention paid to Chinese herbal medicines in the construction of biomaterials.

Nanomaterials in Skin Regeneration and Rejuvenation

Skin is the external part of the human body; thus, it is exposed to outer stimuli leading to injuries and damage, due to being the tissue mostly affected by wounds and aging that compromise its protective function. The recent extension of the average lifespan raises the interest in products capable of counteracting skin related health conditions. However, the skin barrier is not easy to permeate and could be influenced by different factors. In the last decades an innovative pharmacotherapeutic approach has been possible thanks to the advent of nanomedicine. Nanodevices can represent an appropriate formulation to enhance the passive penetration, modulate drug solubility and increase the thermodynamic activity of drugs. Here, we summarize the recent nanotechnological approaches to maintain and replace skin homeostasis, with particular attention to nanomaterials applications on wound healing, regeneration and rejuvenation of skin tissue. The different nanomaterials as nanofibers, hydrogels, nanosuspensions, and nanoparticles are described and in particular we highlight their main chemical features that are useful in drug delivery and tissue regeneration.

Challenge in the Discovery of New Drugs: Antimicrobial Peptides against WHO-List of Critical and High-Priority Bacteria

Bacterial resistance has intensified in recent years due to the uncontrolled use of conventional drugs, and new bacterial strains with multiple resistance have been reported. This problem may be solved by using antimicrobial peptides (AMPs), which fulfill their bactericidal activity without developing much bacterial resistance. The rapid interaction between AMPs and the bacterial cell membrane means that the bacteria cannot easily develop resistance mechanisms. In addition, various drugs for clinical use have lost their effect as a conventional treatment; however, the synergistic effect of AMPs with these drugs would help to reactivate and enhance antimicrobial activity. Their efficiency against multi-resistant and extensively resistant bacteria has positioned them as promising molecules to replace or improve conventional drugs. In this review, we examined the importance of antimicrobial peptides and their successful activity against critical and high-priority bacteria published in the WHO list.