Antimicrobial activity of histidine-rich peptides is dependent on acidic conditions

Cholesterol-terminated cationic lipidated oligomers (CLOs) as a new class of antifungals

Infections caused by fungal pathogens are a global health problem, and have created an urgent need for new antimicrobial strategies. This report details the synthesis of lipidated 2-vinyl-4,4-dimethyl-5-oxazolone (VDM) oligomers via an optimized Cu(0)-mediated reversible-deactivation radical polymerization (RDRP) approach. Cholesterol-Br was used as an initiator to synthesize a library of oligo-VDM (degree of polymerisation = 5, 10, 15, 20, and 25), with an α-terminal cholesterol group. Subsequent ring-opening of the pendant oxazolone group with various functional amines [i.e., 2-(2-aminoethyl)-1,3-di-Boc-guanidine (BG), 1-(3-aminopropyl)imidazole (IMID), N-Boc-ethylenediamine (BEDA), or N,N-dimethylethylenediamine (DMEN)] yielded an 11 functional cationic lipidated oligomer (CLOs) library, which comprised different cationic elements with the same terminal lipid cholesterol element. These CLOs exhibited greater activity against all tested fungal pathogens (Candida albicans, Cryptococcus neoformans, Candida tropicalis, Candida glabrata, Cryptococcus deuterogattii, and Candida auris), compared to the bacterial pathogens (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa or methicillin-resistant Staphylococcus aureus [MRSA]). Specifically, the DMEN and BEDA (after deprotection) series exhibited superior antifungal activities 4-16 times greater [determined by the minimum inhibitory concentration (MIC) in μg mL-1] than the clinically relevant antifungal fluconazole. Two 'hit' CLOs (Chol-DMEN-25 and Chol-BEDA-10) were identified, which inhibited both single sp. (C. albicans, C. tropicalis, C. neoformans, or C. gattii) and dual sp. (C. albicans and C. tropicalis) biofilm formation, and were able to attenuate mature biofilms, with a >50% mature biofilm biomass reduction at 128 μg mL-1. Co-delivery of fluconazole with two 'hit' CLOs demonstrated additive and synergistic effects on the aforementioned single-species and dual-species fungi biofilms, with a synergy score (SS) ranging from ∼3 to 15 and most synergistic area score (MSAS) ∼13-29 (by a Bliss independence model). The mechanistic studies (PI assay and nucleic acid release assay) revealed that these CLOs disrupted the integrity of fungal cell membranes. These results demonstrate that cholesterol terminated CLOs are potential antifungal candidates.

A Review of Antimicrobial Peptides: Structure, Mechanism of Action, and Molecular Optimization Strategies

Antimicrobial peptides (AMPs) are bioactive macromolecules that exhibit antibacterial, antiviral, and immunomodulatory functions. They come from a wide range of sources and are found in all forms of life, from bacteria to plants, vertebrates, and invertebrates, and play an important role in controlling the spread of pathogens, promoting wound healing and treating tumors. Consequently, AMPs have emerged as promising alternatives to next-generation antibiotics. With advancements in systems biology and synthetic biology technologies, it has become possible to synthesize AMPs artificially. We can better understand their functional activities for further modification and development by investigating the mechanism of action underlying their antimicrobial properties. This review focuses on the structural aspects of AMPs while highlighting their significance for biological activity. Furthermore, it elucidates the membrane targeting mechanism and intracellular targets of these peptides while summarizing molecular modification approaches aimed at enhancing their antibacterial efficacy. Finally, this article outlines future challenges in the functional development of AMPs along with proposed strategies to overcome them.

Specific interaction between the DSPHTELP peptide and various functional groups

M13 bacteriophages serve as a versatile foundation for nanobiotechnology due to their unique biological and chemical properties. The polypeptides that comprise their coat proteins, specifically pVIII, can be precisely tailored through genetic engineering. This enables the customized integration of various functional elements through specific interactions, leading to the development of innovative hybrid materials for applications such as energy storage, biosensing, and catalysis. Notably, a certain genetically engineered M13 bacteriophage variant, referred to as DSPH, features a pVIII with a repeating DSPHTELP peptide sequence. This sequence facilitates specific adhesion to single-walled carbon nanotubes (SWCNTs), primarily through π-π and hydrophobic interactions, though the exact mechanism remains unconfirmed. In this study, we synthesized the DSPHTELP peptide (an 8-mer peptide) and analyzed its interaction forces with different functional groups across various pH levels using surface forces apparatus (SFA). Our findings indicate that the 8-mer peptide binds most strongly to CH3 groups (Wad = 13.74 ± 1.04 mJ m-2 at pH 3.0), suggesting that hydrophobic interactions are indeed the predominant mechanism. These insights offer both quantitative and qualitative understanding of the molecular interaction mechanisms of the 8-mer peptide and clarify the basis of its specific interaction with SWCNTs through the DSPHTELP M13 bacteriophage.

Zn(II) and Cu(II) Coordination Enhances the Antimicrobial Activity of Piscidin 3, but Not That of Piscidins 1 and 2

Piscidins, antimicrobial peptides isolated from fish, are potent against a variety of human pathogens; they show minimum inhibitory concentration values comparable to those of commercially used antimicrobials. Piscidins 1 and 2 are generally more effective than piscidin 3 when applied alone; the contrary is observed for their metal complexes: Zn(II) and Cu(II) coordination does not enhance the efficacy of piscidins 1 and 2, while a moderate enhancement is observed for piscidin 3. All three piscidins bind Cu(II) in a so-called albumin-like binding mode, while for Zn(II) complexes, two coordination modes are observed: piscidins 1 and 2 bind Zn(II) by imidazole nitrogens from His4, His11, and His17 side chains; piscidin 3 coordinates Zn(II) by His3, His4, and His11 imidazole nitrogens and additionally supports the interaction, formed by carbonyl oxygen from His4. Most likely, the high antimicrobial activity of piscidin complexes is due to neither the stability of their complexes nor the change in their secondary structure. Copper(II) complexes with piscidins 1 and 2 can form hydroxyl radicals, which could be responsible for the antimicrobial membrane damaging activity of these complexes. Clearly, a different mechanism (most likely an intercellular targeted one) is observed for piscidin 3 metal complexes; in most cases, the coordination of Cu(II) and Zn(II) enhances the antimicrobial potency of piscidin 3, showing that not only piscidin 3 alone but also its metal complexes have a different mode of action than piscidins 1 and 2.

Antibacterial and Hemolytic Activity of Antimicrobial Hydrogels Utilizing Immobilized Antimicrobial Peptides

Antimicrobial peptides (AMPs) are viewed as potential compounds for the treatment of bacterial infections. Nevertheless, the successful translation of AMPs into clinical applications has been impeded primarily due to their low stability in biological environments and potential toxicological concerns at higher concentrations. The covalent attachment of AMPs to a material's surface has been sought to improve their stability. However, it is still an open question what is required to best perform such an attachment and the role of the support. In this work, six different AMPs were covalently attached to a long-ranged ordered amphiphilic hydrogel, with their antibacterial efficacy evaluated and compared to their performance when free in solution. Among the tested AMPs were four different versions of synthetic end-tagged AMPs where the sequence was altered to change the cationic residue as well as to vary the degree of hydrophobicity. Two previously well-studied AMPs, Piscidin 1 and Omiganan, were also included as comparisons. The antibacterial efficacy against Staphylococcus aureus remained largely consistent between free AMPs and those attached to surfaces. However, the activity pattern against Pseudomonas aeruginosa on hydrogel surfaces displayed a marked contrast to that observed in the solution. Additionally, all the AMPs showed varying degrees of hemolytic activity when in solution. This activity was entirely diminished, and all the AMPs were non-hemolytic when attached to the hydrogels.

Combination of a pH-responsive peptide amphiphile and a conventional antibiotic in treating Gram-negative bacteria

BACKGROUND

Clinical treatments ofgastric infections using antibiotics suffer from the undesired killing of commensal bacteria and emergence of antibiotic resistance. It is desirable to develop pH-responsive antimicrobial peptides (AMPs) that kill pathogenic bacteria such as H. pyloriand resistant E. coli under acidic environment with minimal impact to commensal bacteria whilst not causing antibiotic resistance.

EXPERIMENTS

Using a combined approach of cell assays, molecular dynamics (MD) simulations and membrane models facilitating biophysical and biochemical measurements including small angle neutron scattering (SANS), we have characterized the pH-responsive physiochemical properties and antimicrobial performance of two amphiphilic AMPs, GIIKDIIKDIIKDI-NH2 and GIIKKIIDDIIKKI-NH2 (denoted as 3D and 2D, respectively), that were designed by selective substitutions of cationic residues of Lys (K) in the extensively studied AMP G(IIKK)3I-NH2 with anionic residue Asp (D).

FINDINGS

Whilst 2D kept non-ordered coils across the entire pH range studied, 3D displayed a range of secondary structures when pH was shifted from basic to acidic, with distinct self-assembly into nanofibers in aqueous environment. Further experimental and modeling studies revealed that the AMPs interacted differently with the inner and outer membranes of Gram-negative bacteria in a pH-responsive manner and that the structural features characterized by membrane leakage and intramembrane nanoaggregates revealed from fluorescence spectroscopy and SANS were well linked to antimicrobial actions. Different antimicrobial efficacies of 2D and 3D were underlined by the interplay between their ability to bind to the outer membrane lipid LPS (lipopolysaccharide), outer membrane permeability change and inner membrane depolarization and leakage. Furthermore, AMP's binding with the inner membrane under acidic condition caused both the dissipation of membrane potential (Δψ) and the continuous dissipation of transmembrane ΔpH, with Δψ and ΔpH being the key components of the proton motive force. Combinations of antibiotic (Minocycline) with the pH-responsive AMP generated the synergistic effects against Gram-negative bacteria only under acidic condition. These features are crucial to target applications to gastric infections, anti-acne and wound healing.

Rational Design of a Potent Antimicrobial Peptide Based on the Active Region of a Gecko Cathelicidin

The emergence of multidrug-resistant (MDR) bacteria presents a significant challenge to public health, increasing the risk of infections that are resistant to current antibiotic treatment. Antimicrobial peptides (AMPs) offer a promising alternative to conventional antibiotics in the prevention of MDR bacterial infections. In the present study, we identified a novel cathelicidin AMP from Gekko japonicus, which exhibited broad-spectrum antibacterial activity against both Gram-negative and Gram-positive bacteria, with minimal inhibitory concentrations ranging from 2.34 to 4.69 μg/mL. To improve its potential therapeutic application, a series of peptides was synthesized based on the active region of the gecko-derived cathelicidin. The lead peptide (RH-16) showed an antimicrobial activity comparable to that of the parent peptide. Structural characterization revealed that RH-16 adopted an amphipathic α-helical conformation. Furthermore, RH-16 demonstrated neither hemolytic nor cytotoxic activity but effectively killed a wide range of clinically isolated, drug-resistant bacteria. The antimicrobial activity of RH-16 was attributed to the nonspecific targeting of bacterial membranes, leading to rapid bacterial membrane permeabilization and rupture. RH-16 also retained its antibacterial activity in plasma and exhibited mild toxicity in vivo. Notably, RH-16 offered robust protection against skin infection in a murine model. Therefore, this newly identified cathelicidin AMP may be a strong candidate for future pharmacological development targeting multidrug resistance. The use of a rational design approach for isolating the minimal antimicrobial unit may accelerate the transition of natural AMPs to clinically applicable antibacterial agents.

Antibacterial Activity and Mechanism of Polygonatum sibiricum Extract Against Bacillus cereus and Its Application in Pasteurized Milk

The purpose of this study was to reveal the antibacterial activity and mechanism of Polygonatum sibiricum extract (PSE) against Bacillus cereus and further analyze the application of PSE in pasteurized milk (PM). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values and growth curve analysis were used to evaluate the antibacterial activity of PSE against B. cereus. The changes in contents of intracellular adenosine 5'-triphosphate (ATP) and reactive oxygen species (ROS), activities of β-galactosidase, adenosine triphosphatase (ATPase) and alkaline phosphatase (AKP), cell membrane potential, protein and nucleic acid leakage, and cell morphology were used to reveal the antibacterial mechanism. The effects of PSE on viable count and sensory evaluation of PM during storage were analyzed. The results showed that the MIC and MBC values of PSE against B. cereus were 2 and 4 mg/mL, respectively. Growth curve analysis showed that PSE with a concentration of 2 MIC could completely inhibit the growth of B. cereus. After treatments with PSE, the levels of intracellular ATP and ROS, and activities of β-galactosidase, ATPase and AKP of B. cereus were significantly reduced (p < 0.05). Cell membrane was depolarized, amounts of protein and nucleic acid leakage were significantly increased (p < 0.05), and cell morphology was destroyed. Furthermore, PSE significantly reduced the viable count of B. cereus in PM and improved the sensory quality of PM during storage (p < 0.05). Together, our findings suggested that PSE had the desired effect as a natural preservative applied in PM.

E3MPH16: An efficient endosomolytic peptide for intracellular protein delivery

To facilitate the introduction of proteins, such as antibodies, into cells, a variety of delivery peptides have been engineered. These peptides are typically highly cationic and somewhat hydrophobic, enabling cytosolic protein delivery at the cost of causing cell damage by rupturing membranes. This balance between delivery effectiveness and cytotoxicity presents obstacles for their real-world use. To tackle this problem, we designed a new endosome-disruptive cytosolic delivery peptide, E3MPH16, inspired by mastoparan X (MP). E3MPH16 was engineered to incorporate three Glu (E3) and 16 His (H16) residues at the N- and C-termini of MP, respectively. The negative charges of E3 substantially mitigate the cell-surface damage induced by MP. The H16 segment is known to enhance cell-surface adsorption and endocytic uptake of the associated molecules. With these modifications, E3MPH16 was successfully trapped within endosomes. The acidification of endosomes is expected to protonate the side chains of E3 and H16, enabling E3MPH16 to rupture endosomal membranes. As a result, nearly 100% of cells achieved cytosolic delivery of a model biomacromolecule, Alexa Fluor 488-labeled dextran (10 kDa), via endosomal escape by co-incubation with E3MPH16. The delivery process also suggested the involvement of macropinocytosis and caveolae-mediated endocytosis. With the assistance of E3MPH16, Cre recombinase and anti-Ras-IgG delivered into HEK293 cells and HT1080 cells enabled gene recombination and inhibited cell proliferation, respectively. The potential for in vivo application of this intracellular delivery method was further validated by topically injecting the green fluorescent protein fused with a nuclear localization signal (NLS-GFP) along with E3MPH16 into Colon-26 tumor xenografts in mice.

Self-assembly of peptide nanomaterials at biointerfaces: molecular design and biomedical applications

Self-assembly is an important strategy for constructing ordered structures and complex functions in nature. Based on this, people can imitate nature and artificially construct functional materials with novel structures through the supermolecular self-assembly pathway of biological interfaces. Among the many assembly units, peptide molecular self-assembly has received widespread attention in recent years. In this review, we introduce the interactions (hydrophobic interaction, hydrogen bond, and electrostatic interaction) between peptide nanomaterials and biological interfaces, summarizing the latest advancements in multifunctional self-assembling peptide materials. We systematically demonstrate the assembly mechanisms of peptides at biological interfaces, such as proteins and cell membranes, while highlighting their application potential and challenges in fields like drug delivery, antibacterial strategies, and cancer therapy.

Fundamental Uses of Peptides as a New Model in Both Treatment and Diagnosis

An amino acid short chain is known as a peptide. Peptide bonds are the connections that hold the amino acids of a peptide together in a particular order. Characteristically, the shorter length of peptides helps to identify them from proteins. Different ways are used to classify peptides, including chain length, source of peptides, or their biological functions. The fact that peptides serve several purposes suggests that there is a foundation for improvement in peptide production and structure to enhance action. In addition, many patents on peptides for therapeutic and diagnostic approaches have been obtained. This review aims to give an overview of peptides used recently in treatment and diagnosis.

Designing peptide amphiphiles as novel antibacterials and antibiotic adjuvants against gram-negative bacteria

Gram-negative strains are intrinsically resistant to most antibiotics due to the robust and impermeable characteristic of their outer membrane. Self-assembling cationic peptide amphiphiles (PAs) have the ability to disrupt bacteria membranes, constituting an excellent antibacterial alternative to small molecule drugs that can be used alone or as antibiotic adjuvants to overcome bacteria resistance. PA1 (C16KHKHK), self-assembled into micelles, which exhibited low antibacterial activity against all strains tested, and showed strong synergistic antibacterial activity in combination with Vancomycin with a Fractional Inhibitory Concentration index (FICi) of 0.15 against E. coli. The molecules, PA2 (C16KRKR) and PA3 (C16AAAKRKR), also self-assembled into micelles, displayed a broad-spectrum antibacterial activity against all strains tested, and low susceptibility to resistance development over 21 days. Finally, PA1, PA 2 and PA3 displayed low cytotoxicity against mammalian cells, and PA2 showed a potent antibacterial activity and low toxicity in preliminary in vivo models using G. mellonella. The results show that PAs are a great platform for the future development of effective antibiotics to slow down the antibiotic resistance and can act as antibiotic adjuvants with synergistic mechanism of action, which can be repurposed for use with existing antibiotics commonly used to treat gram-positive bacteria to treat infections caused by gram-negative bacteria.

Antimicrobial peptide temporin derivatives inhibit biofilm formation and virulence factor expression of Streptococcus mutans

Introduction

Temporin-GHa obtained from the frog Hylarana guentheri showed bactericidal efficacy against Streptococcus mutans. To enhance its antibacterial activity, the derived peptides GHaR and GHa11R were designed, and their antibacterial performance, antibiofilm efficacy and potential in the inhibition of dental caries were evaluated.

Methods

Bacterial survival assay, fluorescent staining assay and transmission electron microscopy observation were applied to explore how the peptides inhibited and killed S. mutans. The antibiofilm efficacy was assayed by examining exopolysaccharide (EPS) and lactic acid production, bacterial adhesion and cell surface hydrophobicity. The gene expression level of virulence factors of S. mutans was detected by qRT-PCR. Finally, the impact of the peptides on the caries induced ability of S. mutans was measured using a rat caries model.

Results

It has been shown that the peptides inhibited biofilm rapid accumulation by weakening the initial adhesion of S. mutans and reducing the production of EPS. Meanwhile, they also decreased bacterial acidogenicity and aciduricity, and ultimately prevented caries development in vivo.

Conclusion

GHaR and GHa11R might be promising candidates for controlling S. mutans infections.

The membrane activity of the antimicrobial peptide caerin 1.1 is pH dependent

Antimicrobial peptides are an important class of membrane-active peptides that can provide alternatives or complements to classic antibiotics. Among the many classes of AMPs, the histidine-rich family is of particular interest since they may induce pH-sensitive interactions with cell membranes. The AMP caerin 1.1 (Cae-1), from Australian tree frogs, has three histidine residues, and thus we studied the pH dependence of its interactions with model cell membranes. Using NMR spectroscopy and molecular dynamics simulations, we showed that Cae-1 induced greater perturbation of the lipid dynamics and water penetrations within the membrane interior in an acidic environment compared with physiological conditions. Using 31P solid-state NMR, the packing, chemical environment, and dynamics of the lipid headgroup were monitored. 2H solid-state NMR showed that Cae-1 ordered the acyl chains of the hydrophobic core of the bilayer. These results supported the molecular dynamics data, which showed that Cae-1 was mainly inserted within the lipid bilayer for both neutral and negatively charged membranes, with the charged residues pulling the water and phosphate groups inward. This could be an early step in the mechanism of membrane disruption by histidine-rich antimicrobial peptides and indicated that Cae-1 acts via a transmembrane mechanism in bilayers of neutral and anionic phospholipid membranes, especially in acidic conditions.

Mechanochemical Preparation, Solid-State Characterization, and Antimicrobial Performance of Copper and Silver Nitrate Coordination Polymers with L- and DL-Arginine and Histidine

The antimicrobial activity of the novel coordination polymers obtained by co-crystallizing the amino acids arginine or histidine, as both enantiopure L and racemic DL forms, with the salts Cu(NO3)2 and AgNO3 has been investigated to explore the effect of chirality in the cases of enantiopure and racemic forms. The compounds [Cu·AA·(NO3)2]CPs and [Ag·AA·NO3]CPs (AA = L-Arg, DL-Arg, L-His, DL-His) were prepared by mechanochemical, slurry, and solution methods and characterized by X-ray single-crystal and powder diffraction in the cases of the copper coordination polymers, and by powder diffraction and by solid-state NMR spectroscopy in the cases of the silver compounds. The two pairs of coordination polymers, [Cu·L-Arg·(NO3)2·H2O]CP and [Cu·DL-Arg·(NO3)2·H2O]CP, and [Cu·L-Hys·(NO3)2·H2O]CP and [Cu·DL-His·(NO3)2·H2O]CP, have been shown to be isostructural in spite of the different chirality of the amino acid ligands. A similar structural analogy could be established for the silver complexes on the basis of SSNMR. The activity against the bacterial pathogens Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus was assessed by carrying out disk diffusion assays on lysogeny agar media showing that, while there is no significant effect arising from the use of enantiopure or chiral amino acids, the coordination polymers exert an appreciable antimicrobial activity comparable, when not superior, to that of the metal salts alone.

The biological role of charge distribution in linear antimicrobial peptides

INTRODUCTION

Antimicrobial peptides (AMP) have received particular attention due to their capacity to kill bacteria. Although much is known about them, peptides are currently being further researched. A large number of AMPs have been discovered, but only a few have been approved for topical use, due to their promiscuity and other challenges, which need to be overcome.

AREAS COVERED

AMPs are diverse in structure. Consequently, they have varied action mechanisms when targeting microorganisms or eukaryotic cells. Herein, the authors focus on linear peptides, particularly those that are alpha-helical structured, and examine how their charge distribution and hydrophobic amino acids could modulate their biological activity.

EXPERT OPINION

The world currently needs urgent solutions to the infective problems caused by resistant pathogens. In order to start the race for antimicrobial development from the charge distribution viewpoint, bioinformatic tools will be necessary. Currently, there is no software available that allows to discriminate charge distribution in AMPs and predicts the biological effects of this event. Furthermore, there is no software available that predicts the side-chain length of residues and its role in biological functions. More specialized software is necessary.

Unique insertion/deletion polymorphisms within histidine-rich region of histidine-rich glycoprotein in Thoroughbred horses

Histidine-rich glycoprotein (HRG) is abundant plasma protein with various effects on angiogenesis, coagulation, and immune responses. Previously, we identified the base and amino acid sequences of equine HRG (eHRG) and revealed that eHRG regulates neutrophil functions. In this study, we first conducted a large-scale gene analysis with DNA samples extracted from 1700 Thoroughbred horses and identified unique insertion/deletion polymorphisms in the histidine-rich region (HRR) of eHRG. Here we report two types of polymorphisms (deletion type 1 [D1] and deletion type 2 [D2]) containing either a 45 bp or 90 bp deletion in the HRR of eHRG, and five genotypes of eHRG (insertion/insertion [II], ID1, ID2, D1D1, and D1D2) in Thoroughbred horses. Allele frequency of I, D1, and D2, was 0.483, 0.480, and 0.037 and the incidence of each genotype was II: 23.4%, ID1: 46.2%, ID2: 3.6%, D1D1: 23.1%, and D1D2: 3.7%, respectively. The molecular weights of each plasma eHRG protein collected from horses with each genotype was detected as bands of different molecular size, which corresponded to the estimated amino acid sequence. The nickel-binding affinity of the D1 or D2 deletion eHRG was reduced, indicating a loss of function at the site. eHRG proteins show a variety of biological and immunological activities in vivo, and HRR is its active center, suggesting that genetic polymorphisms in eHRG may be involved in the performance in athletic ability, productivity, and susceptibility to infectious diseases in Thoroughbred horses.

Targeting cariogenic pathogens and promoting competitiveness of commensal bacteria with a novel pH-responsive antimicrobial peptide

Novel ecological antimicrobial approaches to dental caries focus on inhibiting cariogenic pathogens while enhancing the growth of health-associated commensal communities or suppressing cariogenic virulence without affecting the diversity of oral microbiota, which emphasize the crucial role of establishing a healthy microbiome in caries prevention. Considering that the acidified cariogenic microenvironment leads to the dysbiosis of microecology and demineralization of enamel, exploiting the acidic pH as a bioresponsive trigger to help materials and medications target cariogenic pathogens is a promising strategy to develop novel anticaries approaches. In this study, a pH-responsive antimicrobial peptide, LH12, was designed utilizing the pH-sensitivity of histidine, which showed higher cationicity and stronger interactions with bacterial cytomembranes at acidic pH. Streptococcus mutans was used as the in vitro caries model to evaluate the inhibitory effects of LH12 on the cariogenic properties, such as biofilm formation, biofilm morphology, acidurance, acidogenicity, and exopolysaccharides synthesis. The dual-species model of Streptococcus mutans and Streptococcus gordonii was established in vitro to evaluate the regulation effects of LH12 on the mixed species microbial community containing both cariogenic bacteria and commensal bacteria. LH12 suppressed the cariogenic properties and regulated the bacterial composition to a healthier condition through a dual-functional mechanism. Firstly, LH12-targeted cariogenic pathogens in response to the acidified microenvironment and suppressed the cariogenic virulence by inhibiting the expression of multiple virulence genes and two-component signal transduction systems. Additionally, LH12 elevated H₂O₂ production of the commensal bacteria and subsequently improved the ecological competitiveness of the commensals. The dual-functional mechanism made LH12 a potential bioresponsive approach to caries management.

Revealing the Changes in Saliva and Serum Proteins of Pigs with Meningitis Caused by Streptococcus Suis: A Proteomic Approach

Meningitis due to Streptococcus suis causes high mortality and morbidity on pig farms and has increasing zoonotic potential worldwide. Saliva proteome analysis would potentially be useful in elucidating pathophysiological changes and mining for new biomarkers to diagnose and monitor S. suis infection. The objective of this study was to investigate the changes in the salivary and serum proteome profile of piglets with meningitis. The LC-MS/MS TMT proteomic approach was used to analyze saliva and serum samples from 20 male piglets: 10 with meningitis and 10 healthy. In saliva, 11 proteins had higher and 10 had lower relative abundance in piglets with meningitis. The proteins with the highest relative abundance were metavinculin (VCL) and desmocollin-2 (DSC2). Adenosine deaminase (ADA) was selected for validation using a spectrophotometric assay and demonstrated excellent performance in the differentiation between healthy and pigs with meningitis due to S. suis. In serum, the most protruding changes occurred for one SERPIN and haptoglobin (HP). In saliva and serum, the highest number of proteins with altered abundance were linked, via the enrichment analysis, with platelet and neutrophil pathways. Overall, meningitis caused by S. suis resulted in specific proteome changes in saliva and serum, reflecting different pathophysiological mechanisms, and marking new potential biomarkers for this infection.

Host–Bacterial Interactions: Outcomes of Antimicrobial Peptide Applications

The bacterial membrane is part of a secretion system which plays an integral role to secrete proteins responsible for cell viability and pathogenicity; pathogenic bacteria, for example, secrete virulence factors and other membrane-associated proteins to invade the host cells through various types of secretion systems (Type I to Type IX). The bacterial membrane can also mediate microbial communities’ communication through quorum sensing (QS), by secreting auto-stimulants to coordinate gene expression. QS plays an important role in regulating various physiological processes, including bacterial biofilm formation while providing increased virulence, subsequently leading to antimicrobial resistance. Multi-drug resistant (MDR) bacteria have emerged as a threat to global health, and various strategies targeting QS and biofilm formation have been explored by researchers worldwide. Since the bacterial secretion systems play such a crucial role in host–bacterial interactions, this review intends to outline current understanding of bacterial membrane systems, which may provide new insights for designing approaches aimed at antimicrobials discovery. Various mechanisms pertaining interaction of the bacterial membrane with host cells and antimicrobial agents will be highlighted, as well as the evolution of bacterial membranes in evasion of antimicrobial agents. Finally, the use of antimicrobial peptides (AMPs) as a cellular device for bacterial secretion systems will be discussed as emerging potential candidates for the treatment of multidrug resistance infections.

Histidine-Mediated Ion Specific Effects Enable Salt Tolerance of a Pore-Forming Marine Antimicrobial Peptide

Antimicrobial peptides (AMPs) preferentially permeate prokaryotic membranes via electrostatic binding and membrane remodeling. Such action is drastically suppressed by high salt due to increased electrostatic screening, thus it is puzzling how marine AMPs can possibly work. We examine as a model system, piscidin-1, a histidine-rich marine AMP, and show that ion-histidine interactions play unanticipated roles in membrane remodeling at high salt: Histidines can simultaneously hydrogen-bond to a phosphate and coordinate with an alkali metal ion to neutralize phosphate charge, thereby facilitating multidentate bonds to lipid headgroups in order to generate saddle-splay curvature, a prerequisite to pore formation. A comparison among Na+ , K+ , and Cs+ indicates that histidine-mediated salt tolerance is ion specific. We conclude that histidine plays a unique role in enabling protein/peptide-membrane interactions that occur in marine or other high-salt environment.

Semenogelin, a coagulum macromolecule monitoring factor involved in the first step of fertilization: A prospective review

Human male infertility affects approximately 1/10 couples worldwide, and its prevalence is found more in developed countries. Along with sperm cells, the secretions of the prostate, seminal vesicle and epididymis plays a major role in proper fertilization. Many studies have proven the functions of seminal vesicle secretions, especially semenogelin protein, as an optimiser for fertilization. Semenogelin provides the structural components for coagulum formation after ejaculation. It binds with eppin and is found to have major functions like motility of sperm, transporting the sperm safely in the immune rich female reproductive tract until the sperm cells reach the egg intact. The capacitation process is essential for proper fertilization and semenogelin involved in mediating capacitation in time. Also, it has control of events towards the first step in the fertilization process. It is a Zn ions binding protein, and Zn ions act as a cofactor that helps in the proper motility of sperm cells. Therefore, any imbalance in protein that automatically affect sperm physiology and fertility status. This review sheds a comprehensive and critical view on the significant functions of semenogelin in fertilization. This review can open up advanced proteomics research on semenogelin towards unravelling molecular mechanisms in fertilization.

Exploring synergy and its role in antimicrobial peptide biology

Antimicrobial peptides will be an essential component in combating the escalating issue of antibiotic resistance. Identifying synergistic combinations of two or more substances will increase the value of these peptides further. Several potential pitfalls in conducting synergy testing with peptides are discussed in detail. As case studies, we describe observations of AMP synergy with peptides, antibiotics, and metal ions as well as some of the mechanistic details that have been uncovered. The Bliss and Loewe models for synergy are presented prior to recommending protocols for conducting checkerboard, minimal inhibitory concentration, and time-kill assays. Establishing mechanisms of action and exploring the potential for resistance will be crucial to translate these studies into the clinic.

Deuterium Solid State NMR Studies of Intact Bacteria Treated With Antimicrobial Peptides

Solid state NMR has been tremendously useful in characterizing the structure and dynamics of model membranes composed of simple lipid mixtures. Model lipid studies employing solid state NMR have included important work revealing how membrane bilayer structure and dynamics are affected by molecules such as antimicrobial peptides (AMPs). However, solid state NMR need not be applied only to model membranes, but can also be used with living, intact cells. NMR of whole cells holds promise for helping resolve some unsolved mysteries about how bacteria interact with AMPs. This mini-review will focus on recent studies using ²H NMR to study how treatment with AMPs affect membranes in intact bacteria.

[Role of histidine-rich glycoprotein as anti-DAMPs and therapeutic effects on DAMPs-related diseases]

Histidine-rich glycoprotein (HRG) is a plasma glycoprotein produced mainly in the liver. We have shown that HRG replacement therapy has a marked therapeutic effect on sepsis, in which high mobility group box 1 (HMGB1), one of the representative damage-associated molecular patterns (DAMPs), is known to play an important role in the disease progression. The mechanisms of action are diverse, including inhibition of immune thrombus formation and inhibition of ROS production. In addition, HRG has been shown to neutralize the toxicity of heme, a type of DAMPs, and neutralize the activity of LPS, a type of pathogen-associated molecular patterns (PAMPs), and to inhibit the translocation of HMGB1 from the nucleus of vascular endothelial cells to the extracellular space. Since DAMPs/PAMPs are known to play a central role in the pathogenesis of not only sepsis but also many inflammatory diseases, HRG has wide therapeutic applications and is considered to be a very promising seed for drug discovery.

A stepwise mutagenesis approach using histidine and acidic amino acid to engineer highly pH-dependent protein switches

Antibody-based drugs can be highly toxic, because they target normal tissue as well as tumor tissue. The pH value of the extracellular microenvironments around tumor tissues is lower than that of normal tissues. Therefore, antibodies that engage in pH-dependent binding at slightly acidic pH are crucial for improving the safety of antibody-based drugs. Thus, we implemented a stepwise mutagenesis approach to engineering pH-dependent antibodies capable of selective binding in the acidic microenvironment in this study. The first step involved single-residue histidine scanning mutagenesis of the antibody's complementarity-determining regions to prescreen for pH-dependent mutants and identify ionizable sensitive hot-spot residues that could be substituted by acidic amino acids to obtain pH-dependent antibodies. The second step involved single-acidic amino acid residue substitutions of the identified residues and the assessment of pH-dependent binding. We identified six ionizable sensitive hot-spot residues using single-histidine scanning mutagenesis. Nine pH-dependent antibodies were isolated using single-acidic amino acid residue mutagenesis at the six hot-spot residue positions. Relative to wild-type anti-CEA chimera antibody, the binding selectivity of the best performing mutant was improved by approximately 32-fold according to ELISA and by tenfold according to FACS assay. The mutant had a high affinity in the pH range of 5.5-6.0. This study supports the development of pH-dependent protein switches and increases our understanding of the role of ionizable residues in protein interfaces. The stepwise mutagenesis approach is rapid, general, and robust and is expected to produce pH-sensitive protein affinity reagents for various applications.

Biomaterial-Interrelated Bacterial Sweeper: Simplified Self-Assembled Octapeptides with Double-Layered Trp Zipper Induces Membrane Destabilization and Bacterial Apoptosis-Like Death

Treatment of microbial-associated infections continues to be hampered by impaired antibacterial efficiency and the variability in nanomedicines. Herein, an octapeptide library with a double-layered zipper, constructed via a systematic arrangement, simplifying the sequence and optimizing the structure (diverse motifs including surfactant-like, central-bola, and end-bola), is assessed in terms of biological efficiency and self-assembly properties. The results indicate that peptides with double-layered Trp zipper exhibit significant antimicrobial activity. Extracellularly, affinity interactions between micelles and bacteria induce the lateral flow of the membrane and electric potential perturbation. Intracellularly, lead molecules cause apoptosis-like death, as indicated by excessive accumulation of reactive oxygen species, generation of a DNA ladder, and upregulation of mazEF expression. Among them, RW-1 performs the best in vivo and in vitro. The intersecting combination of Trp zipper and surfactants possesses overwhelming superiority with respect to bacterial sweepers (therapeutic index [TI] = 52.89), nanostructures (micelles), and bacterial damage compared to RW-2 (central-bola) and RW-3 (end-bola). These findings confirm that the combination of double-layered Trp zipper and surfactants has potential for application as a combined motif for combating microbial infection and connects the vast gap between antimicrobial peptides and self-assembly, such as Jacob's ladder.

The Antimicrobial Peptide MK58911-NH2 Acts on Planktonic, Biofilm, and Intramacrophage Cells of Cryptococcus neoformans

Cryptococcosis is associated with high rates of morbidity and mortality, especially in AIDS patients. Its treatment is carried out by combining amphotericin B and azoles or flucytosine, which causes unavoidable toxicity issues in the host. Thus, the urgency in obtaining new antifungals drives the search for antimicrobial peptides (AMPs). This study aimed to extend the understanding of the mechanism of action of an AMP analog from wasp peptide toxins, MK58911-NH₂, on Cryptococcus neoformans. We also evaluated if MK58911-NH₂ can act on cryptococcal cells in macrophages, biofilms, and an immersion zebrafish model of infection. Finally, we investigated the structure-antifungal action and the toxicity relationship of MK58911-NH₂ fragments and a derivative of this peptide (MH58911-NH₂). The results demonstrated that MK58911-NH₂ did not alter the fluorescence intensity of the cell wall-binding dye calcofluor white or the capsule-binding dye 18b7 antibody-fluorescein isothiocyanate (FITC) in C. neoformans but rather reduced the number and size of fungal cells. This activity reduced the fungal burden of C. neoformans in both macrophages and zebrafish embryos as well as within biofilms. Three fragments of the MK58911-NH₂ peptide showed no activity against Cryptococcus and not toxicity in lung cells. The derivative peptide MH58911-NH₂, in which the lysine residues of MK58911-NH₂ were replaced by histidines, reduced the activity against extracellular and intracellular C. neoformans. On the other hand, it was active against biofilms and showed reduced toxicity. In summary, these results showed that peptide MK58911-NH₂ could be a promising agent against cryptococcosis. This work also opens a perspective for the verification of the antifungal activity of other derivatives.

The multifaceted nature of antimicrobial peptides: current synthetic chemistry approaches and future directions

Bacterial infections caused by 'superbugs' are increasing globally, and conventional antibiotics are becoming less effective against these bacteria, such that we risk entering a post-antibiotic era. In recent years, antimicrobial peptides (AMPs) have gained significant attention for their clinical potential as a new class of antibiotics to combat antimicrobial resistance. In this review, we discuss several facets of AMPs including their diversity, physicochemical properties, mechanisms of action, and effects of environmental factors on these features. This review outlines various chemical synthetic strategies that have been applied to develop novel AMPs, including chemical modifications of existing peptides, semi-synthesis, and computer-aided design. We will also highlight novel AMP structures, including hybrids, antimicrobial dendrimers and polypeptides, peptidomimetics, and AMP-drug conjugates and consider recent developments in their chemical synthesis.

Zn-Enhanced Asp-Rich Antimicrobial Peptides: N-Terminal Coordination by Zn(II) and Cu(II), Which Distinguishes Cu(II) Binding to Different Peptides

The antimicrobial activity of surfactant-associated anionic peptides (SAAPs), which are isolated from the ovine pulmonary surfactant and are selective against the ovine pathogen Mannheimia haemolytica, is strongly enhanced in the presence of Zn(II) ions. Both calorimetry and ITC measurements show that the unique Asp-only peptide SAAP3 (DDDDDDD) and its analogs SAAP2 (GDDDDDD) and SAAP6 (GADDDDD) have a similar micromolar affinity for Zn(II), which binds to the N-terminal amine and Asp carboxylates in a net entropically-driven process. All three peptides also bind Cu(II) with a net entropically-driven process but with higher affinity than they bind Zn(II) and coordination that involves the N-terminal amine and deprotonated amides as the pH increases. The parent SAAP3 binds Cu(II) with the highest affinity; however, as shown with potentiometry and absorption, CD and EPR spectroscopy, Asp residues in the first and/or second positions distinguish Cu(II) binding to SAAP3 and SAAP2 from their binding to SAAP6, decreasing the Cu(II) Lewis acidity and suppressing its square planar amide coordination by two pH units. We also show that these metal ions do not stabilize a membrane disrupting ability nor do they induce the antimicrobial activity of these peptides against a panel of human pathogens.

The Double-Edged Sword of Beta2-Microglobulin in Antibacterial Properties and Amyloid Fibril-Mediated Cytotoxicity

Beta2-microglobulin (B2M) a key component of major histocompatibility complex class I molecules, which aid cytotoxic T-lymphocyte (CTL) immune response. However, the majority of studies of B2M have focused only on amyloid fibrils in pathogenesis to the neglect of its role of antimicrobial activity. Indeed, B2M also plays an important role in innate defense and does not only function as an adjuvant for CTL response. A previous study discovered that human aggregated B2M binds the surface protein structure in Streptococci, and a similar study revealed that sB2M-9, derived from native B2M, functions as an antibacterial chemokine that binds Staphylococcus aureus. An investigation of sB2M-9 exhibiting an early lymphocyte recruitment in the human respiratory epithelium with bacterial challenge may uncover previously unrecognized aspects of B2M in the body’s innate defense against Mycobactrium tuberculosis. B2M possesses antimicrobial activity that operates primarily under pH-dependent acidic conditions at which B2M and fragmented B2M may become a nucleus seed that triggers self-aggregation into distinct states, such as oligomers and amyloid fibrils. Modified B2M can act as an antimicrobial peptide (AMP) against a wide range of microbes. Specifically, these AMPs disrupt microbe membranes, a feature similar to that of amyloid fibril mediated cytotoxicity toward eukaryotes. This study investigated two similar but nonidentical effects of B2M: the physiological role of B2M, in which it potentially acts against microbes in innate defense and the role of B2M in amyloid fibrils, in which it disrupts the membrane of pathological cells. Moreover, we explored the pH-governing antibacterial activity of B2M and acidic pH mediated B2M amyloid fibrils underlying such cytotoxicity.

Physicochemical Features and Peculiarities of Interaction of AMP with the Membrane

Antimicrobial peptides (AMPs) are anti-infectives that have the potential to be used as a novel and untapped class of biotherapeutics. Modes of action of antimicrobial peptides include interaction with the cell envelope (cell wall, outer- and inner-membrane). A comprehensive understanding of the peculiarities of interaction of antimicrobial peptides with the cell envelope is necessary to perform a rational design of new biotherapeutics, against which working out resistance is hard for microbes. In order to enable de novo design with low cost and high throughput, in silico predictive models have to be invoked. To develop an efficient predictive model, a comprehensive understanding of the sequence-to-function relationship is required. This knowledge will allow us to encode amino acid sequences expressively and to adequately choose the accurate AMP classifier. A shared protective layer of microbial cells is the inner, plasmatic membrane. The interaction of AMP with a biological membrane (native and/or artificial) has been comprehensively studied. We provide a review of mechanisms and results of interactions of AMP with the cell membrane, relying on the survey of physicochemical, aggregative, and structural features of AMPs. The potency and mechanism of AMP action are presented in terms of amino acid compositions and distributions of the polar and apolar residues along the chain, that is, in terms of the physicochemical features of peptides such as hydrophobicity, hydrophilicity, and amphiphilicity. The survey of current data highlights topics that should be taken into account to come up with a comprehensive explanation of the mechanisms of action of AMP and to uncover the physicochemical faces of peptides, essential to perform their function. Many different approaches have been used to classify AMPs, including machine learning. The survey of knowledge on sequences, structures, and modes of actions of AMP allows concluding that only possessing comprehensive information on physicochemical features of AMPs enables us to develop accurate classifiers and create effective methods of prediction. Consequently, this knowledge is necessary for the development of design tools for peptide-based antibiotics.

Advances of peptides for antibacterial applications

In the past few decades, peptide antibacterial products with unique antibacterial mechanisms have attracted widespread interest. They can effectively reduce the probability of drug resistance of bacteria and are biocompatible, so they possess tremendous development prospects. This review provides recent research and analysis on the basic types of antimicrobial peptides (including poly (amino acid)s, short AMPs, and lipopeptides) and factors to optimize antimicrobial effects. It also summarizes the two most important modes of action of antimicrobial peptides and the latest developments in the application of AMPs, including antimicrobial agent, wound healing, preservative, antibacterial coating and others. Finally, we discuss the remaining challenges to improve the antibacterial peptides and propose prospects in the field.

Action mode of cranberry anthocyanin on physiological and morphological properties of Staphylococcus aureus and its application in cooked meat

This study researched the action mode of cranberry anthocyanin (CA) against Staphylococcus aureus and the effect of CA on the counts of S. aureus and the quantity of cooked meat during storage. The antibacterial effect was assessed by minimum inhibitory concentration (MIC) and survival populations of S. aureus strains after CA treatments. The changes in intracellular adenosine 5'-triphosphate (ATP) concentration, cell membrane potential, content of bacterial protein and cell morphology were analyzed to reveal possible action mode. Application potentials of CA as antimicrobial agent were assessed during storage of cooked pork and beef. The result showed that the MIC of CA against S. aureus strains was 5 mg/mL. Approximately 8 log CFU/mL of S. aureus strains can be completely inhibited after treatment with 2.0 MIC of CA for 0.5 h. Treatments of CA resulted in lower intracellular ATP and soluble protein levels, damaged membrane structure and leakage of cytoplasmic. Application of CA on cooked pork and beef caused a significant decrease in S. aureus counts and pH values, and color-darkening compared with control samples. These findings demonstrated that CA played an effective antimicrobial against S. aureus and had a potential as natural preservative to inhibit the growth of food pathogens.

[Various functions of plasma histidine-rich glycoprotein and its clinical application as the biomarker and therapeutic drug for sepsis]

Histidine-rich glycoprotein (HRG) is a 75 kDa plasma glycoprotein synthesized in liver mainly, which exists at approximately 60-100 μg/ml in human plasma. HRG is known to bind to several ligands and cells, leading to exert coagulation, fibrinolysis, immune and inflammation regulatory activity in septic condition. Thus, decreased plasma HRG level induces the dysregulations of coagulation, fibrinolysis and immune system, resulting in disseminated intravascular coagulation and multiple organ failure. This article focuses on the physiological activity of HRG and the potential of HRG as the biomarker and therapeutic drug for sepsis.

Differential Susceptibility of Xylella fastidiosa Strains to Synthetic Bactericidal Peptides

The kinetics of cell inactivation and the susceptibility of Xylella fastidiosa subspecies fastidiosa, multiplex, and pauca to synthetic antimicrobial peptides from two libraries (CECMEL11 and CYCLO10) were studied. The bactericidal effect was dependent on the relative concentrations of peptide and bacterial cells, and was influenced by the diluent, either buffer or sap. The most bactericidal and lytic peptide was BP178, an enlarged derivative of the amphipathic cationic linear undecapeptide BP100. The maximum reduction in survivors after BP178 treatment occurred within the first 10 to 20 min of contact and at micromolar concentrations (<10 μM), resulting in pore formation in cell membranes, abundant production of outer membrane vesicles, and lysis. A threshold ratio of 10⁹ molecules of peptide per bacterial cell was estimated to be necessary to initiate cell inactivation. There was a differential susceptibility to BP178 among strains, with DD1 being the most resistant and CFBP 8173 the most susceptible. Moreover, strains showed a proportion of cells under the viable but nonculturable state, which was highly variable among strains. These findings may have implications for managing the diseases caused by X. fastidiosa.

A Placenta Derived C-Terminal Fragment of β-Hemoglobin With Combined Antibacterial and Antiviral Activity

The placenta acts as physical and immunological barrier against the transmission of viruses and bacteria from mother to fetus. However, the specific mechanisms by which the placenta protects the developing fetus from viral and bacterial pathogens are poorly understood. To identify placental peptides and small proteins protecting from viral and bacterial infections, we generated a peptide library from 10 kg placenta by chromatographic means. Screening the resulting 250 fractions against Herpes-Simplex-Virus 2 (HSV-2), which is rarely transmitted through the placenta, in a cell-based system identified two adjacent fractions with significant antiviral activity. Further rounds of chromatographic purification and anti-HSV-2 testing allowed to purify the bioactive peptide. Mass spectrometry revealed the presence of a 36-mer derived from the C-terminal region of the hemoglobin β subunit. The purified and corresponding chemically synthesized peptide, termed HBB(112–147), inhibited HSV-2 infection in a dose-dependent manner, with a mean IC₅₀ in the median μg/ml range. Full-length hemoglobin tetramer had no antiviral activity. HBB(112–147) did not impair infectivity by direct targeting of the virions but prevented HSV-2 infection at the cell entry level. The peptide was inactive against Human Immunodeficiency Virus Type 1, Rubella and Zika virus infection, suggesting a specific anti-HSV-2 mechanism. Notably, HBB(112–147) has previously been identified as broad-spectrum antibacterial agent. It is abundant in placenta, reaching concentrations between 280 and 740 μg/ml, that are well sufficient to inhibit HSV-2 and prototype Gram-positive and -negative bacteria. We here additionally show, that HBB(112–147) also acts potently against Pseudomonas aeruginosa strains (including a multi-drug resistant strain) in a dose dependent manner, while full-length hemoglobin is inactive. Interestingly, the antibacterial activity of HBB(112–147) was increased under acidic conditions, a hallmark of infection and inflammatory conditions. Indeed, we found that HBB(112–147) is released from the hemoglobin precursor by Cathepsin D and Napsin A, acidic proteases highly expressed in placental and other tissues. We propose that upon viral or bacterial infection, the abundant hemoglobin precursor is proteolytically processed to release HBB(112–147), a broadly active antimicrobial innate immune defense peptide.

Feedback Regulation of N Fixation in Frankia-Alnus Symbiosis Through Amino Acids Profiling in Field and Greenhouse Nodules

Symbiosis established between actinorhizal plants and Frankia spp., which are nitrogen-fixing actinobacteria, promotes nodule organogenesis, the site of metabolic exchange. The present study aimed to identify amino acid markers involved in Frankia-Alnus interactions by comparing nodules and associated roots from field and greenhouse samples. Our results revealed a high level of citrulline in all samples, followed by arginine (Arg), aspartate (Asp), glutamate (Glu), γ-amino-n-butyric acid (GABA), and alanine (Ala). Interestingly, the field metabolome approach highlighted more contrasted amino acid patterns between nodules and roots compared with greenhouse samples. Indeed, 12 amino acids had a mean relative abundance significantly different between field nodule and root samples, against only four amino acids in greenhouse samples, underlining the importance of developing "ecometabolome" approaches. In order to monitor the effects on Frankia cells (respiration and nitrogen fixation activities) of amino acid with an abundance pattern evocative of a role in symbiosis, in-vitro assays were performed by supplementing them in nitrogen-free cultures. Amino acids had three types of effects: i) those used by Frankia as nitrogen source (Glu, Gln, Asp), ii) amino acids stimulating both nitrogen fixation and respiration (e.g., Cit, GABA, Ala, valine, Asn), and iii) amino acids triggering a toxic effect (Arg, histidine). In this paper, a N-metabolic model was proposed to discuss how the host plant and bacteria modulate amino acids contents in nodules, leading to a fine regulation sustaining high bacterial nitrogen fixation.

Iron nano-complexes and iron chelate improve biological activities of sweet basil (Ocimum basilicum L.)

In this study, antioxidant and antimicrobial activities of basil (Ocimum basilicum L.) essential oil (EO) in response to different Fe sources (Fe-arginine, Fe-glycine, and Fe-histidine nano-complexes and Fe-EDDHA) were examined. EO samples were predominantly constituted by the phenylpropanoid methyl chavicol (53-89.5%). Application of Fe nano-complexes significantly increased the occurrence and concentration of sesquiterpenes, while decreased the content of oxygenated monoterpenes. Antioxidant activity of basil EOs was evaluated using free radical 2,2-diphenyl-1-picrylhydrazyl, Nitric oxide, H₂O₂ and Thiobarbituric acid reactive substances scavenging assays, and in all assays the highest and the lowest activities were recorded in basils supplied with Fe-histidine nano-complex (1.02, 1.62, 2.21, 3.22 mg mL-1) and control (3.89, 4.89, 5.52, 6.79 mg mL-1), respectively. Fe-histidine nano-complex was the most effective treatment to inhibit fungal (C. albicans: 0.058 mg mL-1; A. niger: 0.066 mg mL-1), Gram-negative (E. coli: 0.181 mg mL-1; S. typhimurium: 0.163 mg mL-1) and Gram-positive (B. subtilis: 0.033 mg mL-1; S. aureus: 0.002 mg mL-1) growth. In conclusion, application of iron nano-complexes significantly altered biological and pharmacological characteristics of basil EOs. Our results are quite encouraging since EOs exhibited potent antioxidant effect and antimicrobial activities.

An optimised Cu(0)-RDRP approach for the synthesis of lipidated oligomeric vinyl azlactone: toward a versatile antimicrobial materials screening platform

This report details the synthesis of lipidated 2-vinyl-4,4-dimethyl-5-oxazolone (VDM) oligomers via an optimised Cu(0)-mediated reversible-deactivation radical polymerisation approach, and the use of these oligomers as a versatile functional platform for the rapid generation of antimicrobial materials. The relative amounts of CuBr₂ and Me₆TREN were optimised to allow the fast and controlled polymerisation of VDM. These conditions were then used with the initiators ethyl 2-bromoisobutyrate, dodecyl 2-bromoisobutyrate, and (R)-3-((2-bromo-2-methylpropanoyl)oxy)propane-1,2-diyl didodecanoate to synthesise a library of oligo(VDM) (degree of polymerisation = 10) with ethyl, dodecyl or diglyceride end-groups. Subsequently, ring-opening of the pendant oxazolone group with various amines (i.e., 2-(2-aminoethyl)-1,3-di-Boc-guanidine, 1-(3-aminopropyl)imidazole, N-Boc-ethylenediamine, or N,N-dimethylethylenediamine) expanded the library to give 12 functional oligomers incorporating different cationic and lipid elements. The antimicrobial activities of these oligomers were assessed against a palette of bacteria and fungi: i.e. Staphylococcus aureus, Escherichia coli, Candida albicans, and Cryptococcus neoformans. The oligomers generally exhibited the greatest activity against the fungus, C. neoformans, with a minimum inhibitory concentration of 1 μg mL^-1 (comparable to the clinically approved antifungal fluconazole). To assess haemocompatibility, the oligomers were assayed against erythrocytes, with the primary amine or guanidine containing C₁₂ and 2C₁₂ oligomers exhibiting greater lysis against the red blood cells (HC₁₀ values between 7.1 and 43 μg mL^-1) than their imidazole and tertiary amine counterparts (HC₁₀ of >217 μg mL^-1). Oligomers showed the greatest selectivity for C. neoformans, with the C₁₂- and 2C₁₂-tertiary amine and C₁₂-imidazole oligomers possessing the greatest selectivity of >54-109. These results demonstrate the utility of reactive oligomers for rapidly assessing structure-property relationships for antibacterial and antifungal materials.

Discovery and Development of Novel Anti-fungal Peptides Against Foodspoiling Fungi

BACKGROUND

Despite the extensive research carried out to develop natural antifungal preservatives for food applications, there are very limited antifungal agents available to inhibit the growth of spoilage fungi in processed foods. Scope and Approach: Therefore, this review summarizes the discovery and development of antifungal peptides using lactic acid bacteria fermentation to prevent food spoilage by fungi. The focus of this review will be on the identification of antifungal peptides, potential sources, the possible modes of action and properties of peptides considered to inhibit the growth of spoilage fungi. Key Findings and Conclusions: Antifungal peptides generated by certain lactic acid bacteria strains have a high potential for applications in a broad range of foods. The mechanism of peptides antifungal activity is related to their properties such as low molecular weight, concentration and secondary structure. The antifungal peptides were proposed to be used as bio-preservatives to reduce and/or replace chemical preservatives.

Highly Stabilized α-Helical Coiled Coils Kill Gram-Negative Bacteria by Multicomplementary Mechanisms under Acidic Condition

Although antimicrobial peptides (AMPs) hold tremendous promise in overcoming the threats of multidrug resistance, the main obstacle to successful therapeutic applications is their poor stability. Various synthetic strategies such as unnatural amino acids and chemical modifications have made advances for improving this problem. However, this complicated synthesis often greatly increases the cost of production. Here, we show that a series of novel peptides, designed by combining an α-helical coiled coil model, knowledge of the specificity of proteolysis and major parameters of AMPs, exhibited efficient activity against all tested Gram-negative bacteria under acidic condition and demonstrate low toxicity. Of these α-helical coiled coil peptides, 3IH3 displayed the highest average therapeutic index (GM_TI = 294.25) with high stability toward salts, serum, extreme pH, heat, and proteases. Electron microscopy and biological analytical technique analyses showed that 3IH3 killed bacterial cells via a multicomplementary mechanism at pH 6.0, with physical membrane disruption as the dominant bactericidal mechanism. These results suggest that 3IH3 shows great stability as an inexpensive and effective antimicrobial activity agent and has the potential for clinical application in the treatment of infections occurring in body sites with acidic pH.