Antimicrobial activity of a 13 amino acid tryptophan-rich peptide derived from a putative porcine precursor protein of a novel family of antibacterial peptides

Harnessing antimicrobial peptides in endodontics

Endodontic therapy includes various procedures such as vital pulp therapy, root canal treatment and retreatment, surgical endodontic treatment and regenerative endodontic procedures. Disinfection and tissue repair are crucial for the success of these therapies, necessitating the development of therapeutics that can effectively target microbiota, eliminate biofilms, modulate inflammation and promote tissue repair. However, no current endodontic agents can achieve these goals. Antimicrobial peptides (AMPs), which are sequences of amino acids, have gained attention due to their unique advantages, including reduced susceptibility to drug resistance, broad-spectrum antibacterial properties and the ability to modulate the immune response of the organism effectively. This review systematically discusses the structure, mechanisms of action, novel designs and limitations of AMPs. Additionally, it highlights the efforts made by researchers to overcome peptide shortcomings and emphasizes the potential applications of AMPs in endodontic treatments.

Halogenated Antimicrobial Agents to Combat Drug-Resistant Pathogens

Antimicrobial resistance presents us with a potential global crisis as it undermines the abilities of conventional antibiotics to combat pathogenic microbes. The history of antimicrobial agents is replete with examples of scaffolds containing halogens. In this review, we discuss the impacts of halogen atoms in various antibiotic types and antimicrobial scaffolds and their modes of action, structure-activity relationships, and the contributions of halogen atoms in antimicrobial activity and drug resistance. Other halogenated molecules, including carbohydrates, peptides, lipids, and polymeric complexes, are also reviewed, and the effects of halogenated scaffolds on pharmacokinetics, pharmacodynamics, and factors affecting antimicrobial and antivirulence activities are presented. Furthermore, the potential of halogenation to circumvent antimicrobial resistance and rejuvenate impotent antibiotics is addressed. This review provides an overview of the significance of halogenation, the abilities of halogens to interact in biomolecular settings and enhance pharmacological properties, and their potential therapeutic usages in preventing a postantibiotic era. SIGNIFICANCE STATEMENT: Antimicrobial resistance and the increasing impotence of antibiotics are critical threats to global health. The roles and importance of halogen atoms in antimicrobial drug scaffolds have been established, but comparatively little is known of their pharmacological impacts on drug resistance and antivirulence activities. This review is the first to extensively evaluate the roles of halogen atoms in various antibiotic classes and pharmacological scaffolds and to provide an overview of their ability to overcome antimicrobial resistance.

Anticryptococcal activity and mechanistic studies of short amphipathic peptides

Cryptococcus neoformans, an opportunistic fungal pathogen, causes cryptococcosis in immunocompromised persons. A series of modified L-histidines-containing peptides are synthesized that exhibit promising activity against C. neoformans. Analog 11d [L-His(2-adamantyl)-L-Trp-L-His(2-phenyl)-OMe] produced potency with an IC₅₀ of 3.02 µg/ml (MIC = 5.49 µg/ml). This peptide is noncytotoxic and nonhaemolytic at the MIC and displays synergistic effects with amphotericin B at subinhibitory concentration. Mechanistic investigation of 11d using microscopic tools indicates cell wall and membrane disruption of C. neoformans, while flow cytometric analysis confirms cell death by apoptosis. This study indicates that 11d exhibits antifungal potential and acts via the rapid onset of action.

Specific Focus on Antifungal Peptides against Azole Resistant Aspergillus fumigatus: Current Status, Challenges, and Future Perspectives

The prevalence of fungal infections is increasing worldwide, especially that of aspergillosis, which previously only affected people with immunosuppression. Aspergillus fumigatus can cause allergic bronchopulmonary aspergillosis and endangers public health due to resistance to azole-type antimycotics such as fluconazole. Antifungal peptides are viable alternatives that combat infection by forming pores in membranes through electrostatic interactions with the phospholipids as well as cell death to peptides that inhibit protein synthesis and inhibit cell replication. Engineering antifungal peptides with nanotechnology can enhance the efficacy of these therapeutics at lower doses and reduce immune responses. This manuscript explains how antifungal peptides combat antifungal-resistant aspergillosis and also how rational peptide design with nanotechnology and artificial intelligence can engineer peptides to be a feasible antifungal alternative.

Activity and Synergy of Cu-ATCUN Antimicrobial Peptides

Antibiotic resistance demands innovative strategies and therapies. The pairs of antimicrobial peptides tested in this work show broad-spectrum synergy and are capable of interacting with diverse bacterial membranes. In most cases, the ATCUN motif enhanced the activity of peptides tested in combination. Our studies also show CP10A to be a multifaceted peptide, displaying both cell membrane and intracellular activity and acting as a chameleon, improving the activity of other peptides as needed. The results of the synergy experiments demonstrate the importance of varied modes of action and how these changes can affect the ability to combat pathogens, while also illustrating the value of the metal-binding domain in enhancing the activity of antimicrobial peptides in combination.

Hunting for Novel Routes in Anticancer Drug Discovery: Peptides against Sam-Sam Interactions

Among the diverse protein binding modules, Sam (Sterile alpha motif) domains attract attention due to their versatility. They are present in different organisms and play many functions in physiological and pathological processes by binding multiple partners. The EphA2 receptor contains a Sam domain at the C-terminus (EphA2-Sam) that is able to engage protein regulators of receptor stability (including the lipid phosphatase Ship2 and the adaptor Odin). Ship2 and Odin are recruited by EphA2-Sam through heterotypic Sam-Sam interactions. Ship2 decreases EphA2 endocytosis and consequent degradation, producing chiefly pro-oncogenic outcomes in a cellular milieu. Odin, through its Sam domains, contributes to receptor stability by possibly interfering with ubiquitination. As EphA2 is upregulated in many types of tumors, peptide inhibitors of Sam-Sam interactions by hindering receptor stability could function as anticancer therapeutics. This review describes EphA2-Sam and its interactome from a structural and functional perspective. The diverse design strategies that have thus far been employed to obtain peptides targeting EphA2-mediated Sam-Sam interactions are summarized as well. The generated peptides represent good initial lead compounds, but surely many efforts need to be devoted in the close future to improve interaction affinities towards Sam domains and consequently validate their anticancer properties.

Tryptophan, more than just an interfacial amino acid in the membrane activity of cationic cell-penetrating and antimicrobial peptides

Trp is unique among the amino acids since it is involved in many different types of noncovalent interactions such as electrostatic and hydrophobic ones, but also in π-π, π-cation, π-anion and π-ion pair interactions. In membranotropic peptides and proteins, Trp locates preferentially at the water-membrane interface. In antimicrobial or cell-penetrating peptides (AMPs and CPPs respectively), Trp is well-known for its strong role in the capacity of these peptides to interact and affect the membrane organisation of both bacteria and animal cells at the level of the lipid bilayer. This essential amino acid can however be involved in other types of interactions, not only with lipids, but also with other membrane partners, that are crucial to understand the functional roles of membranotropic peptides. This review is focused on this latter less known role of Trp and describes in details, both in qualitative and quantitative ways: (i) the physico-chemical properties of Trp; (ii) its effect in CPP internalisation; (iii) its importance in AMP activity; (iv) its role in the interaction of AMPs with glycoconjugates or lipids in bacteria membranes and the consequences on the activity of the peptides; (v) its role in the interaction of CPPs with negatively charged polysaccharides or lipids of animal membranes and the consequences on the activity of the peptides. We intend to bring highlights of the physico-chemical properties of Trp and describe its extensive possibilities of interactions, not only at the well-known level of the lipid bilayer, but with other less considered cell membrane components, such as carbohydrates and the extracellular matrix. The focus on these interactions will allow the reader to reevaluate reported studies. Altogether, our review gathers dedicated studies to show how unique are Trp properties, which should be taken into account to design future membranotropic peptides with expected antimicrobial or cell-penetrating activity.

Natural and Synthetic Halogenated Amino Acids-Structural and Bioactive Features in Antimicrobial Peptides and Peptidomimetics

The 3D structure and surface characteristics of proteins and peptides are crucial for interactions with receptors or ligands and can be modified to some extent to modulate their biological roles and pharmacological activities. The introduction of halogen atoms on the side-chains of amino acids is a powerful tool for effecting this type of tuning, influencing both the physico-chemical and structural properties of the modified polypeptides, helping to first dissect and then rationally modify features that affect their mode of action. This review provides examples of the influence of different types of halogenation in amino acids that replace native residues in proteins and peptides. Examples of synthetic strategies for obtaining halogenated amino acids are also provided, focusing on some representative compounds and their biological effects. The role of halogenation in native and designed antimicrobial peptides (AMPs) and their mimetics is then discussed. These are in the spotlight for the development of new antimicrobial drugs to counter the rise of antibiotic-resistant pathogens. AMPs represent an interesting model to study the role that natural halogenation has on their mode of action and also to understand how artificially halogenated residues can be used to rationally modify and optimize AMPs for pharmaceutical purposes.

Tandem Repeat of a Short Human Chemerin-Derived Peptide and Its Nontoxic d-Lysine-Containing Enantiomer Display Broad-Spectrum Antimicrobial and Antitubercular Activities

To design novel antimicrobial peptides by utilizing the sequence of the human host defense protein, chemerin, a seven-residue amphipathic stretch located in the amino acid region, 109-115, was identified, which possesses the highest density of hydrophobic and positively charged residues. Although this 7-mer peptide was inactive toward microorganisms, its 14-mer tandem repeat (Chem-KVL) was highly active against different bacteria including methicillin-resistant Staphylococcus aureus, a multidrug-resistant Staphylococcus aureus strain, and slow- and fast-growing mycobacterial species. The selective enantiomeric substitutions of its two l-lysine residues were attempted to confer cell selectivity and proteolytic stability to Chem-KVL. Chem-8dK with a d-lysine replacement in its middle (eighth position) showed the lowest hemolytic activity against human red blood cells among Chem-KVL analogues and maintained high antimicrobial properties. Chem-8dK showed in vivo efficacy against Pseudomonas aeruginosa infection in BALB/c mice and inhibited the development of resistance in this microorganism up to 30 serial passages and growth of intracellular mycobacteria in THP-1 cells.

Antimicrobial Peptides and Proteins: From Nature's Reservoir to the Laboratory and Beyond

Rapid rise of antimicrobial resistance against conventional antimicrobials, resurgence of multidrug resistant microbes and the slowdown in the development of new classes of antimicrobials, necessitates the urgent development of alternate classes of therapeutic molecules. Antimicrobial peptides (AMPs) are small proteins present in different lifeforms in nature that provide defense against microbial infections. They have been effective components of the host defense system for a very long time. The fact that the development of resistance by the microbes against the AMPs is relatively slower or delayed compared to that against the conventional antibiotics, makes them prospective alternative therapeutics of the future. Several thousands of AMPs have been isolated from various natural sources like microorganisms, plants, insects, crustaceans, animals, humans, etc. to date. However, only a few of them have been translated commercially to the market so far. This is because of some inherent drawbacks of the naturally obtained AMPs like 1) short half-life owing to the susceptibility to protease degradation, 2) inactivity at physiological salt concentrations, 3) cytotoxicity to host cells, 4) lack of appropriate strategies for sustained and targeted delivery of the AMPs. This has led to a surge of interest in the development of synthetic AMPs which would retain or improve the antimicrobial potency along with circumventing the disadvantages of the natural analogs. The development of synthetic AMPs is inspired by natural designs and sequences and strengthened by the fusion with various synthetic elements. Generation of the synthetic designs are based on various strategies like sequence truncation, mutation, cyclization and introduction of unnatural amino acids and synthons. In this review, we have described some of the AMPs isolated from the vast repertoire of natural sources, and subsequently described the various synthetic designs that have been developed based on the templates of natural AMPs or from de novo design to make commercially viable therapeutics of the future. This review entails the journey of the AMPs from their natural sources to the laboratory.

Modified histidine containing amphipathic ultrashort antifungal peptide, His[2-p-(n-butyl)phenyl]-Trp-Arg-OMe exhibits potent anticryptococcal activity

In pursuit of ultrashort peptide-based antifungals, a new structural class, His(2-aryl)-Trp-Arg is reported. Structural changes were investigated on His-Trp-Arg scaffold to demonstrate the impact of charge and lipophilic character on the biological activity. The presence and size of the aryl moiety on imidazole of histidine modulated overall amphiphilic character, and biological activity. Peptides exhibited IC₅₀ of 0.37-9.66 μg/mL against C. neoformans. Peptide 14f [His(2-p-(n-butyl)phenyl)-Trp-Arg-OMe] exhibited two-fold potency (IC₅₀ = 0.37 μg/mL, MIC = 0.63 μg/mL) related to amphotericin B, without any cytotoxic effects up to 10 μg/mL. Peptide 14f act by nuclear fragmentation, membranes permeabilization, disruption and pore formations in the microbial cells as determined by the mechanistic studies employing Trp-quenching, CLSM, SEM, and HR-TEM. The amalgamation of short sequence, presence of appropriate aryl group on l-histidine, potent anticryptococcal activity, no cytotoxicity, and detailed mechanistic studies directed to the identification of 14f as a new antifungal structural lead.

Beneficial Impacts of Incorporating the Non-Natural Amino Acid Azulenyl-Alanine into the Trp-Rich Antimicrobial Peptide buCATHL4B

Antimicrobial peptides (AMPs) present a promising scaffold for the development of potent antimicrobial agents. Substitution of tryptophan by non-natural amino acid Azulenyl-Alanine (AzAla) would allow studying the mechanism of action of AMPs by using unique properties of this amino acid, such as ability to be excited separately from tryptophan in a multi-Trp AMPs and environmental insensitivity. In this work, we investigate the effect of Trp→AzAla substitution in antimicrobial peptide buCATHL4B (contains three Trp side chains). We found that antimicrobial and bactericidal activity of the original peptide was preserved, while cytocompatibility with human cells and proteolytic stability was improved. We envision that AzAla will find applications as a tool for studies of the mechanism of action of AMPs. In addition, incorporation of this non-natural amino acid into AMP sequences could enhance their application properties.

A Thermostable, Modified Cathelicidin-Derived Peptide With Enhanced Membrane-Active Activity Against Salmonella enterica serovar Typhimurium

Foodborne illness caused by consumption of food contaminated with Salmonella is one of the most common causes of diarrheal disease and affects millions of people worldwide. The rising emergence and spread of antimicrobial resistance, especially in some serotypes of Salmonella, has raised a great awareness of public health issues worldwide. To ensure safety of the food processing chain, the development of new food preservatives must be expedited. Recently, thermal- and pH-stable antimicrobial peptides have received much attention for use in food production, and represent safe alternatives to chemical preservatives. A 12-mer cathelicidin-derived, α-helical cationic peptide, P7, displayed rapid killing activity, against strains of drug-resistant foodborne Salmonella enterica serovar Typhimurium and its monophasic variant (S. enterica serovar 4,5,12:i:-) and had minimal toxicity against mouse fibroblast cells. P7 tended to form helical structure in the membrane-mimic environments as evaluated by circular dichroism (CD) spectroscopy. The action mode of P7 at the membrane-level was affirmed by the results of flow cytometry, and confocal, scanning and transmission electron microscopy. P7 killed bacteria through binding to bacterial membranes, penetration and the subsequent accumulation in S. enterica serovar Typhimurium cytoplasm. This induced membrane depolarization, permeabilization, and sequential leakage of intracellular substances and cell death. Except for sensitivity to proteolytic digestive enzymes, P7 maintained its inhibitory activity against S. enterica serovar Typhimurium in the presence of different conditions [various salts, extreme pHs and heat (even at 100°C)]. Moreover, the peptide is unlikely to induce bacterial resistance in vitro. Taken together, this study demonstrated that the membrane-permeabilizing P7 peptide has much potential as a new antimicrobial agent for use in food processing and preservation.

Design of improved synthetic antifungal peptides with targeted variations in charge, hydrophobicity and chirality based on a correlation study between biological activity and primary structure of plant defensin γ-cores

Microbial resistance to available drugs is a growing health threat imposing the need for the development of new drugs. The scaffold of plant defensins, including their γ-cores, are particularly good candidates for drug design. This work aimed to improve the antifungal activity of a previous design peptide, named A₃₆,₄₂,₄₄γ_32-46VuDef (for short DD) against yeasts by altering its biochemical parameters. We explore the correlation of the biological activity and structure of plant defensins and compared their primary structures by superimposition with VuDef₁ and DD which indicated us the favorable position and the amino acid to be changed. Three new peptides with modifications in charge, hydrophobicity (RR and WR) and chirality (D-RR) were designed and tested against pathogenic yeasts. Inhibition was determined by absorbance. Viability of mammalian cells was determined by MTT. The three designed peptides had better inhibitory activity against the yeasts with better potency and spectrum of yeast species inhibition, with low toxicity to mammalian cells. WR, the most hydrophobic and cationic, exhibited better antifungal activity and lower toxicity. Our study provides experimental evidence that targeted changes in the primary structure of peptides based on plant defensins γ-core primary structures prove to be a good tool for the synthesis of new compounds that may be useful as alternative antifungal drugs. The method described did not have the drawback of synthesis of several peptides, because alterations are guided. When compared to other methods, the design process described is efficient and viable to those with scarce resources.

Investigation of the Role of Aromatic Residues in the Antimicrobial Peptide BuCATHL4B

BACKGROUND

Antimicrobial Peptides (AMPs) are an attractive alternative to traditional small molecule antibiotics as AMPs typically target the bacterial cell membrane. A Trp-rich peptide sequence derived from water buffalo (Bubalus bubalis), BuCATHL4B was previously identified as a broad-spectrum antimicrobial peptide.

OBJECTIVE

In this work, native Trp residues were replaced with other naturally occurring aromatic amino acids to begin to elucidate the importance of these residues on peptide activity.

METHODS

Minimal Inhibitory Concentration (MIC) results demonstrated activity against seven strains of bacteria. Membrane and bilayer permeabilization assays were performed to address the role of bilayer disruption in the activity of the peptides. Lipid vesicle binding and quenching experiments were also performed to gain an understanding of how the peptides interacted with lipid bilayers.

RESULTS

MIC results indicate the original, tryptophan-rich sequence, and the phenylalanine substituted sequences exhibit strong inhibition of bacterial growth. In permeabilization assays, peptides with phenylalanine substitutions have higher levels of membrane permeabilization than those substituted with tyrosine. In addition, one of the two-tyrosine substituted sequence, YWY, behaves most differently in the lowest antimicrobial activity, showing no permeabilization of bacterial membranes. Notably the antimicrobial activity is inherently species dependent, with varying levels of activity against different bacteria.

CONCLUSION

There appears to be little correlation between membrane permeabilization and activity, indicating these peptides may have additional mechanisms of action beyond membrane disruption. The results also identify two sequences, denoted FFF and YYW, which retain antibacterial activity but have markedly reduced hemolytic activity.

The Best Peptidomimetic Strategies to Undercover Antibacterial Peptides

Health-care systems that develop rapidly and efficiently may increase the lifespan of humans. Nevertheless, the older population is more fragile, and is at an increased risk of disease development. A concurrently growing number of surgeries and transplantations have caused antibiotics to be used much more frequently, and for much longer periods of time, which in turn increases microbial resistance. In 1945, Fleming warned against the abuse of antibiotics in his Nobel lecture: "The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant". After 70 years, we are witnessing the fulfilment of Fleming's prophecy, as more than 700,000 people die each year due to drug-resistant diseases. Naturally occurring antimicrobial peptides protect all living matter against bacteria, and now different peptidomimetic strategies to engineer innovative antibiotics are being developed to defend humans against bacterial infections.

Selective anticancer activity of synthetic peptides derived from the host defence peptide tritrpticin

Antimicrobial peptides (AMPs) constitute a diverse family of peptides with the ability to protect their host against microbial infections. In addition to their ability to kill microorganisms, several AMPs also exhibit selective cytotoxicity towards cancer cells and are collectively referred to as anticancer peptides (ACPs). Here a large library of AMPs, mainly derived from the porcine cathelicidin peptide, tritrpticin (VRRFPWWWPFLRR), were assessed for their anticancer activity against the Jurkat T cell leukemia line. These anticancer potencies were compared to the cytotoxicity of the peptides towards normal cells isolated from healthy donors, namely peripheral blood mononuclear cells (PBMCs) and red blood cells (RBCs; where hemolytic activity was assessed). Among the active tritrpticin derivatives, substitution of Arg by Lys enhanced the selectivity of the peptides towards Jurkat cells when compared to PBMCs. Additionally, the side chain length of the Lys residues was also optimized to further enhance the tritrpticin ACP selectivity at low concentrations. The mechanism of action of the peptides with high selectivity involved the permeabilization of the cytoplasmic membrane of Jurkat cells, without formation of apoptotic bodies. The incorporation of non-natural Lys-based cationic amino acids could provide a new strategy to improve the selectivity of other synthetic ACPs to enhance their potential for therapeutic use against leukemia cells.

The Ultrashort Peptide OW: A New Antibiotic Adjuvant

BACKGROUND

The over use of current antibiotics and low discovery rate of the new ones are leading to rapid development of multidrug-resistant pathogens worldwide. Antimicrobial peptides have shown promising results against multidrug-resistant bacteria.

OBJECTIVE

To investigate the antimicrobial activity of a new ultrashort hexapeptide (OW).

METHODS

The OW hexapeptide was designed and tested against different strains of bacteria with different levels of sensitivity. Bacterial susceptibility assays were performed according to the guidelines of the Clinical and Laboratory Institute (CLSI). The synergistic studies were then conducted using the Checkerboard assay. This was followed by checking the hemolytic effect of the hexapeptide against human blood cells and Human Embryonic Kidney cell line (HEK293). Finally, the antibiofilm activities of the hexapeptide were studied using the Biofilm Calgary method.

RESULTS

Synergistic assays showed that OW has synergistic effects with antibiotics of different mechanisms of action. It showed an outstanding synergism with Rifampicin against methicillin resistant Staphylococcus aureus; ΣFIC value was 0.37, and the MIC value of Rifampicin was decreased by 85%. OW peptide also displayed an excellent synergism with Ampicillin against multidrug-resistant Pseudomonas aeruginosa, with ΣFIC value of less than 0.38 and a reduction of more than 96% in the MIC value of Ampicillin.

CONCLUSION

This study introduced a new ultrashort peptide (OW) with promising antimicrobial potential in the management of drug-resistant infectious diseases as a single agent or in combination with commonly used antibiotics. Further studies are needed to investigate the exact mechanism of action of these peptides.

Short, symmetric-helical peptides have narrow-spectrum activity with low resistance potential and high selectivity

Broad-spectrum antibiotics have, until now, been the mainstay of antibiotic therapy. However, the increasing threat of drug-resistant bacteria and the ecological imbalance of normal microbial communities have forced a reconsideration of the best strategies to treat such pathogens. Therefore, antibacterial agents with specific abilities of eliminating pathogens may provide long-term protection. Antimicrobial peptides (AMPs), which can be optimized by modifying their primary sequences, are regarded as potentially valuable in development of pathogen-specific agents. To obtain efficient narrow-spectrum AMPs, database-filtering technology, which filters the most probable amino acid composition, positive charge, sequence length and hydrophobic content of peptides against Gram-negative bacteria, was taken as the first step. Then, the filtered parameters were distributed and modified into an α-helical symmetrical structure by considering the structure-function relationship of synthesized antimicrobial peptides. Finally, short, safe and stable peptides against Escherichia coli, Salmonella pullorum and Pseudomonas aeruginosa were successfully identified. The potential peptides F1 and F4 showed low cell toxicity, low resistance potential and low salt sensitivity. CD spectroscopy of the peptides illustrated that F1 and F4 exhibited a tendency towards an α-helical structure in a membrane-mimetic environment. Indeed, fluorescence spectroscopy and electron microscopy analyses indicated that the shorter potential sequence F4 killed the bacteria by causing physical destruction of the bacterial membrane and cytosol leakage. In the mouse model test, F4 reduced the bacterial load in major organs and the cytokine (TNF-α, IL-6, and IL-1β) levels in serum significantly (P < 0.05). Collectively, this symmetric-helical distribution, dependent on database-filtering parameters, is a promising strategy for designing effective smart AMPs with high cell selectivity, and it also provides new insights into the design and optimization of pathogen-specific biomaterials.

A comparison of activity, toxicity, and conformation of tritrpticin and two TOAC-labeled analogues. Effects on the mechanism of action

A strategy that has been gaining increased application for the study of the conformation, dynamics, orientation, and physicochemical properties of peptides is labeling with the paramagnetic amino acid TOAC. This approach was used to gain a deeper understanding on the mechanism of action of the antimicrobial peptide tritrpticin (TRP3). TRP3 was labeled with TOAC at the N-terminus (prior to V¹, TOAC⁰-TRP3) or internally (replacing P⁵, TOAC⁵-TRP3). Functional studies showed that labeling led to peptides with higher activity against Gram-positive bacteria and lower hemolytic activity with respect to TRP3. Peptide-induced model membranes permeabilization and ion channel-like activity studies corroborated the functional assays qualitatively, showing higher activity of the peptides against negatively charged membranes, which had the purpose of mimicking bacterial membranes. TOAC presented a greater freedom of motion at the N-terminus than at the internal position, as evinced by EPR spectra. EPR and fluorescence spectra reported on the peptides conformational properties, showing acquisition of a more packed conformation in the presence of the secondary structure-inducing solvent, TFE. CD studies showed that TOAC⁰-TRP3 acquires a conformation similar to that of TRP3, both in aqueous solution and in TFE, while TOAC⁵-TRP3 presents a different conformation in all environments. While the mechanism of action of TRP3 was impacted to some extent by TOAC labeling at the N-terminus, it did change upon replacement of P⁵ by TOAC. The results demonstrated that TOAC-labeling could be used to modulate TRP3 activity and mechanism of action and, more importantly, the critical role of P⁵ for TRP3 pore formation.

Novel Antibacterial Peptides Isolated from the Maillard Reaction Products of Half-Fin Anchovy (Setipinna taty) Hydrolysates/Glucose and Their Mode of Action in Escherichia coli

The Maillard reaction products (MRPs) of half-fin anchovy hydrolysates and glucose, named as HAHp(9.0)-G MRPs, were fractionated by size exclusion chromatography into three major fractions (F1⁻F3). F2, which demonstrated the strongest antibacterial activity against Escherichia coli (E. coli) and showed self-production of hydrogen peroxide (H₂O₂), was extracted by solid phase extraction. The hydrophobic extract of F2 was further isolated by reverse phase-high performance liquid chromatography into sub-fractions HE-F2-1 and HE-F2-2. Nine peptides were identified from HE-F2-1, and two peptides from HE-F2-2 using liquid chromatography-electrospray ionization/multi-stage mass spectrometry. Three peptides, FEDQLR (HGM-Hp1), ALERTF (HGM-Hp2), and RHPEYAVSVLLR (HGM-Hp3), with net charges of -1, 0, and +1, respectively, were synthesized. The minimal inhibitory concentration of these synthetic peptides was 2 mg/mL against E. coli. Once incubated with logarithmic growth phase of E. coli, HGM-Hp1 and HGM-Hp2 induced significant increases of both extracellular and intracellular H₂O₂ formation. However, HGM-Hp3 only dramatically enhanced intracellular H₂O₂ production in E. coli. The increased potassium ions in E. coli suspension after addition of HGM-Hp1 or HGM-Hp2 indicated the destruction of cell integrity via irreversible membrane damage. It is the first report of hydrolysates MRPs-derived peptides that might perform the antibacterial activity via inducing intracellular H₂O2 production.

Antibacterial effects of gold nanoparticles functionalized with the extracted peptide from Vespa orientalis wasp venom

The development of novel antimicrobial strategies is necessary because of the escalation of multidrug-resistant pathogens. Recently, antimicrobial peptides and their combination with nanoparticles were regarded as a promising tool to target drug-resistant pathogens. Herein, we evaluated antimicrobial efficacy of a peptide extracted from Vespa orientalis wasp venom and also its conjugation with gold nanoparticles. Nanoparticle conjugation measurement was done by evaluating the absorbance changes of the surface plasmon resonance band of gold nanoparticles at 555 nm. A significant increase in the antibacterial activity against gram negative and positive bacteria was obtained when the extracted peptide conjugated with gold nanoparticles. Finally, the results show that this new peptide-AuNps has the high practical potential for antibacterial activity and may provide an alternative therapy for bacterial infection.

Antimicrobial peptide delivery: an emerging therapeutic for the treatment of burn and wounds

The management of wounds and burns is becoming difficult using conventional therapeutics available due to resistance development by microbes. Therefore, there is an utmost need to develop therapeutic alternatives to these agents. Antimicrobial peptides have emerged as a novel class of agents for the effective management of wounds and burns due to their potent nature along with minimal chances of resistance development against them. This article focuses on highlighting the importance of these antimicrobial peptides among the various therapeutic alternatives for burns and wounds. Further, effective delivery strategies for these agents that are being employed and investigated are reported along with an overview of the importance of these agents in the coming years.

Sequential and Structural Aspects of Antifungal Peptides from Animals, Bacteria and Fungi Based on Bioinformatics Tools

Emerging drug resistance varieties and hyper-virulent strains of microorganisms have compelled the scientific fraternity to develop more potent and less harmful therapeutics. Antimicrobial peptides could be one of such therapeutics. This review is an attempt to explore antifungal peptides naturally produced by prokaryotes as well as eukaryotes. They are components of innate immune system providing first line of defence against microbial attacks, especially in eukaryotes. The present article concentrates on types, structures, sources and mode of action of gene-encoded antifungal peptides such as mammalian defensins, protegrins, tritrpticins, histatins, lactoferricins, antifungal peptides derived from birds, amphibians, insects, fungi, bacteria and their synthetic analogues such as pexiganan, omiganan, echinocandins and Novexatin. In silico drug designing, a major revolution in the area of therapeutics, facilitates drug development by exploiting different bioinformatics tools. With this view, bioinformatics tools were used to visualize the structural details of antifungal peptides and to predict their level of similarity. Current practices and recent developments in this area have also been discussed briefly.

Tryptophan-Rich and Proline-Rich Antimicrobial Peptides

Due to the increasing emergence of drug-resistant pathogenic microorganisms, there is a world-wide quest to develop new-generation antibiotics. Antimicrobial peptides (AMPs) are small peptides with a broad spectrum of antibiotic activities against bacteria, fungi, protozoa, viruses and sometimes exhibit cytotoxic activity toward cancer cells. As a part of the native host defense system, most AMPs target the membrane integrity of the microorganism, leading to cell death by lysis. These membrane lytic effects are often toxic to mammalian cells and restrict their systemic application. However, AMPs containing predominantly either tryptophan or proline can kill microorganisms by targeting intracellular pathways and are therefore a promising source of next-generation antibiotics. A minimum length of six amino acids is required for high antimicrobial activity in tryptophan-rich AMPs and the position of these residues also affects their antimicrobial activity. The aromatic side chain of tryptophan is able to rapidly form hydrogen bonds with membrane bilayer components. Proline-rich AMPs interact with the 70S ribosome and disrupt protein synthesis. In addition, they can also target the heat shock protein in target pathogens, and consequently lead to protein misfolding. In this review, we will focus on describing the structures, sources, and mechanisms of action of the aforementioned AMPs.

Natural Antimicrobial Peptides as Inspiration for Design of a New Generation Antifungal Compounds

Invasive fungal infections are associated with high mortality rates, despite appropriate antifungal therapy. Limited therapeutic options, resistance development and the high mortality of invasive fungal infections brought about more concern triggering the search for new compounds capable of interfering with fungal viability and virulence. In this context, peptides gained attention as promising candidates for the antimycotics development. Variety of structural and functional characteristics identified for various natural antifungal peptides makes them excellent starting points for design novel drug candidates. Current review provides a brief overview of natural and synthetic antifungal peptides.

Recombinant expression, antimicrobial activity and mechanism of action of tritrpticin analogs containing fluoro-tryptophan residues

The increase in antibiotic-resistant bacterial infections has prompted significant academic research into new therapeutic agents targeted against these pathogens. Antimicrobial peptides (AMPs) appear as promising candidates, due their potent antimicrobial activity and their ubiquitous presence in almost all organisms. Tritrpticin is a member of this family of peptides and has been shown to exert a strong antimicrobial activity against several bacterial strains. Tritrpticin's main structural characteristic is the presence of three consecutive Trp residues at the center of the peptide. These residues play an important role in the activity of tritrpticin against Escherichia coli. In this work, a recombinant version of tritrpticin was produced in E. coli using calmodulin as a fusion protein expression tag to overcome the toxicity of the peptide. When used in combination with glyphosate, an inhibitor of the endogenous synthesis of aromatic amino acids, this expression system allowed for the incorporation of fluorinated Trp analogs at very high levels (>90%). The antimicrobial activity of the 4-, 5- and 6-fluoro-Trp-containing tritrpticins against E. coli was as strong as the activity of the native peptide. Similarly, the tritrpticin analogs exhibited comparable abilities to perturb and permeabilize synthetic lipid bilayers as well as the outer and inner membrane of E. coli. Furthermore, the use of 19F NMR spectroscopy established that each individual fluoro-Trp residue interacts differently with SDS micelles, supporting the idea that each Trp in the original tritrpticin plays a different role in the perturbing/permeabilizing activity of the peptide. Moreover, our work demonstrates that the use of fluoro-Trp in solvent perturbation 19F NMR experiments provides detailed site-specific information on the insertion of the Trp residues in biological membrane mimetics. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Inhibition of phospho-MurNAc-pentapeptide translocase (MraY) by nucleoside natural product antibiotics, bacteriophage ϕX174 lysis protein E, and cationic antibacterial peptides

This review covers recent developments in the inhibition of translocase MraY and related phospho-GlcNAc transferases WecA and TagO, and insight into the inhibition and catalytic mechanism of this class of integral membrane proteins from the structure of Aquifex aeolicus MraY. Recent studies have also identified a protein-protein interaction site in Escherichia coli MraY, that is targeted by bacteriophage ϕX174 lysis protein E, and also by cationic antimicrobial peptides containing Arg-Trp close to their N- or C-termini.

Cyclic Tritrpticin Analogs with Distinct Biological Activities

Tritrpticin is a Trp-, Arg-, and Pro-rich cathelicidin peptide with promising antimicrobial activity. Cyclic analogs of tritrpticin were designed using two different approaches: circularization of the backbone by a head-to-tail peptide bond (TritrpCyc) or disulfide bridging between two Cys residues introduced at the termini of the peptide (TritrpDisu). Compared to the parent peptide, TritrpCyc has greatly improved therapeutic potential, showing stronger bactericidal activities and diminished hemolytic activity. Unexpectedly, the opposite effect was observed for TritrpDisu, which has lost its antimicrobial activity and is very hemolytic. In a membrane mimetic environment, NMR spectra show that TritrpDisu adopts an amphipathic turn-turn structure similar to linear tritrpticin. The structure of membrane-bound TritrpCyc has some similarity to that of TritrpDisu; however, the lipid interactions were not sufficient to restrain the structure of the former peptide in a single well-defined conformation. To help explain the distinct biological properties of the analogs, experiments investigating alternative antimicrobial targets were pursued: the membrane bilayer, lipopolysaccharides, and DNA. Although the hemolytic activity of TritrpDisu can be explained by the peptide's ability to induce higher leakage from the model mammalian membranes, TritrpCyc and TritrpDisu show no significant differences in these functional assays. Overall, our studies show that TritrpCyc holds great promise as a candidate for further development toward antimicrobial therapy.

Archetypal tryptophan-rich antimicrobial peptides: properties and applications

Drug-resistant microorganisms ('superbugs') present a serious challenge to the success of antimicrobial treatments. Subsequently, there is a crucial need for novel bio-control agents. Many antimicrobial peptides (AMPs) show a broad-spectrum activity against bacteria, fungi or viruses and are strong candidates to complement or substitute current antimicrobial agents. Some AMPs are also effective against protozoa or cancer cells. The tryptophan (Trp)-rich peptides (TRPs) are a subset of AMPs that display potent antimicrobial activity, credited to the unique biochemical properties of tryptophan that allow it to insert into biological membranes. Further, many Trp-rich AMPs cross bacterial membranes without compromising their integrity and act intracellularly, suggesting interactions with nucleic acids and enzymes. In this work, we overview some archetypal TRPs derived from natural sources, i.e., indolicidin, tritrpticin and lactoferricin, summarising their biochemical properties, structures, antimicrobial activities, mechanistic studies and potential applications.

Design and studies of multiple mechanism of anti-Candida activity of a new potent Trp-rich peptide dendrimers

PURPOSE

Eight peptide dendrimers were designed as structural mimics of natural cationic amphiphilic peptides with antifungal activity and evaluated for their anti-Candida potential against the wild type strains and mutants.

METHODS

Dendrimer 14 containing four Trp residues and dodecyl tail and a slightly smaller dendrimer 9 decorated with four N-methylated Trp that displayed 100 and 99.7% of growth inhibition at 16 μg/mL respectively, were selected for evaluation against the Candida albicans mutants with disabled biosynthesis of aspartic proteases responsible for host tissue colonization and morphogenesis during biofilm formation (sessile model). Flow cytometry method was employed to detect apoptotic cells with membrane alterations (phosphatidylserine translocation), and differentiation of apoptotic from necrotic cells was also performed. Simultaneous staining of cell surface phosphatidylserine with Annexin-V-Fluorescein and necrotic cells with propidium iodide was conducted.

RESULTS

14 at 16 μg/mL caused C. albicans cells to undergo cellular apoptosis but its increasing concentrations induced necrosis. 14 influenced C. albicans biofilm viability as well as hyphal and cell wall morphology. Confocal microscopy and cell wall staining with calcofluor white revealed that in epithelial model the cell surface structure was perturbed at MIC of peptide dendrimer. It appears that tryptophan or 1-methyltryptophan groups displayed at the surface and positive charges hidden in the dendrimer tree along with hydrocarbon tail located at C-terminus are important for the anti-Candida activity since dendrimers containing tryptamine at C-terminus showed only a moderate activity.

CONCLUSIONS

Our results suggest that membranolytic dendrimer 14, targeting cellular apoptotic pathway and impairing the cell wall formation in mature biofilm, may be a potential multifunctional antifungal lead compound for the control of C. albicans infections.

Synthesis, evaluation and molecular docking studies of amino acid derived N-glycoconjugates as antibacterial agents

Six amino acid derived N-glycoconjugates of d-glucose were synthesized, characterized and tested for antibacterial activity against G(+)ve (Bacillus cereus) as well as G(-)ve (Escherichia coli and Klebsiella pneumoniae) bacterial strains. All the tested compounds exhibited moderate to good antibacterial activity against these bacterial strains. The results were compared with the antibacterial activity of standard drug Chloramphenicol, where results of A5 (Tryptophan derived glycoconjugates) against E. coli and A4 (Isoleucine derived glycoconjugates) against K. pneumoniae bacterial strains are comparable with the standard drug molecule. In silico docking studies were also performed in order to understand the mode of action and binding interactions of these molecules. The docking studies revealed that, occupation of compound A5 at the ATP binding site of subunit GyrB (DNA gyrase, PDB ID: 3TTZ) via hydrophobic and hydrogen bonding interactions may be the reason for its significant in vitro antibacterial activity.

Effect of recombinant prophenin 2 on the integrity and viability of Trichomonas vaginalis

Trichomonas vaginalis is the causal agent of trichomoniasis, which is associated with preterm child delivery, low birth weight, and an increased risk of infection by human papilloma virus and human immunodeficiency virus following exposure. Several reports have established increasing numbers of trichomoniasis cases resistant to metronidazole, the agent used for treatment, and it is therefore important to identify new therapeutic alternatives. Previously, our group reported the effect of tritrpticin, a synthetic peptide derived from porcine prophenin, on T. vaginalis; however, the hemolytic activity of this small peptide complicates its possible use as a therapeutic agent. In this study, we report that the propeptide and the processed peptide of prophenin 2 (cleaved with hydroxylamine) affected the integrity and growth of T. vaginalis and that pro-prophenin 2 displays some resistance to proteolysis by T. vaginalis proteinases at 1 h. Its effect on T. vaginalis as well as its low hemolytic activity and short-time stability to parasite proteinases makes prophenin 2 an interesting candidate for synergistic or alternative treatment against T. vaginalis.

Investigation of the antimicrobial activity and biocompatibility of magnesium alloy coated with HA and antimicrobial peptide

Implant-associated infection is one of the biggest problems in orthopedic surgery. Antimicrobial peptides (AMPs) are well-known components of the innate immunity and less susceptible to the development of pathogen resistance compared to conventional antibiotics. Magnesium alloys as potential biodegradable bone implants have been received much attention in biomaterials field. This study investigated the deposition of calcium phosphate (CaP) coatings and loading of AMPs on the magnesium alloy surface by a biomimetic method. Scanning electron microscope (SEM) results presented that a microporous and plate-like CaP coating was processed on the magnesium alloy surface. X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis showed the main component of coating was hydroxyapatite (HA). Degradation assay in vitro showed that the HA coating deposited onto the magnesium alloy was corroded more slowly than the bare one. The amount of AMP loaded in the HA coating was 11.16±1.99 μg/cm2. The AMP loaded onto HA coatings had slow release for 7 days. The AMP-loaded coating showed antimicrobial activity against Staphylococcus aureus. Its bacterial inhibition rate exceeded 50% after 4 days and the antibacterial effect was sustained for 7 days. The coated magnesium alloys loaded with AMP could improve rat bone marrow mesenchymal stem cells (rBMMSCs) proliferation. Furthermore, it could also promote alkaline phosphatase (ALP) activity of rBMMSCs. Both radiographic evaluation and histopathology analysis demonstrated that implantation of the coated magnesium alloy into the rabbit femoral condyle had promoted bone repair and showed anti-inflammatory effect. The results showed that the AMP loaded onto HA coatings on the magnesium alloy surface could be considered an ideal orthopedic implant against S. aureus infection.

Antimicrobial peptides: a new class of antimalarial drugs?

A range of antimicrobial peptides (AMP) exhibit activity on malaria parasites, Plasmodium spp., in their blood or mosquito stages, or both. These peptides include a diverse array of both natural and synthetic molecules varying greatly in size, charge, hydrophobicity, and secondary structure features. Along with an overview of relevant literature reports regarding AMP that display antiplasmodial activity, this review makes a few considerations about those molecules as a potential new class of antimalarial drugs.

Position-Dependent Influence of the Three Trp Residues on the Membrane Activity of the Antimicrobial Peptide, Tritrpticin

Antimicrobial peptides (AMPs) constitute promising candidates for the development of new antibiotics. Among the ever-expanding family of AMPs, tritrpticin has strong antimicrobial activity against a broad range of pathogens. This 13-residue peptide has an unusual amino acid sequence that is almost symmetrical and features three central Trp residues with two Arg residues near each end of the peptide. In this work, the role of the three sequential Trp residues in tritrpticin was studied in a systematic fashion by making a series of synthetic peptides with single-, double- and triple-Trp substitutions to Tyr or Ala. ¹H NMR and fluorescence spectroscopy demonstrated the ability of all of the tritrpticin-analog peptides to interact with negatively-charged membranes. Consequently, most tritrpticin analogs exhibited the ability to permeabilize synthetic ePC:ePG (egg-yolk phosphatidylcholine (ePC), egg-yolk phosphatidylglycerol (ePG)) vesicles and live Escherichia coli bacteria. The membrane perturbation characteristics were highly dependent on the location of the Trp residue substitution, with Trp6 being the most important residue and Trp8 the least. The membrane permeabilization activity of the peptides in synthetic and biological membranes was directly correlated with the antimicrobial potency of the peptides against E. coli. These results contribute to the understanding of the role of each of the three Trp residues to the antimicrobial activity of tritrpticin.

Molecular understanding of a potential functional link between antimicrobial and amyloid peptides

Antimicrobial and amyloid peptides do not share common sequences, typical secondary structures, or normal biological activity but both the classes of peptides exhibit membrane-disruption ability to induce cell toxicity. Different membrane-disruption mechanisms have been proposed for antimicrobial and amyloid peptides, individually, some of which are not exclusive to either peptide type, implying that certain common principles may govern the folding and functions of different cytolytic peptides and associated membrane disruption mechanisms. Particularly, some antimicrobial and amyloid peptides have been identified to have dual complementary amyloid and antimicrobial properties, suggesting a potential functional link between amyloid and antimicrobial peptides. Given that some similar structural and membrane-disruption characteristics exist between the two classes of peptides, this review summarizes major findings, recent advances, and future challenges related to antimicrobial and amyloid peptides and strives to illustrate the similarities, differences, and relationships in the sequences, structures, and membrane interaction modes between amyloid and antimicrobial peptides, with a special focus on direct interactions of the peptides with the membranes. We hope that this review will stimulate further research at the interface of antimicrobial and amyloid peptides - which has been studied less intensively than either type of peptides - to decipher a possible link between both amyloid pathology and antimicrobial activity, which can guide drug design and peptide engineering to influence peptide-membrane interactions important in human health and diseases.

Antimicrobial Effects of a Hexapetide KCM21 against Pseudomonas syringae pv. tomato DC3000 and Clavibacter michiganensis subsp. michiganensis

Antimicrobial peptides (AMPs) are small but effective cationic peptides with variable length. In previous study, four hexapeptides were identified that showed antimicrobial activities against various phytopathogenic bacteria. KCM21, the most effective antimicrobial peptide, was selected for further analysis to understand its modes of action by monitoring inhibitory effects of various cations, time-dependent antimicrobial kinetics, and observing cell disruption by electron microscopy. The effects of KCM21 on Gram-negative strain, Pseudomonas syringae pv. tomato DC3000 and Gram-positive strain, Clavibacter michiganensis subsp. michiganensis were compared. Treatment with divalent cations such as Ca(2+) and Mg(2+) inhibited the bactericidal activities of KCM21 significantly against P. syringae pv. tomato DC3000. The bactericidal kinetic study showed that KCM21 killed both bacteria rapidly and the process was faster against C. michiganensis subsp. michiganensis. The electron microscopic analysis revealed that KCM21 induced the formation of micelles and blebs on the surface of P. syringae pv. tomato DC3000 cells, while it caused cell rupture against C. michiganensis subsp. michiganensis cells. The outer membrane alteration and higher sensitivity to Ca(2+) suggest that KCM21 interact with the outer membrane of P. syringae pv. tomato DC3000 cells during the process of killing, but not with C. michiganensis subsp. michiganensis cells that lack outer membrane. Considering that both strains had similar sensitivity to KCM21 in LB medium, outer membrane could not be the main target of KCM21, instead common compartments such as cytoplasmic membrane or internal macromolecules might be a possible target(s) of KCM21.

Hydroxy-tryptophan containing derivatives of tritrpticin: modification of antimicrobial activity and membrane interactions

Tritrpticin is an antimicrobial peptide with a strong microbicidal activity against Gram-positive and Gram-negative bacteria as well as fungi. The 13-residue peptide is essentially symmetrical and possesses a unique cluster of three Trp residues near the center of its amino acid sequence. The mechanism of action of tritrpticin is believed to involve permeabilization of the cytoplasmic membrane of susceptible bacteria. However it has been suggested that intracellular targets may also play a role in its antimicrobial activity. In this work the mechanism of action of several tritrpticin derivatives was studied through substitution of the three Trp residues with 5-hydroxy-tryptophan (5OHW), a naturally occurring non-ribosomal amino acid. Although it is more polar, 5OHW preserves many of the biophysical and biochemical properties of Trp, allowing the use of fluorescence spectroscopy and NMR techniques to study the interaction of the modified peptides with membrane mimetics. Single or triple 5OHW substitution did not have a large effect on the MIC of the parent peptide against Escherichia coli and Bacillus subtilis. However, the mechanism of action was altered by simultaneously replacing all three Trp with 5OHW. Our results suggest that the inner membrane of Gram-negative bacteria did not constitute the main target of this particular tritrpticin derivative. Since the addition of a hydroxyl group to the indole motif of the Trp residue was able to modify the mechanism of action of the peptides, our data confirm the importance of the Trp cluster in tritrpticin. This work also shows that 5OHW constitutes a new probe to modulate the antimicrobial activity and mechanism of action of other Trp-rich antimicrobial peptides.

Cecropin A-melittin mutant with improved proteolytic stability and enhanced antimicrobial activity against bacteria and fungi associated with gastroenteritis in vitro

Cecropin A-melittin (CAM), a chimeric antimicrobial peptide with potent antimicrobial activity, is threatened by some special extracellular proteases when used to deal with certain drug-resistant pathogenic microbes in the gastrointestinal tract. Thus, a four-tryptophan-substitution mutant (CAM-W) from CAM was developed via the replacement of special amino acid residues to enhance the antimicrobial potency and to improve the proteolytic stability of this agent. The pharmaceutical index of CAM-W was investigated, with a focus on biological potency, cytotoxicity, and proteolytic stability, as well as pH and thermal resistance. CAM-W exhibited potent antimicrobial activity and was approximately 3-12 times higher than that of CAM. CAM-W also exhibited a strong antifungal activity against a series of common pathogenic fungi, in a lower IC50 range between 2.1mg/L and 3.3mg/L than that of its reference CAM ranging from 9.8mg/L to 14.2mg/L. Besides, CAM-W showed moderate cytotoxicity (IC50>300mg/L) in erythrocyte lysis test. In addition, CAM-W overcame challenges under various conditions, including specific temperatures (20, 30, 40, 50, 60, 70, 80, and 90°C), pH values (2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0), and proteases (trypsin, pepsin, human neutrophil elastase, Pseudomonas aeruginosa elastase, and Staphylococcus aureus V8 protease) that are commonly present in human gastrointestinal tract. These results suggest that the four-tryptophan-substitution can confer CAM-W with a high pharmaceutical index, which is important for CAM-W to become a potential alternative to conventional antibiotics against bacteria and fungi associated with gastroenteritis.

The specificity of protection against cationic antimicrobial peptides by lactoferrin binding protein B

A variety of Gram-negative pathogens possess host-specific lactoferrin (Lf) receptors that mediate the acquisition of iron from host Lf. The integral membrane protein component of the receptor, lactoferrin binding protein A specifically binds host Lf and is required for acquisition of iron from Lf. In contrast, the role of the bi-lobed surface lipoprotein, lactoferrin binding protein B (LbpB), in Lf binding and iron acquisition is uncertain. A common feature of LbpBs from most species is the presence of clusters of negatively charged amino acids in the protein's C-terminal lobe. Recently it has been shown that the negatively charged regions from the Neisseria meningitidis LbpB are responsible for protecting against an 11 amino acid cationic antimicrobial peptide (CAP), lactoferricin (Lfcin), derived from human Lf. In this study we investigated whether the LbpB confers resistance to other CAPs since N. meningitidis is likely to encounter other CAPs from the host. LbpB provided protection against the cathelicidin derived peptide, cathelicidin related antimicrobial peptide (mCRAMP), but did not confer protection against Tritrp 1 or LL37 under our experimental conditions. When tested against a range of rationally designed synthetic peptides, LbpB was shown to protect against IDR-1002 and IDR-0018 but not against HH-2 or HHC10.