The effect of acidic residues and amphipathicity on the lytic activities of mastoparan peptides studied by fluorescence and CD spectroscopy

Structure modification of anoplin for fighting resistant bacteria

The emergence of bacterial resistance has posed a significant challenge to clinical antimicrobial treatment, rendering commonly used antibiotics ineffective. The development of novel antimicrobial agents and strategies is imperative for the treatment of resistant bacterial infections. Antimicrobial peptides (AMPs) are considered a promising class of antimicrobial agents due to their low propensity for resistance and broad-spectrum activity. Anoplin is a small linear α-helical natural antimicrobial peptide that was isolated from the venom of the solitary wasp Anplius samariensis. It exhibits rich biological activity, particularly broad-spectrum antimicrobial activity and low hemolytic activity. Over the past three decades, more than 40 research publications on anoplin have been made available online. This review focuses on the advancements of anoplin in antimicrobial research, encompassing its sources, characterization, antimicrobial activity, influencing factors and structural modifications. The aim is to provide assistances for the development of new antimicrobial agents that can combat bacterial resistance.

Unwrapping the structural and functional features of antimicrobial peptides from wasp venoms

The study of wasp venoms has captured attention due to the presence of a wide variety of active compounds, revealing a diverse array of biological effects. Among these compounds, certain antimicrobial peptides (AMPs) such as mastoparans and chemotactic peptides have emerged as significant players, characterized by their unique amphipathic short linear alpha-helical structure. These peptides exhibit not only antibiotic properties but also a range of other biological activities, which are related to their ability to interact with biological membranes to varying degrees. This review article aims to provide updated insights into the structure/function relationships of AMPs derived from wasp venoms, linking this knowledge to the potential development of innovative treatments against infections.

Probing Mastoparan-like Antimicrobial Peptides Interaction with Model Membrane Through Energy Landscape Analysis

Antimicrobial Peptides (AMPs) have emerged as promising alternatives to conventional antibiotics due to their capacity to disrupt the lipid packing of bacterial cell membranes. This mechanism of action may prevent the development of resistance by bacteria. Understanding their role in lipid packing disruption and their structural properties upon interaction with bacterial membranes is highly desirable. In this study, we employed Molecular Dynamics simulations and the Energy Landscape Visualization Method (ELViM) to characterize and compare the conformational ensembles of mastoparan-like Polybia-MP1 and its analogous H-MP1, in which histidines replace lysine residues. Two situations were analyzed: (i) the peptides in their free state in an aqueous solution containing water and ions and (ii) the peptides spontaneously adsorbing onto an anionic lipid bilayer, used as a bacteria membrane mimetic. ELViM was used to project a single effective conformational phase space for both peptides, providing a comparative analysis. This projection enabled us to map the conformational ensembles of each peptide in an aqueous solution and assess the structural effects of substituting lysines with histidines in H-MP1. Furthermore, a single conformational phase space analysis was employed to describe structural changes during the adsorption process using the same framework. We show that ELViM provides a comprehensive analysis, able to identify discrepancies in the conformational ensembles of these peptides that may affect their affinity to the membrane and adsorption kinetics.

Effect of substituting glutamine with lysine on structural and biological properties of antimicrobial peptide Polybia-MP1

The natural antimicrobial peptide Polybia-MP1 is a promising candidate for developing new treatment therapy for infection and cancer. It showed broad-spectrum antimicrobial and anticancer activity with high safety on healthy cells. However, previous sequence modification usually resulted in at least one of two consequences: a notable increase in hemolytic activity or a considerable decrease in activity against Gram-negative bacteria and cancer cells. Herein, a new approach was applied by replacing the amino acid Glutamine at position 12 with Lysine and generating the MP1-Q12K analog. Our preliminary data suggested an enhancement in antibacterial and antifungal activity, whereas the anticancer and hemolytic activity of the two peptides were comparable. Moreover, MP1-Q12K was found to be less self-assembly than Polybia-MP1, which further supports the enhancement of antimicrobial properties. Hence, this study provides new information regarding the structure-activity relationships of Polybia-MP1 and support for the development of potent, selective antimicrobial peptides.

Rational design of stapled antimicrobial peptides

The global increase in antimicrobial drug resistance has dramatically reduced the effectiveness of traditional antibiotics. Structurally diverse antibiotics are urgently needed to combat multiple-resistant bacterial infections. As part of innate immunity, antimicrobial peptides have been recognized as the most promising candidates because they comprise diverse sequences and mechanisms of action and have a relatively low induction rate of resistance. However, because of their low chemical stability, susceptibility to proteases, and high hemolytic effect, their usage is subject to many restrictions. Chemical modifications such as D-amino acid substitution, cyclization, and unnatural amino acid modification have been used to improve the stability of antimicrobial peptides for decades. Among them, a side-chain covalent bridge modification, the so-called stapled peptide, has attracted much attention. The stapled side-chain bridge stabilizes the secondary structure, induces protease resistance, and increases cell penetration and biological activity. Recent progress in computer-aided drug design and artificial intelligence methods has also been used in the design of stapled antimicrobial peptides and has led to the successful discovery of many prospective peptides. This article reviews the possible structure-activity relationships of stapled antimicrobial peptides, the physicochemical properties that influence their activity (such as net charge, hydrophobicity, helicity, and dipole moment), and computer-aided methods of stapled peptide design. Antimicrobial peptides under clinical trial: Pexiganan (NCT01594762, 2012-05-07). Omiganan (NCT02576847, 2015-10-13).

An Overview of the Potentialities of Antimicrobial Peptides Derived from Natural Sources

Antimicrobial peptides (AMPs) are constituents of the innate immune system in every kind of living organism. They can act by disrupting the microbial membrane or without affecting membrane stability. Interest in these small peptides stems from the fear of antibiotics and the emergence of microorganisms resistant to antibiotics. Through membrane or metabolic disruption, they defend an organism against invading bacteria, viruses, protozoa, and fungi. High efficacy and specificity, low drug interaction and toxicity, thermostability, solubility in water, and biological diversity suggest their applications in food, medicine, agriculture, animal husbandry, and aquaculture. Nanocarriers can be used to protect, deliver, and improve their bioavailability effectiveness. High cost of production could limit their use. This review summarizes the natural sources, structures, modes of action, and applications of microbial peptides in the food and pharmaceutical industries. Any restrictions on AMPs' large-scale production are also taken into consideration.

Anticancer peptides mechanisms, simple and complex

Peptide therapy has started since 1920s with the advent of insulin application, and now it has emerged as a new approach in treatment of diseases including cancer. Using anti-cancer peptides (ACPs) is a promising way of cancer therapy as ACPs are continuing to be approved and arrived at major pharmaceutical markets. Traditional cancer treatments face different problems like intensive adverse effects to patient's body, cell resistance to conventional chemical drugs and in some worse cases the occurrence of cell multidrug resistance (MDR) of cancerous tissues against chemotherapy. On the other hand, there are some benefits conceived for peptides usage in treatment of diseases specifically cancer, as these compounds present favorable characteristics such as smaller size, high activity, low immunogenicity, good biocompatibility in vivo, convenient and rapid way of synthesis, amenable to sequence modification and revision and there is no limitation for the type of cargo they carry. It is possible to achieve an optimum molecular and functional structure of peptides based on previous experience and bank of peptide motif data which may result in novel peptide design. Bioactive peptides are able to form pores in cell membrane and induce necrosis or apoptosis of abnormal cells. Moreover, recent researches have focused on the tumor recognizing peptide motifs with the ability to permeate to cancerous cells with the aim of cancer treatment at earlier stages. In this strategy the most important factors for addressing cancer are choosing peptides with easy accessibility to tumor cell without cytotoxicity effect towards normal cells. The peptides must also meet acceptable pharmacokinetic requirements. In this review, the characteristics of peptides and cancer cells are discussed. The various mechanisms of peptides' action proposed against cancer cells make the next part of discussion. It will be followed by giving information on peptides application, various methods of peptide designing along with introducing various databases. Future aspects of peptides for employing in area of cancer treatment come as conclusion at the end.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

The Antimicrobial Peptide Mastoparan X Protects Against Enterohemorrhagic Escherichia coli O157:H7 Infection, Inhibits Inflammation, and Enhances the Intestinal Epithelial Barrier

Escherichia coli can cause intestinal diseases in humans and livestock, destroy the intestinal barrier, exacerbate systemic inflammation, and seriously threaten human health and animal husbandry development. The aim of this study was to investigate whether the antimicrobial peptide mastoparan X (MPX) was effective against E. coli infection. BALB/c mice infected with E. coli by intraperitoneal injection, which represents a sepsis model. In this study, MPX exhibited no toxicity in IPEC-J2 cells and notably suppressed the levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), myeloperoxidase (MPO), and lactate dehydrogenase (LDH) released by E. coli. In addition, MPX improved the expression of ZO-1, occludin, and claudin and enhanced the wound healing of IPEC-J2 cells. The therapeutic effect of MPX was evaluated in a murine model, revealing that it protected mice from lethal E. coli infection. Furthermore, MPX increased the length of villi and reduced the infiltration of inflammatory cells into the jejunum. SEM and TEM analyses showed that MPX effectively ameliorated the jejunum damage caused by E. coli and increased the number and length of microvilli. In addition, MPX decreased the expression of IL-2, IL-6, TNF-α, p-p38, and p-p65 in the jejunum and colon. Moreover, MPX increased the expression of ZO-1, occludin, and MUC2 in the jejunum and colon, improved the function of the intestinal barrier, and promoted the absorption of nutrients. This study suggests that MPX is an effective therapeutic agent for E. coli infection and other intestinal diseases, laying the foundation for the development of new drugs for bacterial infections.

Strategies towards Targeting Gαi/s Proteins: Scanning of Protein-Protein Interaction Sites To Overcome Inaccessibility

Heterotrimeric G proteins are classified into four subfamilies and play a key role in signal transduction. They transmit extracellular signals to intracellular effectors subsequent to the activation of G protein-coupled receptors (GPCRs), which are targeted by over 30 % of FDA-approved drugs. However, addressing G proteins as drug targets represents a compelling alternative, for example, when G proteins act independently of the corresponding GPCRs, or in cases of complex multifunctional diseases, when a large number of different GPCRs are involved. In contrast to Gαq, efforts to target Gαi/s by suitable chemical compounds has not been successful so far. Here, a comprehensive analysis was conducted examining the most important interface regions of Gαi/s with its upstream and downstream interaction partners. By assigning the existing compounds and the performed approaches to the respective interfaces, the druggability of the individual interfaces was ranked to provide perspectives for selective targeting of Gαi/s in the future.

Oriental Hornet (Vespa orientalis) Larval Extracts Induce Antiproliferative, Antioxidant, Anti-Inflammatory, and Anti-Migratory Effects on MCF7 Cells

The use of insects as a feasible and useful natural product resource is a novel and promising option in alternative medicine. Several components from insects and their larvae have been found to inhibit molecular pathways in different stages of cancer. This study aimed to analyze the effect of aqueous and alcoholic extracts of Vespa orientalis larvae on breast cancer MCF7 cells and investigate the underlying mechanisms. Our results showed that individual treatment with 5% aqueous or alcoholic larval extract inhibited MCF7 proliferation but had no cytotoxic effect on normal Vero cells. The anticancer effect was mediated through (1) induction of apoptosis, as indicated by increased expression of apoptotic genes (Bax, caspase3, and p53) and decreased expression of the anti-apoptotic gene Bcl2; (2) suppression of intracellular reactive oxygen species; (3) elevation of antioxidant enzymes (CAT, SOD, and GPx) and upregulation of the antioxidant regulator Nrf2 and its downstream target HO-1; (4) inhibition of migration as revealed by in vitro wound healing assay and downregulation of the migration-related gene MMP9 and upregulation of the anti-migratory gene TIMP1; and (5) downregulation of inflammation-related genes (NFκB and IL8). The aqueous extract exhibited the best anticancer effect with higher antioxidant activities but lower anti-inflammatory properties than the alcoholic extract. HPLC analysis revealed the presence of several flavonoids and phenolic compounds with highest concentrations for resveratrol and naringenin in aqueous extract and rosmarinic acid in alcoholic extract. This is the first report to explain the intracellular pathway by which flavonoids and phenolic compounds-rich extracts of Vespa orientalis larvae could induce MCF7 cell viability loss through the initiation of apoptosis, activation of antioxidants, and inhibition of migration and inflammation. Therefore, these extracts could be used as adjuvants for anticancer drugs and as antioxidant and anti-inflammatory agents.

Modulatory Effects of Acidic pH and Membrane Potential on the Adsorption of pH-Sensitive Peptides to Anionic Lipid Membrane

Anionic lipid membrane electrostatic potential and solution pH can influence cationic peptide adsorption to these bilayers, especially those containing simultaneously acid and basic residues. Here, we investigate the effects of the pH solution on MP1 (IDWKKLLDAAKQIL-NH2) adsorption to anionic (7POPC:3POPG) lipid vesicles in comparison to its analog H-MP1, with histidines substituting lysines. We used the association of adsorption isotherms and constant pH molecular dynamic simulations (CpHMD) to explore the effects of membrane potential and pH on peptides' adsorption on this lipid membrane. We analyzed the fluorescence and zeta potential adsorption isotherms using the Gouy-Chapman theory. In CpHMD simulations for the peptides in solution and adsorbed on the lipid bilayer, we used the conformations obtained by conventional MD simulations at a μs timescale. Non-equilibrium Monte Carlo simulations provided the protonation states of acidic and basic residues. CpHMD showed average pKa shifts of two to three units, resulting in a higher net charge for the analog than for MP1, strongly modulating the peptide adsorption. The fractions of the protonation of acidic and basic residues and the peptides' net charges obtained from the analysis of the adsorption isotherms were in reasonable agreement with those from CpHMD. MP1 adsorption was almost insensitive to solution pH. H-MP1 was much more sensitive to partitioning, at acidic pH, with an affinity ten times higher than in neutral ones.

Antimicrobial peptides - Advances in development of therapeutic applications

The severe infection is becoming a significant health problem which threaten the lives of patients and the safety and economy of society. In the way of finding new strategy, antimicrobial peptides (AMPs) - an important part of host defense family, emerged with tremendous potential. Up to date, huge numbers of AMPs has been investigated from both natural and synthetic sources showing not only the ability to kill microbial pathogens but also propose other benefits such as wound healing, anti-tumor, immune modulation. In this review, we describe the involvements of AMPs in biological systems and discuss the opportunity in developing AMPs for clinical applications. In the detail, their properties in antibacterial activity is followed by their application in some infection diseases and cancer. The key discussions are the approaches to improve biological activities of AMPs either by modifying chemical structure or incorporating into delivery systems. The new applications and perspectives for the future of AMPs would open the new era of their development.

The antimicrobial peptide MPX kills Actinobacillus pleuropneumoniae and reduces its pathogenicity in mice

Actinobacillus pleuropneumoniae is the causative agent of highly contagious and fatal respiratory infections, causing substantial economic losses to the global pig industry. Due to increased antibiotic resistance, there is an urgent need to find new antibiotic alternatives for treating A. pleuropneumoniae infections. MPX is obtained from wasp venom and has a killing effect on various bacteria. This study found that MPX had a good killing effect on A. pleuropneumoniae and that the minimum inhibitory concentration (MIC) was 16 μg/mL. The bacterial density of A. pleuropneumoniae decreased 1000 times after MPX (1 × MIC) treatment for 1 h, and the antibacterial activity was not affected by pH or temperature. Fluorescence microscopy showed that MPX (1 × MIC) destroyed the bacterial cell membrane after treatment for 0.5 h, increasing membrane permeability and releasing bacterial proteins and Ca²⁺, Na⁺ and other cations. In addition, MPX (1 × MIC) treatment significantly reduced the formation of bacterial biofilms. Quantitative RT-PCR results showed that MPX treatment significantly upregulated the expression of the PurC virulence gene and downregulated that of ApxI, ApxII, and Apa1. In addition, the Sap A gene was found to play an important role in the tolerance of A. pleuropneumoniae to antimicrobial peptides. Therapeutic evaluation in a murine model showed that MPX protects mice from a lethal dose of A. pleuropneumoniae and relieves lung inflammation. This study reports the use of MPX to treat A. pleuropneumonia infections, laying the foundation for the development of new drugs for bacterial infections.

Metal self-assembly mimosine peptides with enhanced antimicrobial activity: towards a new generation of multitasking chelating agents

Mimosine is a non-protein amino acid that can be used as a building block in peptides with metal coordination ability.

Chemical and Biological Characteristics of Antimicrobial α-Helical Peptides Found in Solitary Wasp Venoms and Their Interactions with Model Membranes

Solitary wasps use their stinging venoms for paralyzing insect or spider prey and feeding them to their larvae. We have surveyed bioactive substances in solitary wasp venoms, and found antimicrobial peptides together with some other bioactive peptides. Eumenine mastoparan-AF (EMP-AF) was the first to be found from the venom of the solitary eumenine wasp Anterhynchium flavomarginatum micado, showing antimicrobial, histamine-releasing, and hemolytic activities, and adopting an α-helical secondary structure under appropriate conditions. Further survey of solitary wasp venom components revealed that eumenine wasp venoms contained such antimicrobial α-helical peptides as the major peptide component. This review summarizes the results obtained from the studies of these peptides in solitary wasp venoms and some analogs from the viewpoint of (1) chemical and biological characterization; (2) physicochemical properties and secondary structure; and (3) channel-like pore-forming properties.

Antimicrobial peptides: Promising alternatives in the post feeding antibiotic era

Antimicrobial peptides (AMPs), critical components of the innate immune system, are widely distributed throughout the animal and plant kingdoms. They can protect against a broad array of infection-causing agents, such as bacteria, fungi, parasites, viruses, and tumor cells, and also exhibit immunomodulatory activity. AMPs exert antimicrobial activities primarily through mechanisms involving membrane disruption, so they have a lower likelihood of inducing drug resistance. Extensive studies on the structure-activity relationship have revealed that net charge, hydrophobicity, and amphipathicity are the most important physicochemical and structural determinants endowing AMPs with antimicrobial potency and cell selectivity. This review summarizes the recent advances in AMPs development with respect to characteristics, structure-activity relationships, functions, antimicrobial mechanisms, expression regulation, and applications in food, medicine, and animals.

The effect of pH on the lytic activity of a synthetic mastoparan-like peptide in anionic model membranes

Peptide sequences containing acidic and basic residues could potentially have their net charges modulated by bulk pH with a possible influence on their lytic activity in lipid vesicles. The present study reports on a biophysical investigation of these modulatory effects on the synthetic mastoparan-like peptide L1A (IDGLKAIWKKVADLLKNT-NH2). At pH 10.0 L1A was 6 times more efficient in lysing large anionic (1-palmitoyl-oleoyl-sn-glycero-3-phosphocholine (POPC):1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG)/(8:2)) unilamellar vesicles (LUVs) than at pH 4.0. Despite the reduction of 60% in the L1A net charge in basic pH its affinity for this vesicle was almost insensitive to pH. On the other hand, L1A insertion into monolayers was dramatically influenced by subphase condition, showing that, in the neutral and basic subphases, the peptide induced surface pressure changes that surpassed the membrane lateral pressure, being able to destabilize a bilayer structure. In addition, in the basic subphase, visualization of the compression isotherms of co-spread 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC):POPG (8:2) + 4.8 mol% L1A showed that the peptide induced significant changes in solid lipid domains, indicating its capability in perturbing lipid-packing. An insight into L1A lytic activity was also obtained in giant unilamellar vesicles (GUVs) using phase contrast microscopy. The suppression of L1A lytic activity at acidic pH is in keeping with its lower insertion capability and ability to disturb the lipid monolayer. The lytic activity observed under neutral and basic conditions showed a quick and stochastic leakage following a lag-time. The permeability and the leakage-time averaged over at least 14 single GUVs were dependent on the bulk condition. At basic pH, permeability is higher and quicker than in a neutral medium in good accordance with the lipid-packing perturbation.

Recent Advances in Antibacterial and Antiendotoxic Peptides or Proteins from Marine Resources

Infectious diseases caused by Gram-negative bacteria and sepsis induced by lipopolysaccharide (LPS) pose a major threat to humans and animals and cause millions of deaths each year. Marine organisms are a valuable resource library of bioactive products with huge medicinal potential. Among them, antibacterial and antiendotoxic peptides or proteins, which are composed of metabolically tolerable residues, are present in many marine species, including marine vertebrates, invertebrates and microorganisms. A lot of studies have reported that these marine peptides and proteins or their derivatives exhibit potent antibacterial activity and antiendotoxic activity in vitro and in vivo. However, their categories, heterologous expression in microorganisms, physicochemical factors affecting peptide or protein interactions with bacterial LPS and LPS-neutralizing mechanism are not well known. In this review, we highlight the characteristics and anti-infective activity of bifunctional peptides or proteins from marine resources as well as the challenges and strategies for further study.

Effect of N-terminal acetylation on lytic activity and lipid-packing perturbation induced in model membranes by a mastoparan-like peptide

L1A (IDGLKAIWKKVADLLKNT-NH2) is a peptide that displays a selective antibacterial activity to Gram-negative bacteria without being hemolytic. Its lytic activity in anionic lipid vesicles was strongly enhanced when its N-terminus was acetylated (ac-L1A). This modification seems to favor the perturbation of the lipid core of the bilayer by the peptide, resulting in higher membrane lysis. In the present study, we used lipid monolayers and bilayers as membrane model systems to explore the impact of acetylation on the L1A lytic activity and its correlation with lipid-packing perturbation. The lytic activity investigated in giant unilamellar vesicles (GUVs) revealed that the acetylated peptide permeated the membrane at higher rates compared with L1A, and modified the membrane's mechanical properties, promoting shape changes. The peptide secondary structure and the changes in the environment of the tryptophan upon adsorption to large unilamellar vesicles (LUVs) were monitored by circular dichroism (CD) and red-edge excitation shift experiments (REES), respectively. These experiments showed that the N-terminus acetylation has an important effect on both, peptide secondary structure and peptide insertion into the bilayer. This was also confirmed by experiments of insertion into lipid monolayers. Compression isotherms for peptide/lipid mixed films revealed that ac-L1A dragged lipid molecules to the more disordered phase, generating a more favorable environment and preventing the lipid molecules from forming stiff films. Enthalpy changes in the main phase transition of the lipid membrane upon peptide insertion suggested that the acetylated peptide induced higher impact than the non-acetylated one on the thermotropic behavior of anionic vesicles.

Lipid-packing perturbation of model membranes by pH-responsive antimicrobial peptides

The indiscriminate use of conventional antibiotics is leading to an increase in the number of resistant bacterial strains, motivating the search for new compounds to overcome this challenging problem. Antimicrobial peptides, acting only in the lipid phase of membranes without requiring specific membrane receptors as do conventional antibiotics, have shown great potential as possible substituents of these drugs. These peptides are in general rich in basic and hydrophobic residues forming an amphipathic structure when in contact with membranes. The outer leaflet of the prokaryotic cell membrane is rich in anionic lipids, while the surface of the eukaryotic cell is zwitterionic. Due to their positive net charge, many of these peptides are selective to the prokaryotic membrane. Notwithstanding this preference for anionic membranes, some of them can also act on neutral ones, hampering their therapeutic use. In addition to the electrostatic interaction driving peptide adsorption by the membrane, the ability of the peptide to perturb lipid packing is of paramount importance in their capacity to induce cell lysis, which is strongly dependent on electrostatic and hydrophobic interactions. In the present research, we revised the adsorption of antimicrobial peptides by model membranes as well as the perturbation that they induce in lipid packing. In particular, we focused on some peptides that have simultaneously acidic and basic residues. The net charges of these peptides are modulated by pH changes and the lipid composition of model membranes. We discuss the experimental approaches used to explore these aspects of lipid membranes using lipid vesicles and lipid monolayer as model membranes.

Polydim-I antimicrobial activity against MDR bacteria and its model membrane interaction

The rapid spread of multi-drug resistant pathogens represents a serious threat to public health, considering factors such as high mortality rates, treatment restrictions and high prevalence of multi-drug resistant bacteria in the hospital environment. Antimicrobial peptides (AMPs) may exhibit powerful antimicrobial activity against different and diverse microorganisms, also presenting the advantage of absence or low toxicity towards animal cells. In this study, the evaluation of the antimicrobial activity against multi-drug resistant bacteria of a recently described AMP from wasp, Polydim-I, was performed. Polydim-I presented activity against standard strains (non-carriers of multi-resistant genes) that are susceptible to commercial antimicrobials, and also against multi-drug resistant strains at concentrations bellow 1μg/ml (0.41 μM). This is a rather low concentration among those reported for AMPs. At this concentration we found out that Polydim-I inhibits almost 100% of the tested pathogens growth, while with the ATCC strains the minimum inhibitory concentration (MIC₁₀₀) is 400 times higher. Also, in relation to in vitro activity of conventional drugs against multi-drug resistant bacteria strains, Polydim-I is almost 10 times more efficient and with broader spectrum. Cationic AMPs are known as multi-target compounds and specially for targeting the phospholipid matrix of bacterial membranes. Exploring the interactions of Polydim-I with lipid bilayers, we have confirmed that this interaction is involved in the mechanism of action. Circular dichroism experiments showed that Polydim-I undergoes a conformational transition from random coil to a mostly helical conformation in the presence of membrane mimetic environments. Zeta potential measurements confirmed the binding and partial charge neutralization of anionic asolectin vesicles, and also suggested a possible aggregation of peptide molecules. FTIR experiments confirmed that some peptide aggregation occurs, which is minimized in the presence of strongly anionic micelles of sodium dodecyl sulfate. Also, Polydim-I induced channel-like structures formation to asolectin lipid bilayers, as demonstrated in the electrophysiology experiments. We suggest that cationic Polydim-I targets the membrane lipids due to electrostatic attraction, partially accumulates, neutralizing the opposite charges and induces pore formation. Similar mechanism of action has already been suggested for other peptides from wasp venoms, especially mastoparans.

MD simulations and multivariate studies for modeling the antileishmanial activity of peptides

Leishmaniasis, a protozoan-caused disease, requires alternative treatments with minimized side-effects and less prone to resistance development. Antimicrobial peptides represent a possible choice to be developed. We report on the prospection of structural parameters of 23 helical antimicrobial and leishmanicidal peptides as a tool for modeling and predicting the activity of new peptides. This investigation is based on molecular dynamic simulations (MD) in mimetic membrane environment, as most of these peptides share the feature of interacting with phospholipid bilayers. To overcome the lack of experimental data on peptides' structures, we started simulations from designed 100% α-helices. This procedure was validated through comparisons with NMR data and the determination of the structure of Decoralin-amide. From physicochemical features and MD results, descriptors were raised and statistically related to the minimum inhibitory concentration against Leishmania by the multivariate data analysis technique. This statistical procedure confirmed five descriptors combined by different loadings in five principal components. The leishmanicidal activity depends on peptides' charge, backbone solvation, volume, and solvent-accessible surface area. The generated model possesses good predictability (q²  = 0.715, r²  = 0.898) and is indicative for the most and the least active peptides. This is a novel theoretical path for structure-activity studies combining computational methods that identify and prioritize the promising peptide candidates.

Phosphatidylserine lipids and membrane order precisely regulate the activity of Polybia-MP1 peptide

Polybia-MP1 (IDWKKLLDAAKQIL-NH₂) is a lytic peptide from the Brazilian wasp venom with known anti-cancer properties. Previous evidence indicates that phosphatidylserine (PS) lipids are relevant for the lytic activity of MP1. In agreement with this requirement, phosphatidylserine lipids are translocated to the outer leaflet of cells, and are available for MP1 binding, depending on the presence of liquid-ordered domains. Here, we investigated the effect of PS on MP1 activity when this lipid is reconstituted in membranes of giant or large liposomes with different lipid-phase states. By monitoring the membrane and soluble luminal content of giant unilamellar vesicles (GUVs), using fluorescence confocal microscopy, we were able to determine that MP1 has a pore-forming activity at the membrane level. Liquid-ordered domains, which were phase-separated within the membrane of GUVs, influenced the pore-forming activity of MP1. Experiments evaluating the membrane-binding and lytic activity of MP1 on large unilamellar vesicles (LUVs), with the same lipid composition as GUVs, demonstrated that there was synergy between liquid-ordered domains and PS, which enhanced both activities. Based on our findings, we propose that the physicochemical properties of cancer cell membranes, which possess a much higher concentration of PS than normal cells, renders them susceptible to MP1 binding and lytic pore formation. These results can be correlated with MP1's potent and selective anti-cancer activity and pave the way for future research to develop cancer therapies that harness and exploit the properties of MP1.

Antiviral activity of animal venom peptides and related compounds

Viruses exhibit rapid mutational capacity to trick and infect host cells, sometimes assisted through virus-coded peptides that counteract host cellular immune defense. Although a large number of compounds have been identified as inhibiting various viral infections and disease progression, it is urgent to achieve the discovery of more effective agents. Furthermore, proportionally to the great variety of diseases caused by viruses, very few viral vaccines are available, and not all are efficient. Thus, new antiviral substances obtained from natural products have been prospected, including those derived from venomous animals. Venoms are complex mixtures of hundreds of molecules, mostly peptides, that present a large array of biological activities and evolved to putatively target the biochemical machinery of different pathogens or host cellular structures. In addition, non-venomous compounds, such as some body fluids of invertebrate organisms, exhibit antiviral activity. This review provides a panorama of peptides described from animal venoms that present antiviral activity, thereby reinforcing them as important tools for the development of new therapeutic drugs.

Effects of N-terminus modifications on the conformation and permeation activities of the synthetic peptide L1A

We investigate the effect of the N-terminus modification of the L1A, a synthetic octadecapeptide, on its helical content, affinity and lytic action in model membranes and on its hemolytic and antibacterial activities. L1A and its acetylated analog displayed a selective antibacterial activity to Gram-negative bacteria without being hemolytic. The covalently linked 2-aminobezoic acid to the N-terminus impaired the antibacterial efficacy and increased hemolysis. Despite their lower net charge (+2), N-terminus modifications resulted in enhanced affinity and improved lytic efficiency in anionic vesicles. The analogs also showed higher helical content and consequently higher amphipathicity in these vesicles. The conformational analysis by molecular dynamics simulations in 30 % of TFE/water showed that the hydrophobic faces of the peptides are in close contact with CF3 groups of TFE while the hydrophilic faces with water molecules. Due to the loss of the amino charge, the N-termini of the analogs are buried in TFE molecules. The analysis of the pair distribution functions, obtained for the center of mass of the charged groups, has evidenced that the state of the N-terminus has influenced the possibility of different ion-pairing. The higher complexity of the bacterial cells compared with anionic vesicles hampers to establish correlations structure-function for the analogs.

Structure-activity relationship of mastoparan analogs: Effects of the number and positioning of Lys residues on secondary structure, interaction with membrane-mimetic systems and biological activity

In this study, a series of mastoparan analogs were engineered based on the strategies of Ala and Lys scanning in relation to the sequences of classical mastoparans. Ten analog mastoparans, presenting from zero to six Lys residues in their sequences were synthesized and assayed for some typical biological activities for this group of peptide: mast cell degranulation, hemolysis, and antibiosis. In relation to mast cell degranulation, the apparent structural requirement to optimize this activity was the existence of one or two Lys residues at positions 8 and/or 9. In relation to hemolysis, one structural feature that strongly correlated with the potency of this activity was the number of amino acid residues from the C-terminus of each peptide continuously embedded into the zwitterionic membrane of erythrocytes-mimicking liposomes, probably due to the contribution of this structural feature to the membrane perturbation. The antibiotic activity of mastoparan analogs was directly dependent on the apparent extension of their hydrophilic surface, i.e., their molecules must have from four to six Lys residues between positions 4 and 11 of the peptide chain to achieve activities comparable to or higher than the reference antibiotic compounds. The optimization of the antibacterial activity of the mastoparans must consider Lys residues at the positions 4, 5, 7, 8, 9, and 11 of the tetradecapeptide chain, with the other positions occupied by hydrophobic residues, and with the C-terminal residue in the amidated form. These requirements resulted in highly active AMPs with greatly reduced (or no) hemolytic and mast cell degranulating activities.

Characterization of antimicrobial activity and mechanisms of low amphipathic peptides with different α-helical propensity

Antimicrobial peptides (AMPs) serve as a defense mechanism within multicellular organisms and are attracting increasing attention because of their potential application in the treatment of multidrug-resistant infections. Amphipathicity has long been believed to be the most important consideration for the structural modification and design of both naturally occurring and synthetic AMPs. Previous studies indicated that disruptive amphipathicity formed by replacing the paired charged amino acid residues on the polar face of an amphipathic helix with tryptophan residues linked with hydrogen bonds on the basis of α-helical protein folding principles endowed the AMPs with increased cell selectivity. In an attempt to augment and hone this strategy further, we designed a series of imperfect amphipathic peptides by placing different types of amino acid residues at the hydrogen bond linked positions of α-helix structures to characterize their antimicrobial properties and mechanism of action. The d-Trp-substituted sequence (PRW4-d) showed greater antimicrobial potency than Cys-(C4), Asp-(D4), Ile-(I4), and Pro-(P4) substituted sequences, comparable to the l-Trp-substituted parent sequence (PRW4). Furthermore, the total replacement of Lys residues with Arg residues along the peptide sequence (PRW4-R) exhibited enhanced antimicrobial activity and cell selectivity. In addition, no cytotoxicity was observed among these synthetic peptides. PRW4-d and PRW4-R maintained their activities in the presence of physiological salts and human serum. The fluorescence spectroscopy, flow cytometry, and electron microscopy observations indicated that the optimized sequences exhibited excellent antimicrobial potency by inducing cytoplasmic membrane potential loss, membrane permeabilization and disruption. Collectively, the results could be useful for designing short AMPs with great antimicrobial activity and cell selectivity.

Three valuable peptides from bee and wasp venoms for therapeutic and biotechnological use: melittin, apamin and mastoparan

While knowledge of the composition and mode of action of bee and wasp venoms dates back 50 years, the therapeutic value of these toxins remains relatively unexploded. The properties of these venoms are now being studied with the aim to design and develop new therapeutic drugs. Far from evaluating the extensive number of monographs, journals and books related to bee and wasp venoms and the therapeutic effect of these toxins in numerous diseases, the following review focuses on the three most characterized peptides, namely melittin, apamin, and mastoparan. Here, we update information related to these compounds from the perspective of applied science and discuss their potential therapeutic and biotechnological applications in biomedicine.

Effect of the aspartic acid D2 on the affinity of Polybia-MP1 to anionic lipid vesicles

Polybia-MP1 (IDWKKLLDAAKQIL-NH2), a helical peptide extracted from the venom of a Brazilian wasp, has broad-spectrum antimicrobial activities without being hemolytic or cytotoxic. This peptide has also displayed anticancer activity against cancer cell cultures. Despite its high selectivity, MP1 has an unusual low net charge (Q = +2). The aspartic residue (D2) in the N-terminal region plays an important role in its affinity and selectivity; its substitution by asparagine (D2N mutant) led to a less selective peptide. Aiming to explore the importance of this residue for the peptides' affinity, we compared the zwitterionic and anionic vesicle adsorption activity of Polybia-MP1 versus its D2N mutant and also mastoparan X (MPX). The adsorption, electrostatic, and conformational free energies were assessed by circular dichroism (CD) and fluorescence titrations using large unilamellar vesicles (LUVs) at the same conditions in association with measurement of the zeta potential of LUVs in the presence of the peptides. The adsorption free energies of the peptides, determined from the partition coefficients, indicated higher affinity of MP1 to anionic vesicles compared with the D2N mutant and MPX. The electrostatic and conformational free energies of MP1 in anionic vesicles are less favorable than those found for the D2N mutant and MPX. Therefore, the highest affinity of MP1 to anionic vesicles is likely due to other energetic contributions. The presence of D2 in MP1 makes these energetic components 1.2 and 1.5 kcal/mol more favorable compared with the D2N mutant and MPX, respectively.

New insight into the mechanism of action of wasp mastoparan peptides: lytic activity and clustering observed with giant vesicles

Antimicrobial peptides of the mastoparans family exert their bactericidal activity by binding to lipid membranes, inducing pores or defects and leaking the internal contents of vesicles and cells. However, this does not seem to be the only mechanism at play, and they might be important in the search for improved peptides with lower undesirable side effects. This work deals with three mastoparans peptides, Polybia-MP-1(MP-1), N2-Polybia-MP-1 (N-MP-1), and Mastoparan X (MPX), which exhibit high sequence homology. They all have three lysine residues and amidated C termini, but because of the presence of two, one, and no aspartic acid residues, respectively, they have +2, +3, and +4 net charges at physiological pH. Here we focus on the effects of these mastoparans peptides on anionic model membranes made of palmitoleyoilphosphatidylcholine (POPC) and palmitoleyoilphosphatidylglycerol (POPG) at 1:1 and 3:1 molar ratios in the presence and in the absence of saline buffer. Zeta potential experiments were carried out to measure the extent of the peptides' binding and accumulation at the vesicle surface, and CD spectra were acquired to quantify the helical structuring of the peptides upon binding. Giant unilamellar vesicles were observed under phase contrast and fluorescence microscopy. We found that the three peptides induced the leakage of GUVs at a gradual rate with many characteristics of the graded mode. This process was faster in the absence of saline buffer. Additionally, we observed that the peptides induced the formation of dense regions of phospholipids and peptides on the GUV surface. This phenomenon was easily observable for the more charged peptides (MPX > N-MP-1 > MP-1) and in the absence of added salt. Our data suggest that these mastoparans accumulate on the bilayer surface and induce a transient interruption to its barrier properties, leaking the vesicle contents. Next, the bilayer recovers its continuity, but this happens in an inhomogeneous way, forming a kind of ply with peptides sandwiched between two juxtaposed membranes. Eventually, a peptide-lipid aggregate forming a lump is formed at high peptide-to-lipid ratios.

Chemometric analysis of Hymenoptera toxins and defensins: A model for predicting the biological activity of novel peptides from venoms and hemolymph

When searching for prospective novel peptides, it is difficult to determine the biological activity of a peptide based only on its sequence. The "trial and error" approach is generally laborious, expensive and time consuming due to the large number of different experimental setups required to cover a reasonable number of biological assays. To simulate a virtual model for Hymenoptera insects, 166 peptides were selected from the venoms and hemolymphs of wasps, bees and ants and applied to a mathematical model of multivariate analysis, with nine different chemometric components: GRAVY, aliphaticity index, number of disulfide bonds, total residues, net charge, pI value, Boman index, percentage of alpha helix, and flexibility prediction. Principal component analysis (PCA) with non-linear iterative projections by alternating least-squares (NIPALS) algorithm was performed, without including any information about the biological activity of the peptides. This analysis permitted the grouping of peptides in a way that strongly correlated to the biological function of the peptides. Six different groupings were observed, which seemed to correspond to the following groups: chemotactic peptides, mastoparans, tachykinins, kinins, antibiotic peptides, and a group of long peptides with one or two disulfide bonds and with biological activities that are not yet clearly defined. The partial overlap between the mastoparans group and the chemotactic peptides, tachykinins, kinins and antibiotic peptides in the PCA score plot may be used to explain the frequent reports in the literature about the multifunctionality of some of these peptides. The mathematical model used in the present investigation can be used to predict the biological activities of novel peptides in this system, and it may also be easily applied to other biological systems.