Activity of two synthetic amphiphilic peptides and magainin-2 against herpes simplex virus types 1 and 2

A Review of the Antiviral Activity of Cationic Antimicrobial Peptides

Viral epidemics are occurring frequently, and the COVID-19 viral pandemic has resulted in at least 6.5 million deaths worldwide. Although antiviral therapeutics are available, these may not have sufficient effect. The emergence of resistant or novel viruses requires new therapies. Cationic antimicrobial peptides are agents of the innate immune system that may offer a promising solution to viral infections. These peptides are gaining attention as possible therapies for viral infections or for use as prophylactic agents to prevent viral spread. This narrative review examines antiviral peptides, their structural features, and mechanism of activity. A total of 156 cationic antiviral peptides were examined for information of their mechanism of action against both enveloped and non-enveloped viruses. Antiviral peptides can be isolated from various natural sources or can be generated synthetically. The latter tend to be more specific and effective and can be made to have a broad spectrum of activity with minimal side effects. Their unique properties of being positively charges and amphipathic enable their main mode of action which is to target and disrupt viral lipid envelopes, thereby inhibiting viral entry and replication. This review offers a comprehensive summary of the current understanding of antiviral peptides, which could potentially aid in the design and creation of novel antiviral medications.

Probing the competitive inhibitor efficacy of frog-skin alpha helical AMPs identified against ACE2 binding to SARS-CoV-2 S1 spike protein as therapeutic scaffold to prevent COVID-19

In COVID-19 infection, the SARS-CoV-2 spike protein S1 interacts to the ACE2 receptor of human host, instigating the viral infection. To examine the competitive inhibitor efficacy of broad spectrum alpha helical AMPs extracted from frog skin, a comparative study of intermolecular interactions between viral S1 and AMPs was performed relative to S1-ACE2p interactions. The ACE2 binding region with S1 was extracted as ACE2p from the complex for ease of computation. Surprisingly, the Spike-Dermaseptin-S9 complex had more intermolecular interactions than the other peptide complexes and importantly, the S1-ACE2p complex. We observed how atomic displacements in docked complexes impacted structural integrity of a receptor-binding domain in S1 through conformational sampling analysis. Notably, this geometry-based sampling approach confers the robust interactions that endure in S1-Dermaseptin-S9 complex, demonstrating its conformational transition. Additionally, QM calculations revealed that the global hardness to resist chemical perturbations was found more in Dermaseptin-S9 compared to ACE2p. Moreover, the conventional MD through PCA and the torsional angle analyses indicated that Dermaseptin-S9 altered the conformations of S1 considerably. Our analysis further revealed the high structural stability of S1-Dermaseptin-S9 complex and particularly, the trajectory analysis of the secondary structural elements established the alpha helical conformations to be retained in S1-Dermaseptin-S9 complex, as substantiated by SMD results. In conclusion, the functional dynamics proved to be significant for viral Spike S1 and Dermaseptin-S9 peptide when compared to ACE2p complex. Hence, Dermaseptin-S9 peptide inhibitor could be a strong candidate for therapeutic scaffold to prevent infection of SARS-CoV-2.

Antiviral peptides from aquatic organisms: Functionality and potential inhibitory effect on SARS-CoV-2

Several antiviral peptides (AVPs) from aquatic organisms have been effective in interfering with the actions of infectious viruses, such as Human Immunodeficiency Virus-1 and Herpes Simplex Virus-1 and 2. AVPs are able to block viral attachment or entry into host cells, inhibit internal fusion or replication events by suppressing viral gene transcription, and prevent viral infections by modulating host immunity. Therefore, as promising therapeutics, the potential of aquatic AVPs for use against the COVID-19 pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is considered. At present no therapeutic drugs are yet available. A total of 32 AVPs derived from fish and shellfish species are discussed in this review paper with notes on their properties and mechanisms of action in the inhibition of viral diseases both in humans and animals, emphasizing on SARS-CoV-2. The molecular structure of novel SARS-CoV-2 with its entry mechanisms, clinical signs and symptoms are also discussed. In spite of only a few study of these AVPs against SARS-CoV-2, aquatic AVPs properties and infection pathways (entry, replication and particle release) into coronaviruses are linked in this paper to postulate an analysis of their potential but unconfirmed actions to impair SARS-CoV-2 infection in humans.

Identification of the Active Principle Conferring Anti-Inflammatory and Antinociceptive Properties in Bamboo Plant

Early plants began colonizing earth about 450 million years ago. During the process of coevolution, their metabolic cellular pathways produced a myriad of natural chemicals, many of which remain uncharacterized biologically. Popular preparations containing some of these molecules have been used medicinally for thousands of years. In Brazilian folk medicine, plant extracts from the bamboo plant Guadua paniculata Munro have been used for the treatment of infections and pain. However, the chemical basis of these therapeutic effects has not yet been identified. Here, we performed protein biochemistry and downstream pharmacological assays to determine the mechanisms underlying the anti-inflammatory and antinociceptive effects of an aqueous extract of the G. paniculata rhizome, which we termed AqGP. The anti-inflammatory and antinociceptive effects of AqGP were assessed in mice. We identified and purified a protein (AgGP), with an amino acid sequence similar to that of thaumatins (~20 kDa), capable of repressing inflammation through downregulation of neutrophil recruitment and of decreasing hyperalgesia in mice. In conclusion, we have identified the molecule and the molecular mechanism responsible for the anti-inflammatory and antinociceptive properties of a plant commonly used in Brazilian folk medicine.

Dual antimicrobial and anticancer activity of a novel synthetic α-helical antimicrobial peptide

Antimicrobial peptides (AMPs) are increasingly sought-after and researched antimicrobial agents due to its desired pharmacological properties and the continuous diminishing efficacy of antibiotics. In addition to this line of research, the aim of the present study is to determine the antimicrobial and anticancer activity of a de novo designed α-helical peptide. Circular dichroism showed 100% helical nature of the peptide in 10 mM SDS. Notably, the peptide exerted significant antimicrobial activity against the reference and antibiotic-resistant clinical isolates belonging to Pseudomonas sp. at a MIC and MBC of 2 and 8 μM, respectively. The progressive disruption and disturbance of cell membrane in the overall topography was observed in the scanning electron microscopy (SEM) micrographs of Pseudomonas aeruginosa ATCC 27853 treated with the peptide as compared to untreated control. The results of time-kill kinetics showed complete lysis at 3x MIC after 50 min of incubation of the microbe with the peptide. Moreover, the peptide did not lyse human RBCs even at the highest concentration of the peptide (10 mM) and retained its activity upon treatment at 0.5 mg/ml trypsin. Cancer cell lines, viz. A549 and MCF-7 were also found to be sensitive to peptide activity showing 50% reduction in survivability at 4 and 2 μM, respectively; however, L929 cells were unaffected. Drastic membrane permeability and necrotic mode of lysis of peptide-treated-A549 cells were affirmed by propidium iodide and live/dead cell staining. The results showed that the designed peptide could be an efficient drug molecule for clinical studies subjected to successful experiments on animal models.

Dimerization of Antimicrobial Peptides: A Promising Strategy to Enhance Antimicrobial Peptide Activity

Antimicrobial resistance is a global health problem with strong social and economic impacts. The development of new antimicrobial agents is considered an urgent challenge. In this regard, Antimicrobial Peptides (AMPs) appear to be novel candidates to overcome this problem. The mechanism of action of AMPs involves intracellular targets and membrane disruption. Although the exact mechanism of action of AMPs remains controversial, most AMPs act through membrane disruption of the target cell. Several strategies have been used to improve AMP activity, such as peptide dimerization. In this review, we focus on AMP dimerization, showing many examples of dimerized peptides and their effects on biological activity. Although more studies are necessary to elucidate the relationship between peptide properties and the dimerization effect on antimicrobial activity, dimerization constitutes a promising strategy to improve the effectiveness of AMPs.

Biological characterization of omw1 and omw2: antimicrobial peptides derived from omwaprin

Two cationic antimicrobial peptides (AMP) were designed based on the snake venom peptide, omwaprin, hypothesized to be shorter, cost effective and potent. Omw1 and omw2 demonstrated significant broad-spectrum antimicrobial activity against standard and clinical strains at a MIC ranging from 15.625 to 250 µg/ml for omw1 and from 31.3 to 500 µg/ml for omw2. Time-kill kinetics revealed that omw1 caused complete lysis of E. coli ATCC 25922 at 1× MIC and S. aureus ATCC 25923 at 2× MIC after 40 and 60 min of incubation, respectively. Membranolytic activity of the peptides was assessed by propidium iodide stain, where red fluorescence was observed in cells treated with the peptides compared to untreated cells. Notable morphological changes were observed in the microbes treated with peptides, as revealed by scanning electron micrographs. Omw1 and omw2 were also potent to inhibit the formation as well as dispersal of matured biofilms at 1/2× MIC against clinical strain, C. albicans. Further, minimal hemolytic activity demonstrated by both the peptides at microbicidal concentration against human erythrocytes proves that the designed peptides were less toxic and potent antimicrobial agents which could be considered for further studies with animal models to affirm its efficiency.

Histidine-rich Modification of a Scorpion-derived Peptide Improves Bioavailability and Inhibitory Activity against HSV-1

Rationale: HSV is one of the most widespread human viral pathogens. HSV-1 infects a large portion of the human population and causes severe diseases. The current clinical treatment for HSV-1 is based on nucleoside analogues, the use of which is limited due to drug resistance, side effects and poor bioavailability. AMPs have been identified as potential antiviral agents that may overcome these limitations. Therefore, we screened anti-HSV-1 peptides from a scorpion-derived AMP library and engineered one candidate into a histidine-rich peptide with significantly improved antiviral activity and development potential.

Methods: A venomous gland cDNA library was constructed from the scorpion Euscorpiops validus in the Yunnan Province of China. Six putative AMPs were characterized from this cDNA library, and the synthesized peptides were screened via plaque-forming assays to determine their virucidal potential. Time of addition experiments according to the infection progress of HSV-1 were used to identify the modes of action for peptides of interest. The histidine-rich modification was designed based on structural analysis of peptides by a helical wheel model and CD spectroscopy. Peptide cellular uptake and distribution were measured by flow cytometry and confocal microscopy, respectively.

Results: The peptide Eval418 was found to have high clearance activity in an HSV-1 plaque reduction assay. Eval418 exhibited dose-dependent and time-dependent inactivation of HSV-1 and dose-dependent inhibition of HSV-1 attachment to host cells. However, Eval418 scarcely suppressed an established HSV-1 infection due to poor cellular uptake. We further designed and modified Eval418 into four histidine-rich derivative peptides with enhanced antiviral activities and lower cytotoxicities. All of the derivative peptides suppressed established HSV-1 infections. One of these peptides, Eval418-FH5, not only had strong viral inactivation activity and enhanced attachment inhibitory activity but also had high inhibitory activity against intracellular HSV-1, which was consistent with its improved intracellular uptake and distribution as confirmed by confocal microscopy and flow cytometry.

Conclusion: We successfully identified an anti-HSV-1 peptide, Eval418, from a scorpion venom peptide library and designed a histidine-rich Eval418 derivative with significantly improved potential for further development as an anti-HSV-1 drug. This successful modification can provide a design strategy to improve the bioavailability, cellular distribution and antiviral activity of peptide agents.

Inhibitory activity and mechanism of two scorpion venom peptides against herpes simplex virus type 1

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Hp1036 and Hp1239 are two new cationic host defense peptides from scorpion venom.

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They inhibitory effect on multiple steps of HSV-1 life cycle.

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They adopted α-helix structure in approximate membrane environment.

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They are virucidal of HSV-1 and destroyed the morphology of HSV-1.

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They easily entered Vero cells and reduced the intracellular viral infectivity.

Herpes simplex virus type 1 (HSV-1) is a widespread human pathogen that causes severe diseases, but there are not effective and safe drugs in clinical therapy besides acyclovir (ACV) and related nucleoside analogs. In this study, two new venom peptides from the scorpion Heterometrus petersii were identified with effective inhibitory effect on HSV-1 infection in vitro. Both Hp1036 and Hp1239 peptides exhibited potent virucidal activities against HSV-1 (EC₅₀ = 0.43 ± 0.09 and 0.41 ± 0.06 μM, respectively) and effective inhibitory effects when added at the viral attachment (EC₅₀ = 2.87 ± 0.16 and 5.73 ± 0.61 μM, respectively), entry (EC₅₀ = 4.29 ± 0.35 and 4.32 ± 0.47 μM, respectively) and postentry (EC₅₀ = 7.86 ± 0.80 and 8.41 ± 0.73 μM, respectively) steps. Both Hp1036 and Hp1239 peptides adopted α-helix structure in approximate membrane environment and resulted in the destruction of the viral morphology. Moreover, Hp1036 and Hp1239 peptides entered Vero cells and reduced the intracellular viral infectivity. Taken together, Hp1036 and Hp1239 peptides are two anti-viral peptides with effective inhibitory effect on multiple steps of HSV-1 life cycle and therefore are good candidate for development as virucides.

Current scenario of peptide-based drugs: the key roles of cationic antitumor and antiviral peptides

Cationic antimicrobial peptides (AMPs) and host defense peptides (HDPs) show vast potential as peptide-based drugs. Great effort has been made in order to exploit their mechanisms of action, aiming to identify their targets as well as to enhance their activity and bioavailability. In this review, we will focus on both naturally occurring and designed antiviral and antitumor cationic peptides, including those here called promiscuous, in which multiple targets are associated with a single peptide structure. Emphasis will be given to their biochemical features, selectivity against extra targets, and molecular mechanisms. Peptides which possess antitumor activity against different cancer cell lines will be discussed, as well as peptides which inhibit virus replication, focusing on their applications for human health, animal health and agriculture, and their potential as new therapeutic drugs. Moreover, the current scenario for production and the use of nanotechnology as delivery tool for both classes of cationic peptides, as well as the perspectives on improving them is considered.

A cancer specific cell-penetrating peptide, BR2, for the efficient delivery of an scFv into cancer cells

Cell-penetrating peptides (CPPs) have proven very effective as intracellular delivery vehicles for various therapeutics. However, there are some concerns about non-specific penetration and cytotoxicity of CPPs for effective cancer treatments. Herein, based on the cell-penetrating motif of an anticancer peptide, buforin IIb, we designed several CPP derivatives with cancer cell specificity. Among the derivatives, a 17-amino acid peptide (BR2) was found to have cancer-specificity without toxicity to normal cells. After specifically targeting cancer cells through interaction with gangliosides, BR2 entered cells via lipid-mediated macropinocytosis. Moreover, BR2 showed higher membrane translocation efficiency than the well-known CPP Tat (49-57). The capability of BR2 as a cancer-specific drug carrier was demonstrated by fusion of BR2 to a single-chain variable fragment (scFv) directed toward a mutated K-ras (G12V). BR2-fused scFv induced a higher degree of apoptosis than Tat-fused scFv in K-ras mutated HCT116 cells. These results suggest that the novel cell-penetrating peptide BR2 has great potential as a useful drug delivery carrier with cancer cell specificity.

ClassAMP: a prediction tool for classification of antimicrobial peptides

Antimicrobial peptides (AMPs) are gaining popularity as anti-infective agents. Information on sequence features that contribute to target specificity of AMPs will aid in accelerating drug discovery programs involving them. In this study, an algorithm called ClassAMP using Random Forests (RFs) and Support Vector Machines (SVMs) has been developed to predict the propensity of a protein sequence to have antibacterial, antifungal, or antiviral activity. ClassAMP is available at http://www.bicnirrh.res.in/classamp/.

Aurein 2.3 functionality is supported by oblique orientated α-helical formation

In this study, an amphibian antimicrobial peptide, aurein 2.3, was predicted to use oblique orientated α-helix formation in its mechanism of membrane destabilisation. Molecular dynamic (MD) simulations and circular dichroism (CD) experimental data suggested that aurein 2.3 exists in solution as unstructured monomers and folds to form predominantly α-helical structures in the presence of a dimyristoylphosphatidylcholine membrane. MD showed that the peptide was highly surface active, which supported monolayer data where the peptide induced surface pressure changes>34 mNm(-1). In the presence of a lipid membrane MD simulations suggested that under hydrophobic mismatch the peptide is seen to insert via oblique orientation with a phenylalanine residue (PHE3) playing a key role in the membrane interaction. There is evidence of snorkelling leucine residues leading to further membrane disruption and supporting the high level of lysis observed using calcein release assays (76%). Simulations performed at higher peptide/lipid ratio show peptide cooperativity is key to increased efficiency leading to pore-formation.

Mechanism of action and specificity of antimicrobial peptides designed based on buforin IIb

Buforin IIb-a synthetic analog of buforin II that contains a proline hinge between the two α-helices and a model α-helical sequence at the C-terminus (3× RLLR)-is a potent cell-penetrating antimicrobial peptide. To develop novel antimicrobial peptides with enhanced activities and specificity/therapeutic index, we designed several analogs (Buf III analogs) by substitutions of amino acids in the proline hinge region and two α-helices of buforin IIb, and examined their antimicrobial activity and mechanism of action. The substitution of hydrophobic residues ([F(6)] and [V(8)]) in the proline hinge region with other hydrophobic residues ([W(6)] and [I(8)]) did not affect antimicrobial activity, while the substitution of the first four amino acids RAGL with a model α-helical sequence increased the antimicrobial activity up to 2-fold. Like buforin IIb, Buf III analogs penetrated the bacterial cell membranes without significantly permeabilizing them and were accumulated inside Escherichia coli. Buf III analogs were shown to bind DNA in vitro and the DNA binding affinity of the peptides correlated linearly with their antimicrobial potency. Among the Buf III analogs, the therapeutic index of Buf IIIb and IIIc (RVVRQWPIG[RVVR](3) and KLLKQWPIG[KLLK](3), respectively) were improved 7-fold compared to that of buforin IIb. These results indicate that Buf III analogs appear to be promising candidates for future development as novel antimicrobial agents.

Rational design of peptides with anti-HCV/HIV activities and enhanced specificity

Lack of vaccines for HCV and HIV makes the antiviral drug development urgently needed. The recently identified HCV NS5A-derived virucidal peptide (C5A) demonstrated a wide spectrum of activities against viruses. In this study, the C5A sequence SWLRDIWDWICEVLSDFK was utilized as the framework to study the effect of the modulation of peptide helicity and hydrophobicity on its anti-HCV and anti-HIV activities. Peptide helicity and hydrophobicity were altered by substitutions of varying amino acids on the non-polar face of C5A. Peptide hydrophobicity has been proved to play a crucial role in peptide anti-HCV or anti-HIV activities. Peptide helicity was relatively independent with antiviral activity. However, peptide analogs with dimerized structure in an aqueous medium while maintaining the ability to be induced into a more helical structure in a hydrophobic environment may tend to show comparable or improved antiviral activity and specificity to C5A. By modulating peptide helicity and hydrophobicity, we improved the specificity of C5A against HCV and HIV by 23- and 69-fold, respectively, in terms of the ratio of hemolytic activity to antiviral activity. We demonstrated that obtained by de novo design approach, peptide I6L/I10L/V13L may be a promising candidate as a new anti-HCV and anti-HIV therapeutic.

iTRAQ-coupled 2-D LC-MS/MS analysis of membrane protein profile in Escherichia coli incubated with apidaecin IB

Apidaecins are a series of proline-rich, 18- to 20-residue antimicrobial peptides produced by insects. They are predominantly active against the gram-negative bacteria. Previous studies mainly focused on the identification of their internal macromolecular targets, few addressed on the action of apidaecins on the molecules, especially proteins, of bacterial cell membrane. In this study, iTRAQ-coupled 2-D LC-MS/MS technique was utilized to identify altered membrane proteins of Escherichia coli cells incubated with one isoform of apidaecins--apidaecin IB. Cell division protease ftsH, an essential regulator in maintenance of membrane lipid homeostasis, was found to be overproduced in cells incubated with apidaecin IB. Its over-expression intensified the degradation of cytoplasmic protein UDP-3-O-acyl-N- acetylglucosamine deacetylase, which catalyzes the first committed step in the biosynthesis of the lipid A moiety of LPS, and thus leaded to the further unbalanced biosynthesis of LPS and phospholipids. Our findings suggested a new antibacterial mechanism of apidaecins and perhaps, by extension, for other proline-rich antimicrobial peptides.

Enhancement of the cancer targeting specificity of buforin IIb by fusion with an anionic peptide via a matrix metalloproteinases-cleavable linker

Buforin IIb is a novel cell-penetrating anticancer peptide derived from histone H2A. In this study, we enhanced the cancer targeting specificity of buforin IIb using a tumor-associated enzyme-controlled activation strategy. Buforin IIb was fused with an anionic peptide (modified magainin intervening sequence, MMIS), which neutralizes the positive charge of buforin IIb and thus renders it inactive, via a matrix metalloproteinases (MMPs)-cleavable linker. The resulting MMIS:buforin IIb fusion peptide was completely inactive against MMPs-nonproducing cells. However, when the fusion peptide was administrated to MMPs-producing cancer cells, it regained the killing activity by releasing free buforin IIb through MMPs-mediated cleavage. Moreover, the activity of the fusion peptide toward MMPs-producing cancer cells was significantly decreased when the cells were pretreated with a MMP inhibitor. Taken together, these data indicate that the cancer targeting specificity of MMIS:buforin IIb is enhanced compared to the parent peptide by reactivation at the specialized areas where MMPs are pathologically produced.

Antimicrobial peptides from amphibians

Increased prevalence of multi-drug resistance in pathogens has encouraged researchers to focus on finding novel forms of anti-infective agents. Antimicrobial peptides (AMPs) found in animal secretions are components of host innate immune response and have survived eons of pathogen evolution. Thus, they are likely to be active against pathogens and even those that are resistant to conventional drugs. Many peptides have been isolated and shown to be effective against multi-drug resistant pathogens. More than 500 AMPs have been identified from amphibians. The abundance of AMPs in frog skin is remarkable and constitutes a rich source for design of novel pharmaceutical molecules. Expression and post-translational modifications, discovery, activities and probable therapeutic application prospects of amphibian AMPs will be discussed in this article.

Peptide inhibitors against influenza virus

Influenza A virus is a particularly problematic virus because of its ability to cause high levels of morbidity on a global scale within a remarkably short period of time. It also has the potential to kill very large numbers of people as occurred in the Spanish influenza pandemic in 1918. Options for antiviral therapy are limited because of the paucity of available drugs and the rapid mutation rate of the virus leading to the emergence of drug-resistant strains. The current H1N1 pandemic and potential threats posed by other strains highlight the need to develop novel therapeutic and prophylactic strategies. Here, we summarize the current state and recent developments of peptide-based inhibitors of influenza A virus.

Therapeutic approaches using host defence peptides to tackle herpes virus infections

One of the most common viral infections in humans is caused by herpes simplex virus (HSV). It can easily be treated with nucleoside analogues (e.g., acyclovir), but resistant strains are on the rise. Naturally occurring antimicrobial peptides have been demonstrated to possess antiviral activity against HSV. New evidence has also indicated that these host defence peptides are able to selectively stimulate the innate immune system to fight of infections. This review will focus on the anti-HSV activity of such peptides (both natural and synthetic), describe their mode of action and their clinical potential.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

A cumulative experience examining the effect of natural and synthetic antimicrobial peptides vs. Chlamydia trachomatis

We tested the activity of 48 structurally diverse antimicrobial peptides against Chlamydia trachomatis, serovar L2. The peptides' activity against C. trachomatis, serovar L2 was measured in 48-h McCoy cell shell vial assays. Peptides of 16-20 amino acids were more active than larger peptides, such as defensins. Beta-sheet protegrins, as well as alpha-helical peptides such as novispirin (G-10) were equally active. Enantiomers were as active as native structures. Moderate-sized circular mini-defensins were less effective against C. trachomatis. Moderate-sized cationic peptides may be useful in microbicide preparations designed to prevent chlamydial infection.

Modelling of anti-HSV activity of lactoferricin analogues using amino acid descriptors

Herpes simplex virus (HSV) causes a number of diseases and new therapies are being pursued vigorously. Earlier studies have shown that modified peptides based on lactoferricins reduce HSV-1 and HSV-2 infection, and structure-activity studies indicate that the anti-viral activity correlates with the binding affinity for heparan sulphate and chondroitin sulphate. In this study it is shown that theoretically derived amino acid descriptors can be used to model the anti-viral activity of peptides, as well as other peptide properties, even more accurately.

Detergent-like properties of magainin antibiotic peptides: a 31P solid-state NMR spectroscopy study

(31)P solid-state NMR spectroscopy has been used to investigate the macroscopic phase behavior of phospholipid bilayers in the presence of increasing amounts of magainin antibiotic peptides. Addition of >1 mol% magainin 2 to gel-phase DMPC or liquid crystalline POPC membranes respectively, results in (31)P NMR spectra that are characterized by the coexistence of isotropic signals and line shapes typical for phospholipid bilayers. The isotropic signal intensity is a function of temperature and peptide concentration. At peptide concentrations >4 mol% of the resulting phospholipid (31)P NMR spectra are characteristic of magnetically oriented POPC bilayers suggesting the formation of small disk-like micelles or perforated sheets. In contrast, addition of magainin to acidic phospholipids results in homogenous bilayer-type (31)P NMR spectra with reduced chemical shift anisotropies. The results presented are in good agreement with the interfacial insertion of magainin helices with an alignment parallel to the surface of the phospholipid bilayers. The resulting curvature strain results in detergent-like properties of the amphipathic helical peptides.

Phylloseptins: a novel class of anti-bacterial and anti-protozoan peptides from the Phyllomedusa genus

Six novel peptides called phylloseptins (PS-1, -2, -3, -4, -5, and -6) showing anti-bacterial (PS-1) and anti-protozoan (PS-4 and -5) activities were isolated from the skin secretion of the Brazilian tree-frogs, Phyllomedusa hypochondrialis and Phyllomedusa oreades. Phylloseptins have a primary structure consisting of 19-21 amino acid residues (1.7-2.1 kDa). They have common structural features, such as a highly conserved N-terminal region and C-terminal amidation. Phylloseptin-1 (FLSLIPHAINAVSAIAKHN-NH2) demonstrated a strong effect against gram-positive and gram-negative bacteria (MICs ranging from 3 to 7.9 microM), without showing significant hemolytic activity (<0.6% at the MIC range) towards mammalian cells. Atomic force microscopy experiments indicated that the bacteriolytic properties of these peptides might be related to their disruptive action on the cell membrane, characterized by a number of bubble-like formations, preceding every cell lysis. PS-4 and PS-5 showed anti-protozoan activity with IC50 at about 5 microM for Trypanosoma cruzi.

Antiviral activity of antimicrobial cationic peptides against Junin virus and herpes simplex virus

The in vitro antiviral activity of antimicrobial cationic peptides: cecropin A, melittin, magainin I and II and indolicidin against the arenavirus Junin virus (JV), and herpes simplex virus type 1 (HSV-1) and 2 (HSV-2) was evaluated. Cecropin A effectively inhibited JV multiplication and failed to affect HSV replication whereas melittin impeded the multiplication of JV and HSV, but was highly toxic for the host cell. Magainins I and II exhibited inhibitory action toward HSV-1 and HSV-2 but were inactive against JV. Only indolicidin showed a direct inactivation effect on cell-free virus stocks. Besides its inhibitory effect on JV replication cecropin A also was active against the arenaviruses Tacaribe and Pichinde, mainly affecting late events of arenavirus multiplication cycle by preventing viral morphogenesis and egress from infected cells.

The antiviral activity of naturally occurring proteins and their peptide fragments after chemical modification

Chemical modification of the proteins bovine serum albumin, alpha-lactalbumin, beta-lactoglobulin and chicken lysozyme by 3-hydroxyphthalic anhydride (3-HP) yielded compounds which exerted antiviral activity in vitro as compared with the native unmodified proteins. Of the three enveloped viruses tested, human herpes simplex virus type 1 (HSV-1), bovine parainfluenza virus type 3 and porcine respiratory corona virus, only HSV-1 proved sensitive to the 3-HP-proteins. All of the chemically modified proteins presented antiviral activity against HSV-1 when assayed before, during or after infection. However, to achieve HSV-1 inhibition, significantly higher concentrations of the modified proteins were required if present before infection as compared to during or after infection. Our results suggest that multiple mechanisms are involved in the inhibition of HSV-1 infection. Proteolytical digestion of albumin, alpha-lactalbumin, beta-lactoglobulin and lysozyme by trypsin, chymotrypsin and pepsin yielded several peptide fragments with antiherpetic activity. Chemical modification of these peptide fragments by 3-HP generated peptides with antiviral activity, however, this was almost always combined with a cytotoxic effect on the Vero cells. Overall, our results suggest that targeted chemical modification of some natural products might provide compounds effective against HSV-1 infection.

Lactoferrin and lactoferricin inhibit Herpes simplex 1 and 2 infection and exhibit synergy when combined with acyclovir

Lactoferrin (LF) is a multifunctional glycoprotein, which plays an important role in immune regulation and defense mechanisms against bacteria, fungi, and viruses. Upon peptic digestion of LF, a peptide called lactoferricin (Lfcin) is generated. Lfcin corresponds to the N-terminal part of the protein. In this study we investigated the antiviral activity of bovine and human Lfcin against Herpes simplex virus (HSV)-1 and HSV-2. The 50% effective concentrations (EC(50)) for LF and Lfcin against several clinical isolates of HSV-1 and HSV-2, including acyclovir (ACV)-resistant strains, were determined. We further evaluated the effect of the combination of either LF or Lfcin with ACV against HSV-1 and HSV-2. Synergy was observed between both LF or Lfcin in combination with ACV against the HSV laboratory strains. The 50% effective concentration (EC(50)) for ACV and LF or Lfcin, when combined with ACV, could be reduced by two- to sevenfold compared to the EC(50) when the drugs were used alone.

Nonmammalian vertebrate antibiotic peptides

With the exception of cyclostomes, all vertebrates share the common immune strategy of adaptive, highly specific immunity, based on the products of recombination-activating genes and recombined noninherited receptors for antigens. In addition, they have retained ancient vectors of innate immunity, such as antimicrobial peptides, which are widespread in all eukaryotic organisms and show a high degree of structural homology across most animal taxa. Recently, these substances have become the objects of intensive study for their outstanding bioactive properties with the aim to be applied as very efficient antibiotics, antimicrobials, and even cancerostatics in clinical practice.

Dermaseptins from Phyllomedusa oreades and Phyllomedusa distincta. Anti-Trypanosoma cruzi activity without cytotoxicity to mammalian cells

Amphibian skin secretions are known as a rich source of biologically active molecules, most of which are alkaloids, biogenic amines, and peptides. Dermaseptins are a class of antimicrobial peptides present in tree frogs of the Phyllomedusa genus. They are cationic molecules of 28-34 residues that permeabilize the membrane of Gram-positive and Gram-negative bacteria, yeasts, and filamentous fungi, showing little or no hemolytic activity. This work reports the isolation, molecular mass analysis, primary structure determination, biological activities, and potential therapeutic applications of an antimicrobial peptide found in the skin secretion of Phyllomedusa oreades, which is a newly described amphibian species endemic of the Brazilian savanna. DS 01 is a 29-residue-long peptide with a molecular mass of 2793.39 Da showing antibacterial properties against Gram-positive and Gram-negative bacteria in the range of 3-25 microm. Anti-protozoan activity was investigated using T. cruzi in its trypomatigote and epimastigote forms cultivated in both cell culture and blood media. Within 2 h after incubation with DS 01 at a final concentration of approximately 6 microm, no protozoan cells were detected. Two synthetic dermaseptins, described previously by our group and named dermadistinctins K and L (DD K and DD L), also had their anti-Trypanosoma cruzi activity investigated and demonstrated similar properties. Toxicity of DS 01 to mouse erythrocytes and white blood cells was evaluated by means of atomic force microscopy and flow cytometry. No morphological alterations were observed at a lytic concentration of DS 01, suggesting its therapeutic value especially as an anti-T. cruzi agent to prevent infections during blood transfusion.

In vitro antiviral activity of dermaseptins against herpes simplex virus type 1

The in vitro antiviral activity of dermaseptins (S1-S5) against herpes simplex virus type 1 (HSV1) was investigated. These peptides were incubated with the virus and its target cells under various conditions, and their effects were examined by the cytopathic effect inhibition assay or by reduction in virus yield in Hep-2 cell cultures as well as by direct immunofluorescence. Dermaseptin S4 displayed the strongest antiviral effect against HSV1, at micromolar doses. Experiments including acyclovir as a reference antiviral agent were performed to investigate the mode of action of this dermaseptin. In contrast to acyclovir, dermaseptin S4 showed its inhibitory effect only when applied to the virus before, or during virus adsorption to the target cells. This suggested that the activity of this dermaseptin was exerted at a very early stage of the viral multiplication cycle, most likely at the virus-cell interface.

Animal antimicrobial peptides: an overview

Antibiotic peptides are a key component of the innate immune systems of most multicellular organisms. Despite broad divergences in sequence and taxonomy, most antibiotic peptides share a common mechanism of action, i.e., membrane permeabilization of the pathogen. This review provides a general introduction to the subject, with emphasis on aspects such as structural types, post-translational modifications, mode of action or mechanisms of resistance. Some of these questions are treated in depth in other reviews in this issue. The review also discusses the role of antimicrobial peptides in nature, including several pathological conditions, as well as recent accounts of their application at the preclinical level.

Structural and functional implications of a proline residue in the antimicrobial peptide gaegurin

Although it is commonly known as a helix breaker, proline residues have been found in the alpha-helical regions of many peptides and proteins. The antimicrobial peptide gaegurin displays alpha-helical structure and has a central proline residue (P14). The structure and activity of gaegurin and its alanine derivative (P14A) were determined by various spectroscopic methods, restrained molecular dynamics, and biological assays. Both P14 and P14A exhibited cooperative helix formation in solution, but the helical stability of P14 was reduced substantially when compared to that of P14A. Chemical-shift analysis indicated that both of the peptides formed curved helices and that P14 showed diminished stability in the region around the central proline. However, hydrogen-exchange data revealed remarkable differences in the location of stable amide protons. P14 showed a stable region in the concave side of the curved helix, while P14A exhibited a stable region in the central turn of the helix. The model structure of P14 exhibited a pronounced kink, in contrast to the uniform helix of P14A. Both peptides showed comparable binding affinities for negatively charged lipids, while P14 had a considerably reduced affinity for a neutral lipid. With its destabilized alpha-helix, P14 exhibited greater antibacterial activity than did P14A. Hence, electrostatic interaction between helical peptides and lipid membranes is believed to be the dominant factor for antibacterial activity. Moreover, helical stability can modulate peptide binding to membranes that is driven by electrostatic interactions. The observation that P14 is a more potent antibacterial agent than P14A implies that the helical kink of P14 plays an important role in the disruption of bacterial membranes.

Characterization of novel antimicrobial peptoids

Peptoids differ from peptides in that peptoids are composed of N-substituted rather than alpha-carbon-substituted glycine units. In this paper we report the in vitro and in vivo antibacterial activities of several antibacterial peptoids discovered by screening combinatorial chemistry libraries for bacterial growth inhibition. In vitro, the peptoid CHIR29498 and some of its analogues were active in the range of 3 to 12 microg/ml against a panel of gram-positive and gram-negative bacteria which included isolates which were resistant to known antibiotics. Peptoid antimicrobial activity against Staphylococcus aureus was rapid, bactericidal, and independent of protein synthesis. beta-Galactosidase and propidium iodide leakage assays indicated that the membrane is the most likely target of activity. Positional isomers of an active peptoid were also active, consistent with a mode of action, such as membrane disruption, that does not require a specific fit between the molecule and its target. In vivo, CHIR29498 protected S. aureus-infected mice in a simple infection model.

Antimicrobial peptides derived from pepsinogens in the stomach of the bullfrog, Rana catesbeiana

Three antimicrobial peptides, which had strong antimicrobial activity against a broad spectrum of microorganisms, were isolated from the stomach of the bullfrog, Rana catesbeiana. Two of the antimicrobial peptides were found to be derived from the N-terminal sequences of pepsinogen A and C prosequences. The amino acid sequences of the new antimicrobial peptides, named bullfrog pepsinogen A-derived antimicrobial peptide (bPaAP) and bullfrog pepsinogen C-derived antimicrobial peptide (bPcAP), were Gly-Val-Val-Lys-Val-Ser-Arg-Leu-Lys-Gly-Glu-Ser-Leu-Arg-Ala-Arg-Leu (MW 1865.5) and Ile-Ile-Lys-Val-Pro-Leu-Lys-Lys-Phe-Lys-Ser-Met-Arg-Glu-Val-Met-Arg-A sp-His-Gly-Ile-Lys-Ala-Pro-Val-Val-Asp-Pro-Ala-Thr-Lys-Tyr (MW 3691.6), respectively. The bPaAP and bPcAP adopted 35% and 42% amphipathic alpha-helical structure in 50% trifluoroethanol, respectively, and were non-hemolytic up to a concentration of 200 microg/ml. Synthesized pepsinogen C prosequences of monkey and human, which had similar structural characteristics as bPaAP and bPcAP, also showed antimicrobial activity at concentrations of 10-200 microg/ml. The third peptide was buforin I, previously found in the stomach of the Asian toad, Bufo bufo gargarizans. These findings strongly suggest that peptides derived from the prosequences of pepsinogens, along with buforin I, may contribute to the antimicrobial function of the gastrointestinal mucosa of vertebrates, including human.

Structure and dynamics of the antibiotic peptide PGLa in membranes by solution and solid-state nuclear magnetic resonance spectroscopy

PGLa, a 21-residue member of the magainin family of antibiotic peptides, is shown to be helical between residues 6 and 21 when associated with detergent micelles by multidimensional solution nuclear magnetic resonance (NMR) spectroscopy. Solid-state NMR experiments on specifically 15N-labeled peptides in oriented phospholipid bilayer samples show that the helix axis is parallel to the plane of the bilayers. 15N solid-state NMR powder pattern line shapes obtained on unoriented samples demonstrate that the amino-terminal residues are highly mobile and that the fluctuations of backbone sites decrease from Ala6 toward the carboxy terminus. The powder pattern observed for 15N-labeled Ala20 is essentially that expected for a rigid site. These findings are similar to those for the 23-residue magainin2 peptide in membrane environments.

A novel antimicrobial peptide from the loach, Misgurnus anguillicaudatus

A novel antimicrobial peptide, named misgurin, was isolated and characterized from the loach (mudfish), Misgurnus anguillicaudatus. The 21-amino-acid peptide with a molecular mass of 2502 Da was purified to homogeneity using a heparin-affinity column and C18 reverse-phase and gel-permeation high-performance liquid chromatography. The complete amino acid sequence of misgurin, which was determined by an automated amino acid sequencer, was Arg-Gln-Arg-Val-Glu-Glu-Leu-Ser-Lys-Phe-Ser-Lys-Lys-Gly-Ala-Ala-Ala-Arg- Arg-Arg-Lys. Misgurin is a strongly basic peptide which has 5 arginine and 4 lysine residues. Comparison of the amino acid sequence with those of other known antimicrobial peptides revealed that misgurin was a novel antimicrobial peptide. Misgurin showed a strong antimicrobial activity in vitro against a broad spectrum of microorganisms without significant hemolytic activity and was about 6 times more potent than magainin 2. Scanning electron microscopy confirmed that the peptide caused damage to the cell membrane by a pore-forming mechanism similar to that of magainin 2. This damage occurred at the minimal inhibition concentration (MIC), but at higher concentration than MIC it lysed the cell.

Inhibition of a plant virus infection by analogs of melittin

An approach that enables identification of specific synthetic peptide inhibitors of plant viral infection is reported. Synthetic analogs of melittin that have sequence and structural similarities to an essential domain of tobacco mosaic virus coat protein were found to possess highly specific antiviral activity. This approach involves modification of residues located at positions analogous to those that are critical for virus assembly. The degree of inhibition found correlates well with sequence similarities between the viral capsid protein and the melittin analogs studied as well as with the induced conformational changes that result upon interaction of the peptides and ribonucleic acid.