A new temporin with antibacterial activity and cytotoxicity from the skin secretion of Lithobates palmipes (Spix, 1824) (Amphibia: Ranidae) from Brazilian Atlantic Forest

This work investigated the peptide profile of skin secretion from Lithobates palmipes collected from the Brazilian Atlantic Forest. The secretion was submitted to reversed phase high-performance liquid chromatography (RP-HPLC) and the fractions were screened for antibacterial activity. RP-HPLC resulted in the separation of several peaks, among which 10 showed antibacterial activity and contained peptides of the ranatuerin, brevinin and temporin families. Fraction 6 was resubmitted to RP-HPLC and a novel peptide from temporin family (temporin-PMb) had its primary structure determined. Temporin-PMb and non-amidated temporin-PMb were synthesized, purified, and evaluated for antibacterial activity, hemolytic activity and cytotoxicity to keratinocytes and cancer cells. Temporin-PMb was active against Klebsiella pneumoniae, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa as well as against methicilin-resistant S. aureus (MRSA) and Acinetobacter baumannii. It was cytotoxic to human cervical adenocarcinoma cells (HeLa) and human mammary adenocarcinoma cells (MCF7) with IC50 of 32.4 and 24.1 μM, respectively. It was also toxic to human keratinocytes (HaCaT; IC50 of 25.0 μM) and showed hemolytic activity. The non-amidated form showed low hemolytic activity and lower HaCaT toxicity, but was only effective against E. coli, S. aureus MRSA, and A. baumanii. In conclusion, Atlantic Forest L. palmipes skin secretion contained different bioactive peptides, including a novel temporin with antibacterial effect and cytotoxicity towards human cancer cells. The amide group was responsible for the activities of the wild-type temporin-PMb. Peptide engineering studies are encouraged aiming at minimizing unwanted effects.

Molecular farming for sustainable production of clinical-grade antimicrobial peptides

Antimicrobial peptides (AMPs) are emerging as next-generation therapeutics due to their broad-spectrum activity against drug-resistant bacterial strains and their ability to eradicate biofilms, modulate immune responses, exert anti-inflammatory effects and improve disease management. They are produced through solid-phase peptide synthesis or in bacterial or yeast cells. Molecular farming, i.e. the production of biologics in plants, offers a low-cost, non-toxic, scalable and simple alternative platform to produce AMPs at a sustainable cost. In this review, we discuss the advantages of molecular farming for producing clinical-grade AMPs, advances in expression and purification systems and the cost advantage for industrial-scale production. We further review how 'green' production is filling the sustainability gap, streamlining patent and regulatory approvals and enabling successful clinical translations that demonstrate the future potential of AMPs produced by molecular farming. Finally, we discuss the regulatory challenges that need to be addressed to fully realize the potential of molecular farming-based AMP production for therapeutics.

Antimicrobial peptides designed by computational analysis of proteomes

Antimicrobial peptides (AMPs) are promising cationic and amphipathic molecules to fight antibiotic resistance. To search for novel AMPs, we applied a computational strategy to identify peptide sequences within the organisms' proteome, including in-house developed software and artificial intelligence tools. After analyzing 150.450 proteins from eight proteomes of bacteria, plants, a protist, and a nematode, nine peptides were selected and modified to increase their antimicrobial potential. The 18 resulting peptides were validated by bioassays with four pathogenic bacterial species, one yeast species, and two cancer cell-lines. Fourteen of the 18 tested peptides were antimicrobial, with minimum inhibitory concentrations (MICs) values under 10 µM against at least three bacterial species; seven were active against Candida albicans with MICs values under 10 µM; six had a therapeutic index above 20; two peptides were active against A549 cells, and eight were active against MCF-7 cells under 30 µM. This study's most active antimicrobial peptides damage the bacterial cell membrane, including grooves, dents, membrane wrinkling, cell destruction, and leakage of cytoplasmic material. The results confirm that the proposed approach, which uses bioinformatic tools and rational modifications, is highly efficient and allows the discovery, with high accuracy, of potent AMPs encrypted in proteins.

A novel bioinformatic method for the identification of antimicrobial peptides in metagenomes

AIMS

This study aimed to develop a new bioinformatic approach for the identification of novel antimicrobial peptides (AMPs), which did not depend on sequence similarity to known AMPs held within databases, but on structural mimicry of another antimicrobial compound, in this case an ultrashort, synthetic, cationic lipopeptide (C12-OOWW-NH2).

METHODS AND RESULTS

When applied to a collection of metagenomic datasets, our outlined bioinformatic method successfully identified several short (8-10aa) functional AMPs, the activity of which was verified via disk diffusion and minimum inhibitory concentration assays against a panel of 12 bacterial strains. Some peptides had activity comparable to, or in some cases, greater than, those from published studies that identified AMPs using more conventional methods. We also explored the effects of modifications, including extension of the peptides, observing an activity peak at 9-12aa. Additionally, the inclusion of a C-terminal amide enhanced activity in most cases. Our most promising candidate (named PB2-10aa-NH2) was thermally stable, lipid-soluble, and possessed synergistic activity with ethanol but not with a conventional antibiotic (streptomycin).

CONCLUSIONS

While several bioinformatic methods exist to predict AMPs, the approach outlined here is much simpler and can be used to quickly scan huge datasets. Searching for peptide sequences bearing structural similarity to other antimicrobial compounds may present a further opportunity to identify novel AMPs with clinical relevance, and provide a meaningful contribution to the pressing global issue of AMR.

Progressive Design of a Ranatuerin-2 Peptide from Amolops wuyiensis: Enhancement of Bioactivity and In Vivo Efficacy

Antimicrobial peptides (AMPs) that exert multiple functions are considered promising candidates to combat the bacterial drug resistance crisis. Nowadays, targeted peptide modification has been widely recognised to improve biological activity and make up for deficiencies in clinical applications such as toxicity. In this study, a helix-loop peptide was isolated and identified from the skin secretion of the Wuyi torrent frog Amolops wuyiensis, namely, ranatuerin-2-AW (R2AW) (GFMDTAKNVAKNVAATLLDKLKCKITGGC). Target modifications were made to R2AW to study the structure-activity relationships and to optimise its bioactivities. Five analogues were progressively designed via residue substitution and truncation and the antibacterial and anticancer activities were evaluated. We found that the serine-substitution and cyclic-domain-deletion products showed similar antibacterial activity to the natural peptide R2AW, implying that the disulphide bridge and Rana box were dispensable for the antibacterial activity of ranatuerin-2 peptides. Notably, the cationicity- and hydrophobicity-enhanced variant, [Lys4,19, Leu20]R2AW(1-22)-NH2, exhibited significantly optimised antibacterial and anticancer activities. Additionally, it killed bacteria by membrane disruption at a highly efficient rate. Moreover, [Lys4,19, Leu20]R2AW(1-22)-NH2 exerted potential in vivo efficacy in a methicillin-resistant Staphylococcus aureus (MRSA)-infected waxworm model. Overall, this study demonstrated some rational design ideas for optimising the dual antibacterial and anticancer activities of ranatuerin-2 peptides and it proposes [Lys4,19, Leu20]R2AW(1-22)-NH2 as an appealing candidate for therapeutic development.

Impact of chemical modifications on the antimicrobial and hemolytic activity of helical amphipathic peptide Lasioglossin LL-III

Insect venom is abundant in potential antimicrobial peptides (AMPs), which can serve as novel alternatives to conventional antibiotics. Among them, Lasioglossin III LL-III) is a promising candidate with a broad spectrum against many fungi strains and both types of bacteria, whereas almost non-toxic to red blood cells. Many chemical approaches have been recently applied to improve its pharmacological properties and provide useful information regarding structure-activity relationships. Hence, this review focused on highlighting the lesson learned from each modification and supporting the future design of potent, selective, and metabolically stable AMPs.

Molecular Modification of Kex2 P1' Site Enhances Expression and Druggability of Fungal Defensin

Pichia pastoris is the widely used expression system for producing recombinant secretory proteins. It is known that Kex2 protease plays a vital role in the process of protein secretion, in which the P1' site affects its cleavage efficiency. To enhance the expression level of fungal defensin-derived peptide NZ2114, this work attempts to optimize the P1' site of Kex2 by replacing it with 20 amino acids in turn. The results showed that when the amino acid of the P1' site was changed to Phe (F), the yield of target peptide significantly increased from 2.39 g/L to 4.81 g/L. Additionally, the novel peptide F-NZ2114 (short for FNZ) showed strong antimicrobial activity against Gram-positive (G⁺) bacteria, especially for Staphylococcus aureus and Streptococcus agalactiae (MIC: 4-8 μg/mL). The FNZ was very stable and retained high activity in various conditions; in addition, a low cytotoxicity and no hemolysis were observed even at a high concentration of 128 μg/mL, and a longer postantibiotic effect was reached. The above results indicate that this engineering strategy provided a feasible optimization scheme for enhancing the expression level and druggability of this antimicrobial peptide from fungal defensin and other similar targets by this updated recombinant yeast.

Genome mining unveils a class of ribosomal peptides with two amino termini

The era of inexpensive genome sequencing and improved bioinformatics tools has reenergized the study of natural products, including the ribosomally synthesized and post-translationally modified peptides (RiPPs). In recent years, RiPP discovery has challenged preconceptions about the scope of post-translational modification chemistry, but genome mining of new RiPP classes remains an unsolved challenge. Here, we report a RiPP class defined by an unusual (S)-N2,N2-dimethyl-1,2-propanediamine (Dmp)-modified C-terminus, which we term the daptides. Nearly 500 daptide biosynthetic gene clusters (BGCs) were identified by analyzing the RiPP Recognition Element (RRE), a common substrate-binding domain found in half of prokaryotic RiPP classes. A representative daptide BGC from Microbacterium paraoxydans DSM 15019 was selected for experimental characterization. Derived from a C-terminal threonine residue, the class-defining Dmp is installed over three steps by an oxidative decarboxylase, aminotransferase, and methyltransferase. Daptides uniquely harbor two positively charged termini, and thus we suspect this modification could aid in membrane targeting, as corroborated by hemolysis assays. Our studies further show that the oxidative decarboxylation step requires a functionally unannotated accessory protein. Fused to the C-terminus of the accessory protein is an RRE domain, which delivers the unmodified substrate peptide to the oxidative decarboxylase. This discovery of a class-defining post-translational modification in RiPPs may serve as a prototype for unveiling additional RiPP classes through genome mining.

Structural and Functional Characterization of the Newly Designed Antimicrobial Peptide Crabrolin21

(1) Background: antimicrobial resistance is becoming a dramatic problem for public health, and the design of new antimicrobial agents is an active research area. (2) Methods: based on our previous work, we designed an improved version of the crabrolin peptide and characterized its functional and structural properties with a wide range of techniques. (3) Results: the newly designed peptide, crabrolin21, is much more active than the previous ones and shows specific selectivity towards bacterial cells. (4) Conclusions: crabrolin21 shows interesting properties and deserves further studies.

Efficient in planta production of amidated antimicrobial peptides that are active against drug-resistant ESKAPE pathogens

Antimicrobial peptides (AMPs) are promising next-generation antibiotics that can be used to combat drug-resistant pathogens. However, the high cost involved in AMP synthesis and their short plasma half-life render their clinical translation a challenge. To address these shortcomings, we report efficient production of bioactive amidated AMPs by transient expression of glycine-extended AMPs in Nicotiana benthamiana line expressing the mammalian enzyme peptidylglycine α-amidating mono-oxygenase (PAM). Cationic AMPs accumulate to substantial levels in PAM transgenic plants compare to nontransgenic N. benthamiana. Moreover, AMPs purified from plants exhibit robust killing activity against six highly virulent and antibiotic resistant ESKAPE pathogens, prevent their biofilm formation, analogous to their synthetic counterparts and synergize with antibiotics. We also perform a base case techno-economic analysis of our platform, demonstrating the potential economic advantages and scalability for industrial use. Taken together, our experimental data and techno-economic analysis demonstrate the potential use of plant chassis for large-scale production of clinical-grade AMPs.

Genome mining unveils a class of ribosomal peptides with two amino termini

The era of inexpensive genome sequencing and improved bioinformatics tools has reenergized the study of natural products, including the ribosomally synthesized and post-translationally modified peptides (RiPPs). In recent years, RiPP discovery has challenged preconceptions about the scope of post-translational modification chemistry, but genome mining of new RiPP classes remains an unsolved challenge. Here, we report a RiPP class defined by an unusual ( S )- N ₂ , N ₂ -dimethyl-1,2-propanediamine (Dmp)-modified C -terminus, which we term the daptides. Nearly 500 daptide biosynthetic gene clusters (BGCs) were identified by analyzing the RiPP Recognition Element (RRE), a common substrate-binding domain found in half of prokaryotic RiPP classes. A representative daptide BGC from Microbacterium paraoxydans DSM 15019 was selected for experimental characterization. Derived from a C -terminal threonine residue, the class-defining Dmp is installed over three steps by an oxidative decarboxylase, aminotransferase, and methyltransferase. Daptides uniquely harbor two positively charged termini, and thus we suspect this modification could aid in membrane targeting, as corroborated by hemolysis assays. Our studies further show that the oxidative decarboxylation step requires a functionally unannotated accessory protein. Fused to the C -terminus of the accessory protein is an RRE domain, which delivers the unmodified substrate peptide to the oxidative decarboxylase. This discovery of a class-defining post-translational modification in RiPPs may serve as a prototype for unveiling additional RiPP classes through genome mining.

Recombinant Expression and Chemical Amidation of Isotopically Labeled Native Melittin

Post-translational modifications are ubiquitous in the eukaryotic proteome. However, these modifications are rarely incorporated in NMR studies of eukaryotic proteins, which are typically produced through recombinant expression in E. coli. Melittin is the primary peptide in honey bee venom. Its native C-terminal amide significantly affects its equilibrium structure and dynamics in solution and is thus a prerequisite for studying its native structure and function. Here, we present a method for producing triply isotopically labeled (2H, 13C, and 15N) native melittin through recombinant expression followed by chemical amidation. We then show that structural models produced with AlphaFold-Multimer are in even better agreement with experimental residual dipolar couplings than the 2.0 Å resolution X-ray crystal structure for residues G3-K23.

Associating Biological Activity and Predicted Structure of Antimicrobial Peptides from Amphibians and Insects

Antimicrobial peptides (AMPs) are a diverse class of short, often cationic biological molecules that present promising opportunities in the development of new therapeutics to combat antimicrobial resistance. Newly developed in silico methods offer the ability to rapidly discover numerous novel AMPs with a variety of physiochemical properties. Herein, using the rAMPage AMP discovery pipeline, we bioinformatically identified 51 AMP candidates from amphibia and insect RNA-seq data and present their in-depth characterization. The studied AMPs demonstrate activity against a panel of bacterial pathogens and have undetected or low toxicity to red blood cells and human cultured cells. Amino acid sequence analysis revealed that 30 of these bioactive peptides belong to either the Brevinin-1, Brevinin-2, Nigrocin-2, or Apidaecin AMP families. Prediction of three-dimensional structures using ColabFold indicated an association between peptides predicted to adopt a helical structure and broad-spectrum antibacterial activity against the Gram-negative and Gram-positive species tested in our panel. These findings highlight the utility of associating the diverse sequences of novel AMPs with their estimated peptide structures in categorizing AMPs and predicting their antimicrobial activity.

Membranolytic Mechanism of Amphiphilic Antimicrobial β-Stranded [KL]n Peptides

Amphipathic peptides can act as antibiotics due to membrane permeabilization. KL peptides with the repetitive sequence [Lys-Leu]_n-NH₂ form amphipathic β-strands in the presence of lipid bilayers. As they are known to kill bacteria in a peculiar length-dependent manner, we suggest here several different functional models, all of which seem plausible, including a carpet mechanism, a β-barrel pore, a toroidal wormhole, and a β-helix. To resolve their genuine mechanism, the activity of KL peptides with lengths from 6–26 amino acids (plus some inverted LK analogues) was systematically tested against bacteria and erythrocytes. Vesicle leakage assays served to correlate bilayer thickness and peptide length and to examine the role of membrane curvature and putative pore diameter. KL peptides with 10–12 amino acids showed the best therapeutic potential, i.e., high antimicrobial activity and low hemolytic side effects. Mechanistically, this particular window of an optimum β-strand length around 4 nm (11 amino acids × 3.7 Å) would match the typical thickness of a lipid bilayer, implying the formation of a transmembrane pore. Solid-state ¹⁵N- and ¹⁹F-NMR structure analysis, however, showed that the KL backbone lies flat on the membrane surface under all conditions. We can thus refute any of the pore models and conclude that the KL peptides rather disrupt membranes by a carpet mechanism. The intriguing length-dependent optimum in activity can be fully explained by two counteracting effects, i.e., membrane binding versus amyloid formation. Very short KL peptides are inactive, because they are unable to bind to the lipid bilayer as flexible β-strands, whereas very long peptides are inactive due to vigorous pre-aggregation into β-sheets in solution.

A Second Life for MAP, a Model Amphipathic Peptide

Cell-penetrating peptides (CPP) have been shown to be efficient in the transport of cargoes into the cells, namely siRNA and DNA, proteins and peptides, and in some cases, small therapeutics. These peptides have emerged as a solution to increase drug concentrations in different tissues and various cell types, therefore having a relevant therapeutic relevance which led to clinical trials. One of them, MAP, is a model amphipathic peptide with an α-helical conformation and both hydrophilic and hydrophobic residues in opposite sides of the helix. It is composed of a mixture of alanines, leucines, and lysines (KLALKLALKALKAALKLA). The CPP MAP has the ability to translocate oligonucleotides, peptides and small proteins. However, taking advantage of its unique properties, in recent years innovative concepts were developed, such as in silico studies of modelling with receptors, coupling and repurposing drugs in the central nervous system and oncology, or involving the construction of dual-drug delivery systems using nanoparticles. In addition to designs of MAP-linked vehicles and strategies to achieve highly effective yet less toxic chemotherapy, this review will be focused on unique molecular structure and how it determines its cellular activity, and also intends to address the most recent and frankly motivating issues for the future.

Antimicrobial Peptide Analogs From Scorpions: Modifications and Structure-Activity

The rapid development of multidrug-resistant pathogens against conventional antibiotics is a global public health problem. The irrational use of antibiotics has promoted therapeutic limitations against different infections, making research of new molecules that can be applied to treat infections necessary. Antimicrobial peptides (AMPs) are a class of promising antibiotic molecules as they present broad action spectrum, potent activity, and do not easily induce resistance. Several AMPs from scorpion venoms have been described as a potential source for the development of new drugs; however, some limitations to their application are also observed. Here, we describe strategies used in several approaches to optimize scorpion AMPs, addressing their primary sequence, biotechnological potential, and characteristics that should be considered when developing an AMP derived from scorpion venoms. In addition, this review may contribute towards improving the understanding of rationally designing new molecules, targeting functional AMPs that may have a therapeutic application.

Determination of the Relationships between the Chemical Structure and Antimicrobial Activity of a GAPDH-Related Fish Antimicrobial Peptide and Analogs Thereof

The structure–activity relationships and mode of action of synthesized glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-related antimicrobial peptides were investigated. Including the native skipjack tuna GAPDH-related peptide (SJGAP) of 32 amino acid residues (model for the study), 8 different peptide analogs were designed and synthesized to study the impact of net charge, hydrophobicity, amphipathicity, and secondary structure on both antibacterial and antifungal activities. A net positive charge increase, by the substitution of anionic residues or C-terminal amidation, improved the antimicrobial activity of the SJGAP analogs (minimal inhibitory concentrations of 16–64 μg/mL), whereas the alpha helix content, as determined by circular dichroism, did not have a very definite impact. The hydrophobicity of the peptides was also found to be important, especially for the improvement of antifungal activity. Membrane permeabilization assays showed that the active peptides induced significant cytoplasmic membrane permeabilization in the bacteria and yeast tested, but that this permeabilization did not cause leakage of 260 nm-absorbing intracellular material. This points to a mixed mode of action involving both membrane pore formation and targeting of intracellular components. This study is the first to highlight the links between the physicochemical properties, secondary structure, antimicrobial activity, and mechanism of action of antimicrobial peptides from scombrids or homologous to GAPDH.

Application of the All-Hydrocarbon Stapling Technique in the Design of Membrane-Active Peptides

The threats of drug resistance and new emerging pathogens have led to an urgent need to develop alternative treatment therapies. Recently, considerable research efforts have focused on membrane-active peptides (MAPs), a category of peptides in drug discovery with antimicrobial, anticancer, and cell penetration activities that have demonstrated their potential to be multifunctional agents. Nonetheless, natural MAPs have encountered various disadvantages, which mainly include poor bioavailability, the lack of a secondary structure in short peptides, and high production costs for long peptide sequences. Hence, an "all-hydrocarbon stapling system" has been applied to these peptides and proven to effectively stabilize the helical conformations, improving proteolytic resistance and increasing both the potency and the cell permeability. In this review, we summarized and categorized the advances made using this powerful technique in the development of stapled MAPs. Furthermore, outstanding issues and suggestions for future design within each subcategory were thoroughly discussed.

Process intensification for the continuous production of an antimicrobial peptide in stably-transformed Sf-9 insect cells

The antibiotic resistance crisis has prompted research into alternative candidates such as antimicrobial peptides (AMPs). However, the demand for such molecules can only be met by continuous production processes, which achieve high product yields and offer compatibility with the Quality-by-Design initiative by implementing process analytical technologies such as turbidimetry and dielectric spectroscopy. We developed batch and perfusion processes at the 2-L scale for the production of BR033, a cecropin-like AMP from Lucilia sericata, in stably-transformed polyclonal Sf-9 cells. This is the first time that BR033 has been expressed as a recombinant peptide. Process analytical technology facilitated the online monitoring and control of cell growth, viability and concentration. The perfusion process increased productivity by ~ 180% compared to the batch process and achieved a viable cell concentration of 1.1 × 10⁷ cells/mL. Acoustic separation enabled the consistent retention of 98.5–100% of the cells, viability was > 90.5%. The recombinant AMP was recovered from the culture broth by immobilized metal affinity chromatography and gel filtration and was able to inhibit the growth of Escherichia coli K12. These results demonstrate a successful, integrated approach for the development and intensification of a process from cloning to activity testing for the production of new biopharmaceutical candidates.

Antifungal activity and mode of action of synthetic peptides derived from the tick OsDef2 defensin

Candida albicans is the principal opportunistic fungal pathogen in nosocomial settings and resistance to antifungal drugs is on the rise. Antimicrobial peptides from natural sources are promising novel therapeutics against C. albicans. OsDef2 defensin was previously found to be active against only Gram-positive bacteria, whereas derived fragments Os and its cysteine-free analogue, Os-C, are active against Gram-positive and Gram-negative bacteria at low micromolar concentrations. In this study, OsDef2-derived analogues and fragments were screened for anticandidal activity with the aim to identify peptides with antifungal activity and in so doing obtain a better understanding of the structural requirements for activity and modes of action. Os, Os-C and Os(11-22)NH₂ , a Os-truncated carboxy-terminal-amidated fragment, had the most significant antifungal activities, with minimum fungicidal concentrations (MFCs) in the micromolar range (6-28 μM). C. albicans killing was rapid and occurred within 30-60 min. Further investigations showed all three peptides interacted with cell wall derived polysaccharides while both Os and Os(11-22)NH₂ permeabilized fungal liposomes. Confocal laser scanning microscopy confirmed that Os-C and Os(11-22)NH₂ could enter the cytosol of live cells and subsequent findings suggest that the uptake of Os and Os-C, in contrast to Os(11-22)NH₂ , is energy dependent. Although Os, Os-C and Os(11-22)NH₂ induced the production of reactive oxygen species (ROS), co-incubation with ascorbic acid revealed that only ROS generated by Os-C and to a lesser extent Os(11-22)NH₂ resulted in cell death. Overall, Os, Os-C and Os(11-22)NH₂ are promising candidacidal agents.

Membrane Interactions of Latarcins: Antimicrobial Peptides from Spider Venom

A group of seven peptides from spider venom with diverse sequences constitute the latarcin family. They have been described as membrane-active antibiotics, but their lipid interactions have not yet been addressed. Using circular dichroism and solid-state ¹⁵N-NMR, we systematically characterized and compared the conformation and helix alignment of all seven peptides in their membrane-bound state. These structural results could be correlated with activity assays (antimicrobial, hemolysis, fluorescence vesicle leakage). Functional synergy was not observed amongst any of the latarcins. In the presence of lipids, all peptides fold into amphiphilic α-helices as expected, the helices being either surface-bound or tilted in the bilayer. The most tilted peptide, Ltc2a, possesses a novel kind of amphiphilic profile with a coiled-coil-like hydrophobic strip and is the most aggressive of all. It indiscriminately permeabilizes natural membranes (antimicrobial, hemolysis) as well as artificial lipid bilayers through the segregation of anionic lipids and possibly enhanced motional averaging. Ltc1, Ltc3a, Ltc4a, and Ltc5a are efficient and selective in killing bacteria but without causing significant bilayer disturbance. They act rather slowly or may even translocate towards intracellular targets, suggesting more subtle lipid interactions. Ltc6a and Ltc7, finally, do not show much antimicrobial action but can nonetheless perturb model bilayers.

Anti-biofilm and anti-inflammatory effects of Lycosin-II isolated from spiders against multi-drug resistant bacteria

Currently, multidrug-resistant bacteria are rapidly increasing worldwide because of the misuse or overuse of antibiotics. In particular, few options exist for treating infections caused by long-persisting oxacillin-resistant strains and recently proliferating carbapenem-resistant strains. Therefore, alternative treatments are urgently needed. The antimicrobial peptide (AMP) Lycosin-II is a peptide consisting of 21 amino acids isolated from the venom of the spider Lycosa singoriensis. Lycosin-II showed strong antibacterial activity and biofilm inhibition effects against gram-positive and gram-negative bacteria including oxacillin-resistant Staphylococcus aureus (S. aureus) and meropenem-resistant Pseudomonas aeruginosa (P. aeruginosa) isolated from patients. In addition, Lycosin-II was not cytotoxic against human foreskin fibroblast Hs27 or hemolytic against sheep red blood cells at the concentration of which exerted antibacterial activity. The mechanism of action of Lycosin-II involves binding to lipoteichoic acid and lipopolysaccharide of gram-positive and gram-negative bacterial membranes, respectively, to destroy the bacterial membrane. Moreover, Lycosin-II showed anti-inflammatory effects by inhibiting the expression of pro-inflammatory cytokines that are increased during bacterial infection in Hs27 cells. These results suggest that Lycosin-II can serve as a therapeutic agent against infections with multidrug-resistant strains.

Platelet 3D Preservation Using a Novel Biomimetic Nanofiber Peptide for Reduced Apoptosis and Easy Storage

Human platelets (PLTs) are vulnerable to unfavorable conditions, and their adequate supply is limited by strict transportation conditions. We report here that PLTs preserved under three-dimensional (3D) conditions using novel biomimetic nanofiber peptides showed reduced apoptosis compared with classical PLTs stored at 22 °C and facilitated the storage and transportation of PLTs. The mechanism of PLT 3D preservation involves the formation of cross-links and a 3D nanofibrous network by a self-assembled peptide scaffold material at physiological conditions after initiation by triggers in plasma. PLTs adhere to the surface of the nanofibrous network to facilitate the 3D distribution of PLTs. The 3D microstructure, rheological properties, and effect on the inflammatory response and hemolysis were evaluated. Compared to traditional PLTs stored at 22 °C, PLTs subjected to 3D preservation showed similar morphology, number, aggregation activity, and reduced apoptosis. The detection of the reactive oxygen species (ROS) levels demonstrated that both reduced intracellular and mitochondrial ROS levels were correlated with reduced apoptosis. This study reveals a new 3D preservation method for PLTs based on the use of novel biomimetic nanofiber peptides that presents an attractive opportunity for various biomedical applications.

Chemical "Butterfly Effect" Explaining the Coordination Chemistry and Antimicrobial Properties of Clavanin Complexes

Can a minor difference in the nonmetal binding sequence of antimicrobial clavanins explain the drastic change in the coordination environment and antimicrobial efficiency? This study answers the question with a definite "yes", showing the details of the bioinorganic chemistry of Zn(II) and Cu(II) complexes with clavanins, histidine-rich, antimicrobial peptides from hemocytes of the tunicate Styela clava.

Evaluating the effect of dermaseptin S4 and its derivatives on multidrug-resistant bacterial strains and on the colon cancer cell line SW620

Dermaseptins are peptides found in the skin secretions of Phyllomedusinae frogs. These peptides exert a lytic action on various microorganisms and have no considerable hemolytic effect except dermaseptin S4 (DS4) which exhibits a powerful cytotoxic effect. Therefore, we synthesized several analogs of DS4 in an attempt to find molecules with a weak hemolytic effect and significant bioactivities. In this study, we performed the synthesis of truncated peptides by introducing C-terminal and N-terminal amino acid deletions of the native sequence. All peptide analogs, in comparison with parental peptide, were tested firstly on human red blood cells to work out their cytotoxicity, secondly on the multidrug-resistant bacteria by trying to find MICs, and finally on colon cancer tumor cell line SW620 using the MTT test so as to investigate the anti-proliferative effect. Our results showed that, on the one hand, the N terminus of the native peptide was necessary for the antibacterial activity and the anti-proliferative effect of the peptide. On the other hand, the hemolytic activity was more notable in the sequences broken down on the C-terminal side.

Antimicrobial Peptide Modifications against Clinically Isolated Antibiotic-Resistant Salmonella

Antimicrobial peptides are promising molecules to address the global antibiotic resistance problem, however, optimization to achieve favorable potency and safety is required. Here, a peptide-template modification approach was employed to design physicochemical variants based on net charge, hydrophobicity, enantiomer, and terminal group. All variants of the scorpion venom peptide BmKn-2 with amphipathic α-helical cationic structure exhibited an increased antibacterial potency when evaluated against multidrug-resistant Salmonella isolates at a MIC range of 4–8 µM. They revealed antibiofilm activity in a dose-dependent manner. Sheep red blood cells were used to evaluate hemolytic and cell selectivity properties. Peptide Kn2-5R-NH₂, dKn2-5R-NH₂, and 2F-Kn2-5R-NH₂ (variants with +6 charges carrying amidated C-terminus) showed stronger antibacterial activity than Kn2-5R (a variant with +5 charges bearing free-carboxyl group at C-terminus). Peptide dKn2-5R-NH₂ (d-enantiomer) exhibited slightly weaker antibacterial activity with much less hemolytic activity (higher hemolytic concentration 50) than Kn2-5R-NH₂ (l-enantiomer). Furthermore, peptide Kn2-5R with the least hydrophobicity had the lowest hemolytic activity and showed the highest specificity to Salmonella (the highest selectivity index). This study also explained the relationship of peptide physicochemical properties and bioactivities that would fulfill and accelerate progress in peptide antibiotic research and development.

A Novel Antimicrobial Peptides From Pine Needles of Pinus densiflora Sieb. et Zucc. Against Foodborne Bacteria

Pine needles are used in several East Asian countries as food or traditional medicine. It contains functional components that exhibit a wide spectrum of pharmacological effects such as antioxidant, antimicrobial, anti-diabetic, and anti-inflammatory activities. We determined and characterized the novel antimicrobial peptides (AMPs) isolated from Pinus densiflora Sieb. et Zucc. The four active pine-needle (PN) peptides showed antimicrobial activity against foodborne bacteria with minimum inhibitory concentration (MIC) values within the range of 8-128 μg/ml. PN peptides showed no detectable hemolytic activity or cytotoxicity at the antimicrobial concentrations. The N-terminal amino acid sequence of the PN5 was identified using Edman degradation and Antimicrobial Peptide Database (APD) homology analysis showed that it was not identical to any other plant peptide. This suggests that PN5 can serve as an alternative therapeutic agent to be used in the food industry.

Antisense peptide nucleic acid inhibits the growth of KPC-producing Klebsiella pneumoniae strain

Klebsiella pneumoniae causes common and severe hospital- and community-acquired infections with a high incidence of multidrug resistance (MDR) and mortality. In this study, we investigated the ability of the antisense peptide nucleic acids (PNA) conjugated to the (KFF)3K cell-penetrating peptide (CPP) to target the gyrA KPC-producing K. pneumoniae and inhibit bacterial growth in vitro. The inhibitory effect on gyrA gene was evaluated by measuring 16s gene amplification in KPC-producing K. pneumoniae treated with the antisense PNA conjugate. The hemolytic property of the antisense PNA conjugate was accessed toward mice red blood cells. Finally, molecular modeling and dynamics simulations analyses in aqueous solutions were performed to predict the PNA conformation alone in contact with DNA (gyrA gene sequence). PNA was capable of inhibiting bacterial growth at 50 μM, also reducing 16S gene amplification in 96.7%. Besides, PNA presented low hemolytic activity (21.1% hemolysis) at this same concentration. Bioinformatics analysis demonstrated that the structure of the PNA is stable in water without major changes in its secondary structure. The ability of PNA and its conjugated CPP ((KFF)3K) to inhibit bacterial growth demonstrates the potential of this new class of antibacterial agents, encouraging further in vivo studies to confirm its therapeutic efficacy.

Advances in Molecular Understanding of α-Helical Membrane-Active Peptides

Biological membranes separate the interior of cells or cellular compartments from their outer environments. This barrier function of membranes can be disrupted by membrane-active peptides, some of which can spontaneously penetrate through the membranes or open leaky transmembrane pores. However, the origin of their activity/toxicity is not sufficiently understood for the development of more potent peptides. To this day, there are no design rules that would be generally valid, and the role of individual amino acids tends to be sequence-specific.In this Account, we describe recent progress in understanding the design principles that govern the activity of membrane-active peptides. We focus on α-helical amphiphilic peptides and their ability to (1) translocate across phospholipid bilayers, (2) form transmembrane pores, or (3) act synergistically, i.e., to produce a significantly more potent effect in a mixture than the individual components.We refined the description of peptide translocation using computer simulations and demonstrated the effect of selected residues. Our simulations showed the necessity to explicitly include charged residues in the translocation description to correctly sample the membrane perturbations they can cause. Using this description, we calculated the translocation of helical peptides with and without the kink induced by the proline/glycine residue. The presence of the kink had no effect on the translocation barrier, but it decreased the peptide affinity to the membrane and reduced the peptide stability inside the membrane. Interestingly, the effects were mainly caused by the peptide's increased polarity, not the higher flexibility of the kink.Flexibility plays a crucial role in pore formation and affects distinct pore structures in different ways. The presence of a kink destabilizes barrel-stave pores, because the kink prevents the tight packing of peptides in the bundle, which is characteristic of the barrel-stave structure. In contrast, the kink facilitates the formation of toroidal pores, where the peptides are only loosely arranged and do not need to closely assemble. The exact position of the kink in the sequence further determines the preferred arrangement of peptides in the pore, i.e., an hourglass or U-shaped structure. In addition, we demonstrated that two self-associated (via termini) helical peptides could mimic the behavior of peptides with a helix-kink-helix motif.Finally, we review the recent findings on the peptide synergism of the archetypal mixture of Magainin 2 and PGLa peptides. We focused on a bacterial plasma membrane mimic that contains negatively charged lipids and lipids with negative intrinsic curvature. We showed that the synergistic action of peptides was highly dependent on the lipid composition. When the lipid composition and peptide/lipid ratios were changed, the systems exhibited more complex behavior than just the previously reported pore formation. We observed membrane adhesion, fusion, and even the formation of the sponge phase in this regime. Furthermore, enhanced adhesion/partitioning to the membrane was reported to be caused by lipid-induced peptide aggregation.In conclusion, the provided molecular insight into the complex behavior of membrane-active peptides provides clues for the design and modification of antimicrobial peptides or toxins.

Overlapping Properties of the Short Membrane-Active Peptide BP100 With (i) Polycationic TAT and (ii) α-helical Magainin Family Peptides

BP100 is a short, designer-made membrane-active peptide with multiple functionalities: antimicrobial, cell-penetrating, and fusogenic. Consisting of five lysines and 6 hydrophobic residues, BP100 was shown to bind to lipid bilayers as an amphipathic α-helix, but its mechanism of action remains unclear. With these features, BP100 embodies the characteristics of two distinctly different classes of membrane-active peptides, which have been studied in detail and where the mechanism of action is better understood. On the one hand, its amphiphilic helical structure is similar to the pore forming magainin family of antimicrobial peptides, though BP100 is much too short to span the membrane. On the other hand, its length and high charge density are reminiscent of the HIV-TAT family of cell penetrating peptides, for which inverted micelles have been postulated as translocation intermediates, amongst other mechanisms. Assays were performed to test the antimicrobial and hemolytic activity, the induced leakage and fusion of lipid vesicles, and cell uptake. From these results the functional profiles of BP100, HIV-TAT, and the magainin-like peptides magainin 2, PGLa, MSI-103, and MAP were determined and compared. It is observed that the activity of BP100 resembles most closely the much longer amphipathic α-helical magainin-like peptides, with high antimicrobial activity along with considerable fusogenic and hemolytic effects. In contrast, HIV-TAT shows almost no antimicrobial, fusogenic, or hemolytic effects. We conclude that the amphipathic helix of BP100 has a similar membrane-based activity as magainin-like peptides and may have a similar mechanism of action.

Rational design of antimicrobial peptides targeting Gram-negative bacteria

Membrane-targeting host antimicrobial peptides (AMPs) can kill or inhibit the growth of Gram-negative bacteria. However, the evolution of resistance among microbes poses a substantial barrier to the long-term utility of the host AMPs. Combining experiment and molecular dynamics simulations, we show that terminal carboxyl capping enhances both membrane insertion and antibacterial activity of an AMP called P1. Furthermore, we show that a bacterial strain with evolved resistance to this peptide becomes susceptible to P1 variants with either backbone capping or lysine-to-arginine substitutions. Our results suggest that cocktails of closely related AMPs may be useful in overcoming evolved resistance.

Interaction between Antimicrobial Peptide CM15 and a Model Cell Membrane Affected by CM15 Terminal Amidation and the Membrane Phase State

Antimicrobial peptides (AMPs) have been proposed as an effective class of antimicrobial agents against microorganisms. In this work, the interaction between an antimicrobial peptide, CM15, and a negatively charged phospholipid bilayer, DPPG, was studied via sum frequency generation (SFG) vibrational spectroscopy. Two structurally correlated characteristic variables were introduced to reveal the interaction mechanism/efficiency, i.e. C-terminal amidation and temperature variation (∼20 °C, room temperature, and ∼35 °C, close to human body temperature). Experimental results indicated that owing to the increased positive charge, C-terminal amidation resulted in rapid adsorption onto the bilayer surface and efficient disruption of the outer layer, exhibiting less ordered insertion orientation. The elevated temperature (from ∼20 °C to ∼35 °C) promoted the penetration of both the outer and inner leaflets by the peptides and finally led to the disruption of the whole bilayer owing to the enhanced fluidity of the bilayer. From the perspective of the interaction mechanism, this experimental study provides two practical cues to understand the disruption process of the negatively charged model biomembranes, which can lay the structural foundation for designing and developing high-efficiency antimicrobial peptides.

Improved Stability and Activity of a Marine Peptide-N6NH2 against Edwardsiella tarda and Its Preliminary Application in Fish

Edwardsiella tarda can cause fatal gastro-/extraintestinal diseases in fish and humans. Overuse of antibiotics has led to antibiotic resistance and contamination in the environment, which highlights the need to find new antimicrobial agents. In this study, the marine peptide-N6 was amidated at its C-terminus to generate N6NH2. The antibacterial activity of N6 and N6NH2 against E. tarda was evaluated in vitro and in vivo; their stability, toxicity and mode of action were also determined. Minimal inhibitory concentrations (MICs) of N6 and N6NH2 against E. tarda were 1.29–3.2 μM. Both N6 and N6NH2 killed bacteria by destroying the cell membrane of E. tarda and binding to lipopolysaccharide (LPS) and genomic DNA. In contrast with N6, N6NH2 improved the stability toward trypsin, reduced hemolysis (by 0.19% at a concentration of 256 μg/mL) and enhanced the ability to penetrate the bacterial outer and inner membrane. In the model of fish peritonitis caused by E. tarda, superior to norfloxacin, N6NH2 improved the survival rate of fish, reduced the bacterial load on the organs, alleviated the organ injury and regulated the immunity of the liver and kidney. These data suggest that the marine peptide N6NH2 may be a candidate for novel antimicrobial agents against E. tarda infections.

Design of antimicrobial and cytolytic peptides by computational analysis of bacterial, algal, and invertebrate proteomes

The increase of antibiotic resistance in bacterial species has raised the need to search for novel antimicrobial molecules. Antimicrobial peptides are molecules that commonly display an amphipathic character. In this work, we developed a computational strategy to search for new peptide sequences within the proteome of any organism that includes in-house developed software and the use of artificial intelligence tools available online. Eleven peptides were selected after analyzing 63,343 proteins from the proteomes of bacteria, algae and invertebrates. Then, we validated the results by means of several assays which were carried out against five (5) pathogenic bacterial species and two (2) cancer cell lines. As a result, we found that ten of the peptides were antimicrobial, with minimum inhibitory concentration values between 4 and [Formula: see text]. Furthermore, two of the more active peptides were also cytotoxic to human red blood cells and cancer cells. In general, the antimicrobial peptides we discovered produced damage on the bacterial cell membrane that included membrane wrinkling, cell blebbing, and leakage of cytoplasmic material. Based on these results, we concluded that the computational approach proposed for finding sequences encrypted in proteins is appropriate for the discovery of selective and non-selective antimicrobial and anticancer peptides.

Morphing of Amphipathic Helices to Explore the Activity and Selectivity of Membranolytic Antimicrobial Peptides

Naturally occurring membranolytic antimicrobial peptides (AMPs) are rarely cell-type selective and highly potent at the same time. Template-based peptide design can be used to generate AMPs with improved properties de novo. Following this approach, 18 linear peptides were obtained by computationally morphing the natural AMP Aurein 2.2d2 GLFDIVKKVVGALG into the synthetic model AMP KLLKLLKKLLKLLK. Eleven of the 18 chimeric designs inhibited the growth of Staphylococcus aureus, and six peptides were tested and found to be active against one resistant pathogenic strain or more. One of the peptides was broadly active against bacterial and fungal pathogens without exhibiting toxicity to certain human cell lines. Solution nuclear magnetic resonance and molecular dynamics simulation suggested an oblique-oriented membrane insertion mechanism of this helical de novo peptide. Temperature-resolved circular dichroism spectroscopy pointed to conformational flexibility as an essential feature of cell-type selective AMPs.

The Spectrum of Design Solutions for Improving the Activity-Selectivity Product of Peptide Antibiotics against Multidrug-Resistant Bacteria and Prostate Cancer PC-3 Cells

The link between the antimicrobial and anticancer activity of peptides has long been studied, and the number of peptides identified with both activities has recently increased considerably. In this work, we hypothesized that designed peptides with a wide spectrum of selective antimicrobial activity will also have anticancer activity, and tested this hypothesis with newly designed peptides. The spectrum of peptides, used as partial or full design templates, ranged from cell-penetrating peptides and putative bacteriocin to those from the simplest animals (placozoans) and the Chordata phylum (anurans). We applied custom computational tools to predict amino acid substitutions, conferring the increased product of bacteriostatic activity and selectivity. Experiments confirmed that better overall performance was achieved with respect to that of initial templates. Nine of our synthesized helical peptides had excellent bactericidal activity against both standard and multidrug-resistant bacteria. These peptides were then compared to a known anticancer peptide polybia-MP1, for their ability to kill prostate cancer cells and dermal primary fibroblasts. The therapeutic index was higher for seven of our peptides, and anticancer activity stronger for all of them. In conclusion, the peptides that we designed for selective antimicrobial activity also have promising potential for anticancer applications.

OctoPartenopin: Identification and Preliminary Characterization of a Novel Antimicrobial Peptide from the Suckers of Octopus vulgaris

Microorganism resistance to conventional antibiotics represents one of the major global health concerns. This paper focuses on a peptide (OctoPartenopin) extracted from suckers of Octopus vulgaris; bioassay-guided chromatographic fractionation was used to identify this sequence, which holds significant antibacterial activity against Gram-positive and Gram-negative bacteria. OctoPartenopin is encrypted within the calponin sequence and was associated with the high levels of proteolytic activity already reported in octopus arm suckers. We synthesized the parent peptide and four analogues; all peptide were tested for their antibacterial and antibiofilm activities. Preliminary antibiofilm experiments showed that that one of the analogues had the best activity in both inhibition and eradication of biofilm of all three microorganisms tested. The occurrence of OctoPartenopin in arm suckers provided novel speculative information on animal behavior, as concerns maternal care of fertilized eggs. Our results highlight that suckers are a rich source of multifaceted peptides to develop alternative antimicrobial agents and food preservatives.

Phosphate-dependent aggregation of [KL]n peptides affects their membranolytic activity

In this study, we investigate how the length of amphiphilic β-sheet forming peptides affects their interaction with membranes. Four polycationic model peptides with lengths from 6 to 18 amino acids were constructed from simple Lys-Leu repeats, giving [KL]_n=3,5,7,9. We found that (1) they exhibit a pronounced antimicrobial activity with an intriguing length dependent maximum for [KL]₅ with 10 amino acids; (2) their hemolytic effect, on the other hand, increases steadily with peptide length. CD analysis (3) and TEM (4) show that all peptides-except for the short [KL]₃-aggregate into amyloid-like fibrils in the presence of phosphate ions, which in turn has a critical effect on the results in (1) and (2). In fact, (5) vesicle leakage reveals an intrinsic membrane-perturbing activity (at constant peptide mass) of [KL]₅ > [KL]₉ > [KL]₇ in phosphate buffer, which changes to [KL]₅ ≈ [KL]₇ ≈ [KL]₉ in PIPES. A specific interaction with phosphate ions thus explains the subtle balance between two counteracting effects: phosphate-induced unproductive pre-aggregation in solution versus monomeric membrane binding and vigorous lipid perturbation due to self-assembly of the bound peptides within the bilayer. This knowledge can now be used to control and optimize the peptides in further applications.

Chiral supramolecular architecture of stable transmembrane pores formed by an α-helical antibiotic peptide in the presence of lyso-lipids

The amphipathic α-helical antimicrobial peptide MSI-103 (aka KIA21) can form stable transmembrane pores when the bilayer takes on a positive spontaneous curvature, e.g. by the addition of lyso-lipids. Solid-state 31P- and 15N-NMR demonstrated an enrichment of lyso-lipids in these toroidal wormholes. Anionic lyso-lipids provided additional stabilization by electrostatic interactions with the cationic peptides. The remaining lipid matrix did not affect the nature of the pore, as peptides maintained the same orientation independent of lipid charge, and a change in membrane thickness did not considerably affect their tilt angle. Under optimized conditions (i.e. in the presence of lyso-lipids and appropriate bilayer thickness), stable and well-aligned pores could be obtained for solid-state 2H-NMR analysis. These data revealed for the first time the complete 3D alignment of this representative amphiphilic peptide in fluid membranes, which is compatible with either monomeric helices as constituents, or left-handed supercoiled dimers as building blocks from which the overall toroidal wormhole is assembled.

What Makes a Good Pore Former: A Study of Synthetic Melittin Derivatives

Pore formation by membrane-active peptides, naturally encountered in innate immunity and infection, could have important medical and technological applications. Recently, the well-studied lytic peptide melittin has formed the basis for the development of combinatorial libraries from which potent pore-forming peptides have been derived, optimized to work under different conditions. We investigate three such peptides, macrolittin70, which is most active at neutral pH; pHD15, which is active only at low pH; and MelP5_Δ6, which was rationally designed to be active at low pH but formed only small pores. There are three, six, and six acidic residues in macrolittin70, pHD15, and MelP5_Δ6, respectively. We perform multi-microsecond simulations in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) of hexamers of these peptides starting from transmembrane orientations at neutral pH (all residues at standard protonation), low pH (acidic residues and His protonated), and highly acidic environments in which C-termini are also protonated. Previous simulations of the parent peptides melittin and MelP5 in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are repeated in POPC. We find that the most potent pore-forming peptides exhibit strong interpeptide interactions, including salt bridges, H-bonds, and polar interactions. Protonation of the C-terminus promotes helicity and pore size. The proximity of the peptides allows fewer lipid headgroups to line the pores than in previous simulations, making the pores intermediate between barrel stave and toroidal. Based on these structures and geometrical arguments, we attempt to rationalize the factors that under different conditions can increase or decrease pore stability and propose mutations that could be tested experimentally.

Peptidomics Approaches for the Identification of Bioactive Molecules from Diaphorina citri

Huanglongbing (HLB), a deadly citrus disease, is primarily associated with Candidatus Liberibacter asiaticus (CLas) and spread by the hemipteran insect Diaphorina citri. Control strategies to combat HLB are urgently needed. In this work, we developed and compared workflows for the extraction of the D. citri peptidome, a dynamic set of polypeptides produced by proteolysis and other cellular processes. High-resolution mass spectrometry revealed bias among methods reflecting the physiochemical properties of the peptides: while TCA/acetone-based methods resulted in enrichment of C-terminally amidated peptides, a modification characteristic of bioactive peptides, larger peptides were overrepresented in the aqueous phase of chloroform/methanol extracts, possibly indicative of reduced co-analytical degradation during sample preparation. Parallel reaction monitoring (PRM) was used to validate the structure and upregulation of peptides derived from hemocyanin, a D. citri immune system protein, in insects reared on healthy and CLas-infected trees. Mining of the data sets also revealed 122 candidate neuropeptides, including PK/PBAN family neuropeptides and kinins, biostable analogs of which have known insecticidal properties. Taken together, this information yields new, in-depth insights into peptidomics methodology. Additionally, the putative neuropeptides identified may lead to psyllid mortality if applied to or expressed in citrus, consequently blocking the spread of HLB disease in citrus groves.

Novel Ocellatin Peptides Mitigate LPS-induced ROS Formation and NF-kB Activation in Microglia and Hippocampal Neurons

Cutaneous secretions of amphibians have bioactive compounds, such as peptides, with potential for biotechnological applications. Therefore, this study aimed to determine the primary structure and investigate peptides obtained from the cutaneous secretions of the amphibian, Leptodactylus vastus, as a source of bioactive molecules. The peptides obtained possessed the amino acid sequences, GVVDILKGAAKDLAGH and GVVDILKGAAKDLAGHLASKV, with monoisotopic masses of [M + H]^± = 1563.8 Da and [M + H]^± = 2062.4 Da, respectively. The molecules were characterized as peptides of the class of ocellatins and were named as Ocellatin-K1(1-16) and Ocellatin-K1(1-21). Functional analysis revealed that Ocellatin-K1(1-16) and Ocellatin-K1(1-21) showed weak antibacterial activity. However, treatment of mice with these ocellatins reduced the nitrite and malondialdehyde content. Moreover, superoxide dismutase enzymatic activity and glutathione concentration were increased in the hippocampus of mice. In addition, Ocellatin-K1(1-16) and Ocellatin-K1(1-21) were effective in impairing lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) formation and NF-kB activation in living microglia. We incubated hippocampal neurons with microglial conditioned media treated with LPS and LPS in the presence of Ocellatin-K1(1-16) and Ocellatin-K1(1-21) and observed that both peptides reduced the oxidative stress in hippocampal neurons. Furthermore, these ocellatins demonstrated low cytotoxicity towards erythrocytes. These functional properties suggest possible to neuromodulatory therapeutic applications.

Best of Two Worlds? How MD Simulations of Amphiphilic Helical Peptides in Membranes Can Complement Data from Oriented Solid-State NMR

The membrane alignment of helical amphiphilic peptides in oriented phospholipid bilayers can be obtained as ensemble and time averages from solid state ²H NMR by fitting the quadrupolar splittings to ideal α-helices. At the same time, molecular dynamics (MD) simulations can provide atomistic insight into peptide-membrane systems. Here, we evaluate the potential of MD simulations to complement the experimental NMR data that is available on three exemplary systems: the natural antimicrobial peptide PGLa and the two designer-made peptides MSI-103 and KIA14, whose sequences were derived from PGLa. Each peptide was simulated for 1 μs in a DMPC lipid bilayer. We calculated from the MD simulations the local angles which define the side chain geometry with respect to the peptide helix. The peptide orientation was then calculated (i) directly from the simulation, (ii) from back-calculated MD-derived NMR splittings, and (iii) from experimental ²H NMR splittings. Our findings are that (1) the membrane orientation and secondary structure of the peptides found in the NMR analysis are generally well reproduced by the simulations; (2) the geometry of the side chains with respect to the helix backbone can deviate significantly from the ideal structure depending on the specific residue, but on average all side chains have the same orientation; and (3) for all of our peptides, the azimuthal rotation angle found from the MD-derived splittings is about 15° smaller than the experimental value.