Mining the tree of life: Host defense peptides as antiviral therapeutics.

Discovering new therapeutics for human viral diseases is important for combatting emerging infectious viruses and omnipresent circulating viruses as well as those that can become resistant to the drugs we currently have available. The innate host defense peptide (HDP) repertoire present in animals is a wealth of potential antimicrobial agents that could be mined to meet these needs. While much of the body of research regarding HDPs is in the context of bacteria, there is increasing evidence that they can be an effective source for antivirals. Peptides can be identified in a number of ways, including eco-conservation-minded approaches. Those shown to have antiviral properties can be modified to exhibit desired properties as the relationship between structure and function is elucidated and then developed into therapeutics for human use. This review looks at the discovery and therapeutic potential of HDPs for human viral infections.

Expression and purification of the native C-amidated antimicrobial peptide maculatin 1.1.

Maculatin 1.1 (Mac1) is an antimicrobial peptide (AMP) from an Australian tree frog and exhibits low micromolar activity against Gram-positive bacteria. The antimicrobial properties of Mac1 are linked to its disruption of bacterial lipid membranes, which has been studied extensively by in vitro nuclear magnetic resonance (NMR) spectroscopy and biophysical approaches. Although in vivo NMR has recently proven effective in probing peptide-lipid interplay in live bacterial cells, direct structural characterisation of AMPs has been prohibited by low sensitivity and overwhelming background noise. To overcome this issue, we report a recombinant expression protocol to produce isotopically enriched Mac1. We utilized a double-fusion construct to alleviate toxicity against the Escherichia coli host and generate the native N-free and C-amidated termini Mac1 peptide. The SUMO and intein tags allowed native N-terminus and C-terminal amidation, respectively, to be achieved in a one-pot reaction. The protocol yielded 0.1 mg/L of native, uniformly 15 N-labelled, Mac1, which possessed identical structure and activity to peptide obtained by solid-phase peptide synthesis.

Net charge tuning modulates the antiplasmodial and anticancer properties of peptides derived from scorpion venom.

VmCT1, a linear helical antimicrobial peptide isolated from the venom of the scorpion Vaejovis mexicanus, displays broad spectrum antimicrobial activity against bacteria, fungi, and protozoa. Analogs derived from this peptide containing single Arg-substitutions have been shown to increase antimicrobial and antiparasitic activities against Trypanossoma cruzi. Here, we tested these analogs against malaria, an infectious disease caused by Plasmodium protozoa, and assessed their antitumoral properties. Specifically, we tested VmCT1 synthetic variants [Arg]3 -VmCT1-NH2 , [Arg]7 -VmCT1-NH2 , and [Arg]11 -VmCT1-NH2 , against Plasmodium gallinaceum sporozoites and MCF-7 mammary cancer cells. Our screen identified peptides [Arg]3 -VmCT1-NH2 and [Arg]7 -VmCT1-NH2 as potent antiplasmodial agents (IC50 of 0.57 and 0.51 µmol L-1 , respectively), whereas [Arg]11 -VmCT1-NH2 did not show activity against P. gallinaceum sporozoites. Interestingly, all peptides presented activity against MCF-7 and displayed lower cytotoxicity toward healthy cells. We demonstrate that increasing the net positive charge of VmCT1, through arginine substitutions, modulates the biological properties of this peptide family yielding novel antiplasmodial and antitumoral molecules.

Identification of a novel proline-rich antimicrobial protein from the hemolymph of Antheraea mylitta.

Antimicrobial proteins (AMPs) are small, cationic proteins that exhibit activity against bacteria, viruses, parasites, fungi as well as boost host-specific innate immune responses. Insects produce these AMPs in the fat body and hemocytes, and release them into the hemolymph upon microbial infection. Hemolymph was collected from the bacterially immunized fifth instar larvae of tasar silkworm, Antheraea mylitta, and an AMP was purified by organic solvent extraction followed by size exclusion and reverse-phase high-pressure liquid chromatography. The purity of AMP was confirmed by thin-layer chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The molecular mass was determined by matrix-assisted laser desorption ionization-time of flight mass spectrometry as 14 kDa, and hence designated as AmAMP14. Peptide mass fingerprinting of trypsin-digested AmAMP14 followed by de novo sequencing of one peptide fragment by tandem mass spectrometry analysis revealed the amino acid sequences as CTSPKQCLPPCK. No homology was found in the database search and indicates it as a novel AMP. The minimum inhibitory concentration of the purified AmAMP14 was determined against Escherichia coli, Staphylococcus aureus, and Candida albicans as 30, 60, and 30 µg/ml, respectively. Electron microscopic examination of the AmAMP14-treated cells revealed membrane damage and release of cytoplasmic contents. All these results suggest the production of a novel 14 kDa AMP in the hemolymph of A. mylitta to provide defense against microbial infection.

Evaluation of antimicrobial and anticancer activities of three peptides identified from the skin secretion of Hylarana latouchii.

The skins of frogs of the family Ranidae are particularly rich sources of biologically active peptides, among which antimicrobial peptides (AMPs) constitute the major portion. Some of these have attracted the interest of researchers because they possess both antimicrobial and anticancer activities. In this study, with 'shotgun' cloning and MS/MS fragmentation, three AMPs, homologues of family brevinin-1 (brevinin-1HL), and temporin (temporin-HLa and temporin-HLb), were discovered from the skin secretion of the broad-folded frog, Hylarana latouchii. They exhibited various degrees of antimicrobial and antibiofilm activities against test microorganisms and hemolysis on horse erythrocytes. It was found that they could induce bacteria death through disrupting cell membranes and binding to bacterial DNA. In addition, they also showed different potencies towards human cancer cell lines. The secondary structure and physicochemical properties of each peptide were investigated to preliminarily reveal their structure-activity relationships. Circular dichroism spectrometry showed that they all adopted a canonical α-helical conformation in membrane-mimetic solvents. Notably, the prepropeptide of brevinin-1HL from H. latouchii was highly identical to that of brevinin-1GHd from Hylarana guentheri, indicating a close relationship between these two species. Accordingly, this study provides candidates for the design of novel anti-infective and antineoplastic agents to fight multidrug-resistant bacteria and malignant tumors and also offers additional clues for the taxonomy of ranid frogs.

A Crustin from Hydrothermal Vent Shrimp: Antimicrobial Activity and Mechanism.

Crustin is a type of antimicrobial peptide and plays an important role in the innate immunity of arthropods. We report here the identification and characterization of a crustin (named Crus1) from the shrimp Rimicaris sp. inhabiting the deep-sea hydrothermal vent in Manus Basin (Papua New Guinea). Crus1 shares the highest identity (51.76%) with a Type I crustin of Penaeus vannamei and possesses a whey acidic protein (WAP) domain, which contains eight cysteine residues that form the conserved 'four-disulfide core' structure. Recombinant Crus1 (rCrus1) bound to peptidoglycan and lipoteichoic acid, and effectively killed Gram-positive bacteria in a manner that was dependent on pH, temperature, and disulfide linkage. rCrus1 induced membrane leakage and structure damage in the target bacteria, but had no effect on bacterial protoplasts. Serine substitution of each of the 8 Cys residues in the WAP domain did not affect the bacterial binding capacity but completely abolished the bactericidal activity of rCrus1. These results provide new insights into the characteristic and mechanism of the antimicrobial activity of deep sea crustins.

New Hopes for Drugs against COVID-19 Come from the Sea.

The latest chapter of the historic battle of humans against pathogenic microbes is the severe acute respiratory syndrome (SARS)-like coronavirus-2 (SARS-CoV-2), responsible for COVID-19, a respiratory disease declared a global pandemic by the WHO on March 11, 2020 [...].

Antibacterial activity and mechanism of the cell-penetrating peptide CF-14 on the gram-negative bacteria, Escherichia coli.

In the present study, we characterized CF-14, a novel antimicrobial peptide derived from the catfish skin mucus. The objective of this study was to explore the antimicrobial mechanism of CF-14 against Escherichia coli. The agar-diffusion assay and the microdilution method were used to evaluate the antimicrobial activity and the minimum inhibitory concentration (MIC) of CF-14 against E. coli, respectively. In addition, the absorbance of the bacterial suspension filtrate at 260 nm was measured to quantify the leakage of bacterial cytoplasmic components. The bacterial morphological changes were observed by scanning electron microscopy, while confocal microscopy was used to investigate the localization site of CF-14 in E.coli. The DNA binding ability of CF-14 was evaluated using gel retardation assay and the binding of CF-14 to DnaK was evaluated using Discovery Studio. The results demonstrated that CF-14 exhibited strong antimicrobial activity against E.coli with an MIC of 31.3 µg/mL. Unlike common cationic anti-microbial peptides (AMPs) that target the cellmembrane, CF-14 penetrated the E.coli cell membrane and induced only minormembrane perturbations. Furthermore, the antimicrobial mechanism of CF-14 against E.coli involved DNA binding and competitive inhibition of bacterial DnaK. Finally, by deleting or replacing the amino acid sequence, the antibacterial activity of CF-14 was affected, which helped the optimization of amino acid sequence. Therefore, CF-14 can be a potential antimicrobial peptide.

Membrane disruptive antimicrobial potential of NK-lysin from yellow catfish (Pelteobagrus fulvidraco).

NK-lysins, a type of broad-spectrum antimicrobial peptide (AMP), act as an essential effector of innate defense against microbial attack in higher vertebrates and so in fish. The present study delineates the structural and functional characterization of NK-lysin from yellow catfish (Pelteobagrus fulvidrac) (Pelteobagrus fulvidraco). PfNK-lysin encodes a 153-residue peptide, which displays the hallmark features of other known NK-lysins with the ordered array of six well-conserved cysteine residues and five-exon/four-intron structure. It was found to be ubiquitous in tissues, being detected most abundantly in gill and head kidney. In vivo exposure to stimuli (LPS, PolyI:C, and Edwardsiella ictaluri) induced PfNK-lysin expression in head kidney and spleen. Synthetic PfNK-lysin-derived peptide exhibited in vitro bactericidal potency against both Gram-positive and Gram-negative bacteria, with the highest inhibitory effect on pathogen Edwardsiella ictaluri. Fluorescence microscopy and scanning electron microscopy further confirmed its capacity to cause damage to the bacterial plasma membrane. Taken together, these data suggest that PfNK-lysin might participate in antimicrobial defense of yellow catfish by membrane-disruptive action.

Expression of T9W in Pichia pastoris and the protective roles of T9W in ICR Mice.

BACKGROUND: The purpose of this paper is to express the novel α-helical peptide T9W more efficiently using the Pichia pastoris expression system and to examine the role of T9W in ICR mice. RESULTS: The novel antimicrobial peptide T9W was expressed in P. pastoris X-33 by using the vector pPICZαA. Approximately 13 mg/L T9W was secreted from the culture and purified. The expressed peptide has similar activity to the synthetic peptide. ICR female mice challenged with P. aeruginosa 27853 at the LD100 were treated with T9W and CPFX. The results showed that the secretion of inflammatory cytokines and lung damage was significantly reduced by the treatment group, and the protective response was equivalent between T9W and ciprofloxacin-treated mice. CONCLUSION: T9W was expressed in P. pastoris X-33 via the methanol-inducible vector pPICZαA and exhibited the same biological activity as synthetic T9W. T9W can alleviate damage to mice caused by P. aeruginosa.

The First Genome Survey of the Antarctic Krill (Euphausia superba) Provides a Valuable Genetic Resource for Polar Biomedical Research.

The world-famous Antarctic krill (Euphausia superba) plays a fundamental role in the Antarctic food chain. It resides in cold environments with the most abundant biomass to support the Antarctic ecology and fisheries. Here, we performed the first genome survey of the Antarctic krill, with genomic evidence for its estimated genome size of 42.1 gigabases (Gb). Such a large genome, however, is beyond our present capability to obtain a good assembly, although our sequencing data are a valuable genetic resource for subsequent polar biomedical research. We extracted 13 typical protein-coding gene sequences of the mitochondrial genome and analyzed simple sequence repeats (SSRs), which are useful for species identification and origin determination. Meanwhile, we conducted a high-throughput comparative identification of putative antimicrobial peptides (AMPs) and antihypertensive peptides (AHTPs) from whole-body transcriptomes of the Antarctic krill and its well-known counterpart, the whiteleg shrimp (Penaeus vannamei; resident in warm waters). Related data revealed that AMPs/AMP precursors and AHTPs were generally conserved, with interesting variations between the two crustacean species. In summary, as the first report of estimated genome size of the Antarctic krill, our present genome survey data provide a foundation for further biological research into this polar species. Our preliminary investigations on bioactive peptides will bring a new perspective for the in-depth development of novel marine drugs.

Alterins Produced by Oyster-Associated Pseudoalteromonas Are Antibacterial Cyclolipopeptides with LPS-Binding Activity.

Discovery after discovery, host-associated microbiota reveal a growing list of positive effects on host homeostasis by contributing to host nutrition, improving hosts' immune systems and protecting hosts against pathogens. In that context, a collection of oyster associated bacteria producing antibacterial compounds have been established to evaluate their role in non-host-derived immunity. Here, we described alterins; potent anti-Gram negative compounds produced by Pseudoalteromonas hCg-6 and hCg-42 isolated from different healthy oyster hemolymph. The strains hCg-6 and hCg-42 produce a set of at least seven antibacterial compounds, ranging from 926 to 982 Da structurally characterized as cyclolipopeptides (CLPs). Alterins share the same cationic heptapeptidic cycle connected via an amido bond to different hydrophobic hydrocarbon tails. Their MICs disclosed a potent antibacterial activity directed against Gram-negative bacteria including oyster and human pathogens that may confer a beneficial defense mechanism to the host but also represents an untapped source of new antibiotics. The alterins' mechanisms of action have been deciphered: after binding to lipopolysaccharides (LPS), alterins provoke a membrane depolarization and permeabilization leading to bacterial lysis. As hCg-6 and hCg-42 produced a set of natural derivatives, the structure/activity relationship linked to the carbon tail is clarified. We showed that the hydrocarbon tail determines the LPS-binding properties of alterins and consequently their antibacterial activities. Its length and saturation seem to play a major role in this interaction.

Isolation and Characterization of Antimicrobial Peptides with Unusual Disulfide Connectivity from the Colonial Ascidian Synoicum turgens.

This study reports the isolation of two novel cysteine-rich antibacterial peptides, turgencin A and turgencin B, along with their oxidized derivatives, from the Arctic marine colonial ascidian Synoicum turgens. The peptides are post-translationally modified, containing six cysteines with an unusual disulfide connectivity of Cys1-Cys6, Cys2-Cys5, and Cys3-Cys4 and an amidated C-terminus. Furthermore, the peptides contain methionine residues resulting in the isolation of peptides with different degrees of oxidation. The most potent peptide, turgencin AMox1 with one oxidized methionine, displayed antimicrobial activity against both Gram-negative and Gram-positive bacteria with a minimum inhibitory concentration (MIC) as low as 0.4 µM against selected bacterial strains. In addition, the peptide inhibited the growth of the melanoma cancer cell line A2058 (IC50 = 1.4 µM) and the human fibroblast cell line MRC-5 (IC50 = 4.8 µM). The results from this study show that natural peptides isolated from marine tunicates have the potential to be promising drug leads.

Antimicrobial Peptide TP4 Targets Mitochondrial Adenine Nucleotide Translocator 2.

Tilapia piscidin (TP) 4 is an antimicrobial peptide derived from Nile tilapia (Oreochromis niloticus), which shows broad-spectrum antibacterial activity and excellent cancer-killing ability in vitro and in vivo. Like many other antimicrobial peptides, TP4 treatment causes mitochondrial toxicity in cancer cells. However, the molecular mechanisms underlying TP4 targeting of mitochondria remain unclear. In this study, we used a pull-down assay on A549 cell lysates combined with LC-MS/MS to discover that TP4 targets adenine nucleotide translocator (ANT) 2, a protein essential for adenine nucleotide exchange across the inner membrane. We further showed that TP4 accumulates in mitochondria and colocalizes with ANT2. Moreover, molecular docking studies showed that the interaction requires Phe1, Ile2, His3, His4, Ser11, Lys14, His17, Arg21, Arg24 and Arg25 residues in TP4 and key residues within the cavity of ANT2. These findings suggest a mechanism by which TP4 may induce mitochondrial dysfunction to disrupt cellular energy metabolism.

Microwave-assisted extraction (MAE) combined with gas chromatography-mass spectrometry (GC-MS) for determination of volatile small molecules to evaluate compatibility of antimicrobial peptide PL-5 spray with packaging materials.

A simple and efficient method involving microwave-assisted extraction (MAE) combined with GC-MS was established to determine 1,3-di-tert-butylbenzene (DBB), 2,4-di-tert-butylphenol (DBP), 3,5-di-tert-butyl-4-hydroxybenzaldehyde (DBHBA) for evaluating the compatibility of antimicrobial peptide PL-5 spray with drug-packaging materials. In this study, the antimicrobial peptide PL-5 spray was purified using a Welchrom C18 column, and the high-density polyethylene spray bottle with liquid collection tube was first mixed with absolute ethanol, which would be subjected to MAE for further measurement by GC-MS. Various experimental parameters were systematically optimized, and good linearities were obtained within the range of 0.05-1.00 µg/mL for DBB and DBHBA and 0.50-10.00 µg/mL for DBP, with limits of detection (LODs) of 0.99 ng/mL (DBB), 16.34 ng/mL (DBP), and 1.64 ng/mL (DBHBA). Satisfactory recoveries that ranged from 96.0% to 107.2% were acquired, and the relative standard deviation was ≤ 4.7%. The results showed that the maximum daily usage of DBB, DBP, and DBHBA was 9.859, 163.445, and 16.399 ng, respectively, which was far below the corresponding permitted daily exposure values according to the safety assessment, indicating that the migration of analytes did not bring any potential safety risk. The compatibility between the drug and the packaging materials was favorable.

Characterization and Identification of Natural Antimicrobial Peptides on Different Organisms.

Because of the rapid development of multidrug resistance, conventional antibiotics cannot kill pathogenic bacteria efficiently. New antibiotic treatments such as antimicrobial peptides (AMPs) can provide a possible solution to the antibiotic-resistance crisis. However, the identification of AMPs using experimental methods is expensive and time-consuming. Meanwhile, few studies use amino acid compositions (AACs) and physicochemical properties with different sequence lengths against different organisms to predict AMPs. Therefore, the major purpose of this study is to identify AMPs on seven categories of organisms, including amphibians, humans, fish, insects, plants, bacteria, and mammals. According to the one-rule attribute evaluation, the selected features were used to construct the predictive models based on the random forest algorithm. Compared to the accuracies of iAMP-2L (a web-server for identifying AMPs and their functional types), ADAM (a database of AMP), and MLAMP (a multi-label AMP classifier), the proposed method yielded higher than 92% in predicting AMPs on each category. Additionally, the sensitivities of the proposed models in the prediction of AMPs of seven organisms were higher than that of all other tools. Furthermore, several physicochemical properties (charge, hydrophobicity, polarity, polarizability, secondary structure, normalized van der Waals volume, and solvent accessibility) of AMPs were investigated according to their sequence lengths. As a result, the proposed method is a practical means to complement the existing tools in the characterization and identification of AMPs in different organisms.

Cyanobacteria and Eukaryotic Microalgae as Emerging Sources of Antibacterial Peptides.

Cyanobacteria and microalgae are oxygen-producing photosynthetic unicellular organisms encompassing a great diversity of species, which are able to grow under all types of extreme environments and exposed to a wide variety of predators and microbial pathogens. The antibacterial compounds described for these organisms include alkaloids, fatty acids, indoles, macrolides, peptides, phenols, pigments and terpenes, among others. This review presents an overview of antibacterial peptides isolated from cyanobacteria and microalgae, as well as their synergism and mechanisms of action described so far. Antibacterial cyanopeptides belong to different orders, but mainly from Oscillatoriales and Nostocales. Cyanopeptides have different structures but are mainly cyclic peptides. This vast peptide repertoire includes ribosomal and abundant non-ribosomal peptides, evaluated by standard conventional methodologies against pathogenic Gram-negative and Gram-positive bacteria. The antibacterial activity described for microalgal peptides is considerably scarcer, and limited to protein hydrolysates from two Chlorella species, and few peptides from Tetraselmis suecica. Despite the promising applications of antibacterial peptides and the importance of searching for new natural sources of antibiotics, limitations still persist for their pharmaceutical applications.

Profiling antimicrobial peptides from the medical maggot Lucilia sericata as potential antibiotics for MDR Gram-negative bacteria.

Background: The ability of MDR Gram-negative bacteria to evade even antibiotics of last resort is a severe global challenge. The development pipeline for conventional antibiotics cannot address this issue, but antimicrobial peptides (AMPs) offer an alternative solution. Objectives: Two insect-derived AMPs (LS-sarcotoxin and LS-stomoxyn) were profiled to assess their suitability for systemic application in humans. Methods: The peptides were tested against an extended panel of 114 clinical MDR Gram-negative bacterial isolates followed by time-kill analysis, interaction studies and assays to determine the likelihood of emerging resistance. In further in vitro studies we addressed cytotoxicity, cardiotoxicity and off-target interactions. In addition, an in vivo tolerability and pharmacokinetic study in mice was performed. Results: LS-sarcotoxin and LS-stomoxyn showed potent and selective activity against Gram-negative bacteria and no cross-resistance with carbapenems, fluoroquinolones or aminoglycosides. Peptide concentrations of 4 or 8 mg/L inhibited 90% of the clinical MDR isolates of Escherichia coli, Enterobacter cloacae, Acinetobacter baumannii and Salmonella enterica isolates tested. The 'all-d' homologues of the peptides displayed markedly reduced activity, indicating a chiral target. Pharmacological profiling revealed a good in vitro therapeutic index, no cytotoxicity or cardiotoxicity, an inconspicuous broad-panel off-target profile, and no acute toxicity in mice at 10 mg/kg. In mouse pharmacokinetic experiments LS-sarcotoxin and LS-stomoxyn plasma levels above the lower limit of quantification (1 and 0.25 mg/mL, respectively) were detected after 5 and 15 min, respectively. Conclusions: LS-sarcotoxin and LS-stomoxyn are suitable as lead candidates for the development of novel antibiotics; however, their pharmacokinetic properties need to be improved for systemic administration.

Identification and characterization of an antimicrobial peptide, lysozyme, from Suncus murinus.

Lysozyme is one of the most prominent antimicrobial peptides and has been identified from many mammalian species. However, this enzyme has not been studied in the order Insectivora, which includes the most primitive placental mammals. Here, we done the lysozyme cDNA from Suncus murinus (referred to as suncus, its laboratory name) and compare the predicted amino acid sequence to those from other mammalian species. Quantitative PCR analysis revealed a relatively higher expression of this gene in the spleen and gastrointestinal tract of suncus. The lysozyme-immunopositive (ip) cells were found mainly in the red pulp of the spleen and in the mucosa of the whole small intestine, including the follicle-associated epithelium and subepithelial dome of Peyer's patches. The lysozyme-ip cells in the small intestine were mostly distributed in the intestinal crypt, although lysozyme-expressing cells were found not only in the crypt but also in the villi. On the other hand, only a few lysozyme-ip cells were found in the villi and some granules showing intense fluorescence were located toward the lumen. As reported for other mammals, Ki67-ip cells were localized in the crypt and did not co-localize with the lysozyme-ip cells. Moreover, fasting induced a decrease in the mRNA levels of lysozyme in the intestine of suncus. In conclusion, we firstly identified the lysozyme mRNA sequence, clarified expression profile of lysozyme transcripts in suncus and found a unique distribution of lysozyme-producing cells in the suncus intestine.

The defensive system of tree frog skin identified by peptidomics and RNA sequencing analysis.

The diversity of defensive peptides from skin of amphibians has been demonstrated. These peptides may have resulted from the diversity of microorganisms encountered by amphibians. In this study, peptidomics and RNA sequencing analyses were used to study deeply the defensive peptides of the skin secretions from Polypedates megacephalus. A total of 99 defensive peptides have been identified from the skin secretions. Among these peptides, 3 peptides were myotropical peptides and 34 peptides classified as protease inhibitor peptides. 5 lectins, 8 antimicrobial peptides, 26 immunomodulatory peptides, 10 wound-healing peptides and 13 other bioactive peptides were identified as belonging to the innate immune system. One antimicrobial peptide Pm-amp1 showed high similarity to antimicrobial peptide marcin-18. This peptide was successfully expressed and showed moderate activity against four tested strains. These identified peptides highlight the extensive diversity of defensive peptides and provide powerful tools to understand the defense weapon of frog.