Two families of antimicrobial peptides with multiple functions from skin of rufous-spotted torrent frog, Amolops loloensis

Molecular Cloning and Characterization of a Novel Antimicrobial Peptide from the Skin of Kaloula pulchra

BACKGROUND

Bacterial resistance to all currently available conventional antibiotics has caused a global public health crisis and led to an imperative search for new agents. Antimicrobial peptides (AMPs) are essential components of host innate immune defense against microbial invasions.

OBJECTIVES

The objective of this study was to report a novel AMP, brevinin-2KP, from the skin of the black Kaloula pulchra frog and describe its structural and biological characterization.

MATERIALS AND METHODS

The physical and chemical parameters of brevinin-2KP were predicted with the ExPASy Bioinformatics Resource Portal. The assembled sequences were aligned with ClustalW, and the phylogenetic tree was constructed using Mega. Circular dichroism (CD) experiments were carried out to identify the secondary structure and the stability of peptide in different solvent environments. The cytotoxicity of brevinin-2KP was evaluated by the MTT test. To determine antibacterial activity of brevinin- 2KP, a standard two-fold broth dilution method was used. SEM was carried out to observe the morphological change in the bacterial treated by brevinin-2KP. The live/dead bacterial viability was measured with a LIVE/DEAD® BacLight kit. Histamine release and mast cell degranulation assays were performed.

RESULTS

The precursor of brevinin-2KP contains 72 amino acid residues, including a conserved signal peptide, acidic propeptide with KR residues, and mature peptide with a sequence of GVITDALKGAAKTVAAELLKKAHCKLTNSC. Phylogenetic analysis based on the amino acid sequences of 34 brevinin-2 peptides from 30 anuran species demonstrates that K. pulchra is genetically closely related to the genus Hylarana. The CD spectra analysis indicates that brevinin-2KP adopts random coil in the water and an organized α-helical conformation in SDS solution. Further, this secondary structure is stable under high salt and high-temperature conditions. Brevinin-2KP is weakly active towards the tested Gram-positive and Gram-negative bacteria as well as fungi due to its membranolytic action. Moreover, brevinin-2KP inhibits the proliferation of several mammal cells with IC₅₀ values ranging from 3.27 to 59.75 μM. In addition, brevinin-2KP promotes degranulation and histamine release of mast cells, indicating that it is involved in the inflammatory response.

CONCLUSION

This is the first report on AMP identified from the skin of K. pulchra. Brevinin-2KP adopts a typical amphipathic α-helix conformation in membrane mimic environment and shows antimicrobial and antitumor activities by potential membranolytic mechanism. In addition, brevinin-2KP can promote degranulation and histamine release of mast cells. Brevinin-2KP is expected to become a good drug temple molecule.

Evaluation of the Antimicrobial Properties of a Natural Peptide from Vespa mandarinia Venom and Its Synthetic Analogues as a Possible Route to Defeat Drug-Resistant Microbes

Antimicrobial peptides (AMPs) from wasp venom have a good track record and potential for drug development as tools against development of antimicrobial resistance. Herein, the biological function and activity profile of peptide VM, which was discovered in the venom of the wasp, Vespamandarinia, and several of its third-position substituted analogues, were investigated. VM had potent antimicrobial activity against Gram-positive bacteria and biofilm, and all modified peptides achieved the significant enhancement of these capacities. The various physicochemical properties of amino acids substituted in analogues, generated the different mechanisms of action of bacterial membrane disruption. VM-3K showed a maximum 8-fold enhancement of antibacterial activity against Gram-positive bacteria and also presented microbicidal properties against Gram-negative bacteria and fungi. This peptide also exhibited a high killing efficiency at low concentration and had a comparable selectivity index to VM. Furthermore, VM-3K produced a 90% survival of S. aureus-infected waxworms at a concentration of 5.656 mg/kg, at which concentration the natural template peptide only achieved 50% survival. This peptide also lacked short-term resistance generation. Thus, peptide VM-3K could be a promising broad-spectrum antimicrobial candidate for addressing the current antibiotic-resistant infection crisis. It is worth mentioning that this investigation on the relationship between peptide structure and mechanism of action could become an important aspect of drug research on short peptides.

Discovery of Antioxidant Peptides from Amphibians: A Review

In recent years, bioactive peptide drugs have attracted growing attention due to the increasing difficulty in developing new drugs with novel chemical structures. In addition, many diseases are linked to excessive oxidation in the human body. Therefore, the role of peptides with antioxidant activity in counteracting diseases related to oxidative stress is worth exploring. Amphibians are a major repository for bioactive peptides that protect the skin from biotic and abiotic stresses, such as microbial infection and radiation injury. We characterized the first amphibian- derived gene-encoded antioxidant peptides in 2008. Since then, a variety of antioxidant peptides have been detected in different amphibian species. In this work, the physicochemical properties of antioxidant peptides identified from amphibians are reviewed for the first time, particularly acquisition methods, amino acid characteristics, antioxidant mechanisms, and application prospects. This review should provide a reference for advancing the identification, structural analysis, and potential therapeutic value of natural antioxidant peptides.

Antiviral activity and mechanism of ESC-1GN from skin secretion of hylarana guentheri against influenza a virus

Development of new and effective anti-influenza drugs is critical for prophylaxis and treatment of influenza A virus infection. A wide range of amphibian skin secretions have been identified to show antiviral activity. Our previously reported ESC-1GN, a peptide from the skin secretion of Hylarana guentheri, displayed good antimicrobial and anti-inflammatory effects. Here, we found that ESC-1GN possessed significant antiviral effects against influenza A viruses. Moreover, ESC-1GN could inhibit the entry of divergent H5N1 and H1N1 virus strains with the IC50 values from 1.29 to 4.59 μM. Mechanism studies demonstrated that ESC-1GN disrupted membrane fusion activity of influenza A viruses by interaction with HA2 subunit. The results of site-directed mutant assay and molecular docking revealed that E105, N50 and the residues around them on HA2 subunit could form hydrogen bonds with amino acid on ESC-1GN, which were critical for ESC-1GN binding to HA2 and inhibiting the entry of influenza A viruses. Altogether, these not only suggest that ESC-1GN maybe represent a new type of excellent template designing drugs against influenza A viruses, but also it may shed light on the immune mechanism and survival strategy of H. guentheri against viral pathogens.

Antimicrobial Peptides: Amphibian Host Defense Peptides

Antimicrobial Peptides (AMPs) are one of the most common components of the innate immune system that protect multicellular organisms against microbial invasion. The vast majority of AMPs are isolated from the frog skin. Anuran (frogs and toads) skin contains abundant AMPs that can be developed therapeutically. Such peptides are a unique but diverse group of molecules. In general, more than 50% of the amino acid residues form the hydrophobic part of the molecule. Normally, there are no conserved structural motifs responsible for activity, although the vast majority of the AMPs are cationic due to the presence of multiple lysine residues; this cationicity has a close relationship with antibacterial activity. Notably, recent evidence suggests that synthesis of AMPs in frog skin may confer an advantage on a particular species, although they are not essential for survival. Frog skin AMPs exert potent activity against antibiotic-resistant bacteria, protozoa, yeasts, and fungi by permeating and destroying the plasma membrane and inactivating intracellular targets. Importantly, since they do not bind to a specific receptor, AMPs are less likely to induce resistance mechanisms. Currently, the best known amphibian AMPs are esculentins, brevinins, ranacyclins, ranatuerins, nigrocin-2, magainins, dermaseptins, bombinins, temporins, and japonicins-1 and -2, and palustrin-2. This review focuses on these frog skin AMPs and the mechanisms underlying their antimicrobial activity. We hope that this review will provide further information that will facilitate further study of AMPs and cast new light on novel and safer microbicides.

Temporins: An Approach of Potential Pharmaceutic Candidates

Antimicrobial peptides (AMPs), also known as host defense peptides, are small and mostly polycationic molecules that form part of the innate immune response. There are currently more than 3000 experimentally reported AMPs. Particularly in frogs, the temporin family has been discovered as potential AMPs. The aim of this work is to review the latest publications about this class of peptides, discuss their properties, and present an update of the last studies and new discoveries in the field. More than 130 temporins have been identified in this family. The most studied temporins are temporin A (TA), temporin B (TB), and temporin L (TL). These peptides showed antimicrobial activity against gram-negative, gram-positive bacteria and fungi. Since the discovery of temporins in 1996, several groups of researchers isolated different peptides from various species of frogs that were included as members of this family. Although antimicrobial activity of many temporins has not been analyzed yet, most of them showed antimicrobial and antifungal activities. A combination of nanotechnology and AMPs for temporins in different antimicrobial treatments could be a promising alternative for resistant pathogens. These studies demonstrate that, even with the advancement in scientific research on the composition and antimicrobial activity of temporins, further studies are necessary to wholly understand their components and mechanisms of action.

Antimicrobial Peptides as Anti-Infective Agents in Pre-Post-Antibiotic Era?

Resistance to antibiotics is one of the main current threats to human health and every year multi-drug resistant bacteria are infecting millions of people worldwide, with many dying as a result. Ever since their discovery, some 40 years ago, the antimicrobial peptides (AMPs) of innate defense have been hailed as a potential alternative to conventional antibiotics due to their relatively low potential to elicit resistance. Despite continued effort by both academia and start-ups, currently there are still no antibiotics based on AMPs in use. In this study, we discuss what we know and what we do not know about these agents, and what we need to know to successfully translate discovery to application. Understanding the complex mechanics of action of these peptides is the main prerequisite for identifying and/or designing or redesigning novel molecules with potent biological activity. However, other aspects also need to be well elucidated, i.e., the (bio)synthetic processes, physiological and pathological contexts of their activity, and a quantitative understanding of how physico-chemical properties affect activity. Research groups worldwide are using biological, biophysical, and algorithmic techniques to develop models aimed at designing molecules with the necessary blend of antimicrobial potency and low toxicity. Shedding light on some open questions may contribute toward improving this process.

Host Defense Peptides from Asian Frogs as Potential Clinical Therapies

Host defense peptides (HDPs) are currently major focal points of medical research as infectious microbes are gaining resistance to existing drugs. They are effective against multi-drug resistant pathogens due to their unique primary target, biological membranes, and their peculiar mode of action. Even though HDPs from 60 Asian frog species belonging to 15 genera have been characterized, research into these peptides is at a very early stage. The purpose of this review is to showcase the status of peptide research in Asia. Here we provide a summary of HDPs from Asian frogs.

The diversity and evolution of anuran skin peptides

Amphibians exhibit various, characteristic adaptations related to their "incomplete" shift from the aquatic to the terrestrial habitat. In particular, the integument was subject to a number of specialized modifications during the evolution of these animals. In this review, we place special emphasis on endogenous host-defence skin peptides from the cuteanous granular glands anuran amphibians (frogs and toads). The overview on the two broad groups of neuroactive and antimicrobial peptides (AMPs) goes beyond a simple itemization in that we provide a new perspective into the evolution and function of anuran AMPs. Briefly, these cationic, amphipathic and α-helical peptides are traditionally viewed as being part of the innate immune system, protecting the moist skin against invading microorganisms through their cytolytic action. However, the complete record of anuran species investigated to date suggests that AMPs are distributed sporadically (i.e., non-universally) across Anura. Together with the intriguing observation that virtually all anurans known to produce neuropeptides in their granular glands also co-secrete cytolytic peptides, we call the traditional role for AMPs as being purely antimicrobial into question and present an alternative scenario. We hypothesize AMPs to assist neuroactive peptides in their antipredator role through their cytolytic action increasing the delivery of the latter to the endocrine and nervous system of the predator. Thus, AMPs are more accurately viewed as cytolysins and their contribution to the immune system is better regarded as an accessory benefit.

A Novel Insulinotropic Peptide from the Skin Secretions of Amolops loloensis Frog

Various kinds of biologically active peptides have previously been isolated from the skin secretions of Amolops loloensis frog, such as antimicrobial peptides, bradykinin-like peptides and algesic peptides. A novel insulinotropic peptide named amolopin was identified in A. loloensis frog's skin secretion. Its primary structure sequence was determined by Edman degradation as: FLPIVGKSLSGLSGKL-NH2. BLAST search indicates that the amino acid sequence of amolopin is quite different from other known insulin secretagogues, including mastoparan, exendins and α-latrotoxin, nor does it like incretins (e.g. glucagons like peptide-1 and glucose-dependent insulinotropic ploypeptide) either. However, amolopin shows certain structural similarity with amphibian antimicrobial temporins and vespid chemotactic peptides isolated from Vespa magnifica. Amolopin can stimulate insulin release in INS-1 cells in a dose-dependent manner. Primary investigation on its action mechanisms reveals that amolopin does not increase the influx of Ca(2+). In conclusion, a novel 16-amino acid peptide with insulin-releasing activity is initially discovered from the skin secretion of A. loloensis frog. Further work is necessary to evaluate its potential as novel anti-diabetic candidate.

Peptidomic analysis of antimicrobial peptides in skin secretions of Amolops mantzorum

Amphibian skin secretions contain abundant bioactive peptides that are valuable natural resources for human beings. However, many amphibians are disappearing from the world, making relevant scientific studies even more important. In this study, 24 cDNA sequences encoding antimicrobial peptide (AMP) precursors were initially cloned by screening a cDNA library derived from the skin of the Sichuan torrent frog, Amolops mantzorum. Eighteen mature AMPs belonging to 11 different families were deduced from these cDNA clones. Biological function was confirmed in each family of these AMPs. Some of them were purified from the skin secretions, and their molecular structures were determined by Edman degradation. Liquid chromatography in conjunction with tandem mass spectrometry (LC-MS/MS)-based peptidomics was used to further confirm the actual presence and characteristics of mature AMPs in the skin secretions of A. mantzorum. Incomplete tryptic digestion and gas-phase fractionation (GPF) analysis were used to increase the peptidome coverage and reproducibility of peptide ion selection.

Anticancer mechanisms of temporin-1CEa, an amphipathic α-helical antimicrobial peptide, in Bcap-37 human breast cancer cells

AIMS

Temporin-1CEa, a 17-residue antimicrobial peptide, is known to exert broad-spectrum anticancer activity that acts preferentially on cancer cells instead of normal cells. However, the mechanism of cancer cell death induced by temporin-1CEa is weakly understood.

MAIN METHODS

Here, we investigated the cytotoxic and membrane-disrupting effects of temporin-1CEa on human breast cancer cell line Bcap-37, using MTT assay, electronic microscope observation, fluorescence imaging and flow cytometry analysis.

KEY FINDINGS

The MTT assay indicated that one-hour temporin-1CEa treatment led to rapid cell death in either caspase-dependent or -independent manner. The electronic microscope observation suggested that temporin-1CEa exposure resulted in profound morphological changes in Bcap-37 cells. The fluorescence imaging and flow cytometry analysis demonstrated that temporin-1CEa exhibited membrane-disrupting property characterized by induction of cell-surface phosphatidylserine exposure, elevation of plasma membrane permeability, and rapid transmembrane potential depolarization. Moreover, temporin-1CEa might also induce rapid cell death through mitochondria-involved mechanisms, including rapid intracellular Ca(2+) leakage, collapse of mitochondrial membrane potential (Δφm) and over-generation of reactive oxygen species (ROS).

SIGNIFICANCE

In summary, the present study indicates that temporin-1CEa triggers a rapid cytotoxicity in Bcap-37 cells through membrane-destruction and intracellular mechanisms involving mitochondria. These intracellular mechanisms and direct membrane-destruction effect were evaluated helping to understand the detail action of antimicrobial peptides in mammalian cancer cells.

Characterization of diverse antimicrobial peptides in skin secretions of Chungan torrent frog Amolops chunganensis

We have cloned, synthesized, and characterized 11 novel antimicrobial peptides from a skin derived cDNA library of the Chungan torrent frog, Amolops chunganensis. Seven of the 11 antimicrobial peptides were present in authentic A. chunganensis skin secretions. Sequence analysis indicated that the 11 peptides belonged to the temporin, esculentin-2, palustrin-2, brevinin-1, and brevinin-2 families. The peptides displayed potent antimicrobial activities against several strains of microorganisms. One peptide, brevinin-1CG5, demonstrated antimicrobial activity against all tested Gram-positive and Gram-negative bacteria and fungi, and showed high antimicrobial potency (MIC=0.6 μM) against Gram-positive bacterium Rhodococcus rhodochrous. Some peptides also demonstrated weak hemolytic activity against human erythrocytes in vitro. Phylogenetic analysis based on the amino acid sequences of brevinin-1, brevinin-2, and esculentin-2 peptides from family Ranidae confirmed that the current taxonomic status of A. chunganensis is correct.

Hainanenins: a novel family of antimicrobial peptides with strong activity from Hainan cascade-frog, Amolops hainanensis

Antimicrobial peptides (AMPs) secreted by amphibian skin represent an important innate immune defense strategy. There are more than 340 species in the family of Ranidae worldwidely, and from which nearly 100 families of AMPs comprising between 8 and 48 amino acid (aa) residues have been characterized. In current work, two novel AMPs were purified from the skin secretion of Hainan cascade-frog, Amolops hainanensis, and 31 cDNA sequences encoding 10 novel AMPs belonging to 4 families were cloned from the constructed skin cDNA library of A. hainanensis. Among these 10 AMPs, 5 peptides represent the prototypes of a novel amphibian AMP family. According to the generic name of the species of origin, they were designated as hainanenin-1-5. Each of them consists of 21 aa residues with a C-terminal disulphide loop of 7 residues between Cys(15) and Cys(21). Two of them (hainanenin-1 and 5) were then synthesized and their in vitro activities were screened, including antimicrobial, hemolytic and antioxidant activities. The results showed that hainanenin-1 and 5 possessed strong and broad-spectrum antimicrobial activities against Gram-positive, Gram-negative bacteria and fungi, including a large number of clinically isolated drug-resistant pathogenic microorganisms, and slight antioxidant activity. Undesirably, hainanenin-1 and 5 exhibited strong hemolytic activity on human erythrocytes. The discovery of hainanenins and their great antimicrobial potency provides new templates for anti-infective agent design.

Identification and characterization of antimicrobial peptides from skin of Amolops ricketti (Anura: Ranidae)

As one of large amphibian group, there are a total of 45 species of Amolops in the world. However, the antimicrobial peptides (AMPs) existing in this genus has not been extensively studied. In this study, cDNAs encoding five novel AMP precursors were cloned by screening the skin-derived cDNA library of Amolops ricketti, a frog species that exists in southern and western parts of China. Protein sequence analysis led to the identification of five deduced peptides, three belonging to the brevinin-1 family and two belonging to the brevinin-2 family of amphibian AMPs. Thus, they were named as brevinin-1RTa (FLPLLAGVVANFLPQIICKIARKC), brevinin-1RTb (FLGSLLGLVGKVVPTLFCKISKKC), brevinin-1RTc (FLGSLLGLVGKIVPTLICKISKKC), brevinin-2RTa (GLMSTLKDFGKTAAKEIAQSLLSTASCKLAKTC), and brevinin-2RTb (GILDTLKEFGKTAAKGIAQSLLSTASCKLAKTC), respectively. The purification of brevinin-1RTa, brevinin-1RTb, and brevinin-2RTb was carried out by RP-HPLC, and confirmed by the LC-MS/MS-based proteomics approach. All of the peptides displayed different antimicrobial potency against a variety of microorganisms. In addition, brevinin-2RTa and brevinin-2RTb were found to have relatively low hemolytic activity (>400μg/ml) against mammalian red blood cells in vitro, which could potentially be as candidates for developing novel anti-infection agents.

The cathelicidin-like peptide derived from panda genome is a potential antimicrobial peptide

A novel cathelicidin-like antimicrobial peptide was identified by mining genome of panda. This peptide (cathelicidin-AM) was synthesized. It showed potential antimicrobial activities against wide spectrum of microorganisms including Gram-negative and -positive bacteria, and fungi. It had similar antimicrobial abilities against both standard and clinically isolated drug-resistant strains. Cathelicidin-AM could rapidly exert its antibacterial activities. It just took less than 1h to kill all Staphylococcus sciuri at the concentration of 2, 4 or 10 times of minimal inhibitory concentration (MIC) while clindamycin took 6h. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis indicated that cathelicidin-AM killed bacteria by directly affecting bacterial cell wall and membrane. Phylogenetic analysis revealed that the panda cathelicidin had the nearest evolution relationship with dog cathelicidin. The current work provides a novel cathelicidin-like peptide with strong antimicrobial abilities.

Short native antimicrobial peptides and engineered ultrashort lipopeptides: similarities and differences in cell specificities and modes of action

Due to the rapid emergence of resistant microbes to the currently available antibiotics, cationic antimicrobial peptides have attracted considerable interest as a possible new generation of anti-infective compounds. However, low cost development for therapeutic or industrial purposes requires, among other properties, that the peptides will be small and with simple structure. Therefore, considerable research has been devoted to optimizing peptide length combined with a simple design. This review focuses on the similarities and differences in the mode of action and target cell specificity of two families of small peptides: the naturally occurring temporins from the skin of amphibia and the engineered ultrashort lipopeptides. We will also discuss the finding that acylation of cationic peptides results in molecules with a more potent spectrum of activity and a higher resistance to proteolytic degradation. Conjugation of fatty acids to linear native peptide sequences is a powerful strategy to engineer novel successful anti-infective drugs.

A novel antimicrobial peptide from skin secretions of the earthworm, Pheretima guillelmi (Michaelsen)

A novel lumbricin-like antimicrobial peptide named lumbricin-PG was isolated from skin secretions of the earthworm, Pheretima guillelmi (Michaelsen), using a procedure of one step Sephadex G-50 gel filtration and one step C(8) reverse-phase high-performance liquid chromatography (RP-HPLC). Its amino acid sequence was determined as FSRYARMRDSRPWSDRKNNYSGPQFTYPPEKAPPEKLIKWNN EGSPIFEMPAEGGHIEP by Edman degradation combined with cDNA cloning and mass spectrometry analysis. The cDNA encoding lumbricin-PG was cloned by cDNA library screening. The predicted protein from the cDNA sequence was composed of 73 amino acid residues including a mature lumbricin-PG and predicted signal peptide. It showed similarity with lumbricin antimicrobial peptide from the earthworm, Lumbricus rubellus by BLAST search. Purified lumbricin-PG exerted potential antimicrobial activities against bacteria and fungi; it showed weak hemolysis activity against human and rabbit red cells.

A defensin-like antimicrobial peptide from the venoms of spider, Ornithoctonus hainana

The defensin-like antimicrobial peptides have been characterized from various other arthropods including insects, scorpions, and ticks. But no natural spider defensin-like antimicrobial peptides have ever been isolated from spiders, except couple of cDNA and DNA sequences of five spider species revealed by previous genomic study. In this work, a defensin-like antimicrobial peptide named Oh-defensin was purified and characterized from the venoms of the spider, Ornithoctonus hainana. Oh-defensin is composed of 52 amino acid (aa) residues including six Cys residues that possibly form three disulfide bridges. Its aa sequence is MLCKLSMFGAVLGV PACAIDCLPMGKTGGSCEGGVCGCRKLTFKILWDKKFG. By BLAST search, Oh-defensin showed significant sequence similarity to other arthropod antimicrobial peptides of the defensin family. Oh-defensin exerted potent antimicrobial activities against tested microorganisms including Gram-positive bacteria, Gram-negative bacteria, and fungi. The cDNA encoding Oh-defensin precursor was also cloned from the cDNA library of O. hainana.

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.

Novel family of antimicrobial peptides from the skin of Rana shuchinae

So far numerous antimicrobial peptides have been characterized from amphibians. In this work, a new family of antimicrobial peptides, named shuchin, was purified and characterized from skin secretions of the frog, Rana shuchinae that lives in freezing mountains. Totally two members of shuchin (shuchin 1 and 2) were identified with the amino acid sequence of NALSMPRNKCNRALMCFG and NALSSPRNKCDRASSCFG, respectively. cDNAs encoding shuchins were cloned from the skin cDNA library of R. shuchinae. The precursors of shuchin are composed of 62 amino acid residues including the conserved signal peptides, acidic propieces, and mature antimicrobial peptides. Synthetic shuchins showed strong and broad antimicrobial activities against Gram-positive bacteria (Staphylococcus aureus, and Bacillus cereus; MICs<12.5 microg/ml), Gram-negative bacteria (Escherichia coli, Bacillus dysenteriae, Pseudomonas aeruginosa; most MICs from 3.1 to 12.5 microg/ml), and yeast (Candida albicans; MICs of 6.25 microg/ml), but no hemolytic activity under the effective concentration, thereby provide more leading templates for designing novel anti-infection agents.

[Animal toxins and human disease: from single component to venomics, from biochemical characterization to disease mechanisms, from crude venom utilization to rational drug design]

Many animals produced a diversity of venoms and secretions to adapt the changes of environments through the long history of evolution. The components including a large quantity of specific and highly active peptides and proteins have become good research models for protein structure-function and also served as tools and novel clues for illustration of human disease mechanisms. At the same time, they are rich natural resources for new drug development. Through the valuable venomous animal resources of China, researchers at the Kunming Institute of Zoology, CAS have carried out animal toxin research over 30 years. This paper reviews the main work conducted on snake venoms, amphibian and insect secretions, and the development from single component to venomics, from biochemical characterization to human disease mechanisms, from crude venom to rational drug design along with a short perspective on future studies.

Combined peptidomics and genomics approach to the isolation of amphibian antimicrobial peptides

A large number of diverse antimicrobial peptides have been found in amphibian skins, and many more remain to be identified. It is sufficiently easy to obtain amounts of gland secretions sufficient for both identification and functional testing of the bioactive peptides. We describe here a systematic peptidomics approach which we combined with genomics and functional testing. This has proven to be an effective way to identify amphibian antimicrobial peptides, including novel peptide families. Protocols are exemplified for Bombina maxima and Odorrana grahami and can be easily adapted for use with other amphibian species.

Synergistic antibacterial and anti-inflammatory activity of temporin A and modified temporin B in vivo

Temporins are antimicrobial peptides secreted by the granular glands of the European red frog (Rana temporaria). They are 10–14 amino acid long polypeptides active prevalently against gram positive bacteria. This study shows that a synthetic temporin B analogue (TB-YK), acquires the capacity to act in synergism with temporin A and to exert antimicrobial and anti-inflammatory activity in vivo against gram positive and gram negative bacteria. Administration of 3.4 mg/Kg of temporin A (TA)+1.6 mg/Kg TB-YK, given to individual mice concurrently with a lethal dose of bacteria (gram positive or negative), rescued 100% of the animals. More importantly, the same doses of temporins, administered one week after experimental infection with a sub lethal dose of bacteria, sterilized 100% of the animals within 3–6 days. Also, it is described an animal model based on the use of sub lethal doses of bacteria, which closely mimics bacterial infection in humans. The model offers the possibility to test in a preclinical setting the true potential of TA and TB-YK in combination as antimicrobial and anti-inflammatory agents.

Purification, characterization and cloning of two novel tigerinin-like peptides from skin secretions of Fejervarya cancrivora

While investigating the innate defense of brackish water-living amphibian and its comparison with freshwater-living amphibians, two novel 12-residue antimicrobial peptides were purified from the skin secretions of the crab-eating frog, Fejervarya cancrivora which typically inhabits brackish water of mangrove forests of Southeast Asia. These two antimicrobial peptides, tigerinin-RC1 and -RC2 share significant structural similarity with tigerinins found in the skin of Indian frog, Hoplobatrachus tigerinus. cDNAs encoding tigerinin-RC1 and -RC2 were also cloned from the skin cDNA library of F. cancrivora. Tigerinin-RC precursors are composed of 71 amino acid residues including a signal peptide, acidic spacer peptide, which are very similar to other amphibian antimicrobial peptide precursors and mature tigerinin-RC. The current results confirmed that both amphibians inhabiting freshwater and brackish water share the same antimicrobial peptide family to exert innate defense. Furthermore, the current work was also the first report of precursor and cDNA cloning of the tigerinin antimicrobial peptide family.

The novel antimicrobial peptides from skin of Chinese broad-folded frog, Hylarana latouchii (Anura:Ranidae)

Broad-folded frogs (Hylarana latouchii), one member of 12 species of the genus Hylarana in the Chinese frog fauna, are widely distributed in the South of China. In this study, we purified and characterized three antimicrobial peptides from the skin secretion of H. latouchii. Five different cDNA fragments encoding the precursors of these antimicrobial peptides were cloned, and five mature antimicrobial peptides belonging to two different families were deduced from the five cDNAs. Structural characterization of the mature peptides had identified them as members of the brevinin-1 and temporin families. They were named brevinin-1LTa (FFGTALKIAANVLPTAICKILKKC), brevinin-1LTb (FFGTALKIAANILPTAICKILKKC), temporin-LTa (FFPLVLGALGSILPKIF-NH(2)), temporin-LTb (FIITGLVRGLTKLF-NH(2)) and temorin-LTc (SLSRFLSFLKIVYPPAF-NH(2)). Brevinin-1LTa, temporin-LTa, temporin-LTb and temporin-LTc with different antimicrobial activities induced significant morphological alterations of the tested microbial surfaces as shown by scanning electron microscopy, which indicated strong membrane disruption.

Antioxidant peptidomics reveals novel skin antioxidant system

It is generally agreed that reactive oxygen species (ROS) contribute to skin aging, skin disorders, and skin diseases. Skin possesses an extremely efficient antioxidant system. This antioxidant activity is conferred by two systems: antioxidant enzymes and small molecules that can scavenge ROS by donating electrons. No gene-encoded secreted ROS scavengers have been reported. Amphibian skin is a multifunctional organ acting in defense, respiration, and water regulation, although it seems susceptible. Amphibian skins are easily harmed by biological or non-biological attacks such as microorganism infection or radiation injury. Among vertebrates, skins of amphibian are exposed to more dangers of radiation injury than others. Radiation toxicity occurs by directly attacking the genetic material and/or by generating ROS. In addition, amphibian skin respiration and inflammatory response also induce ROS generation. It is rational to hypothesize that amphibian skins should have potent free radical scavenging and radioprotective ability for their survival. Rana pleuraden is distributed in Southwest of China; it lives in the subtropical plateau (altitude around 2300 m) where there is strong ultraviolet radiation and long duration of sunshine. By peptidomics and genomics approaches, a large amount of antioxidant peptides belonging to 11 different groups with variable structures were isolated from the skin secretions of R. pleuraden. Their free radical scavenging and anti-inflammatory abilities were studied. All of these peptide share highly homologous preproregions, although mature antioxidant peptides have very divergent primary structures, suggesting the possibility of a common ancestor. Some peptides were also found to have multifunctional properties, such as combined antioxidant, anti-inflammatory, and antimicrobial activities. According to our knowledge, no gene-encoded specific antioxidant peptides have been reported except metallothionein. Our work possibly reveals a new skin antioxidant system. The current work also provides a large amount of peptide candidates with medical-pharmaceutical significance.

A novel serine protease inhibitor from Bungarus fasciatus venom

By Sephadex G-50 gel filtration, cation-exchange CM-Sephadex C-25 chromatography and reversed phase high-performance liquid chromatography (HPLC), a novel serine protease inhibitor named bungaruskunin was purified and characterized from venom of Bungarus fasciatus. Its cDNA was also cloned from the cDNA library of B. fasciatus venomous glands. The predicted precursor is composed of 83 amino acid (aa) residues including a 24-aa signal peptide and a 59-aa mature bungaruskunin. Bungaruskunin showed maximal similarity (64%) with the predicted serine protease inhibitor blackelin deduced from the cDNA sequence of the red-bellied black snake Pseudechis porphyriacus. Bungaruskunin is a Kunitz protease inhibitor with a conserved Kunitz domain and could exert inhibitory activity against trypsin, chymotrypsin, and elastase. By screening the cDNA library, two new B chains of beta-bungarotoxin are also identified. The overall structures of bungaruskunin and beta-bungarotoxin B chains are similar; especially they have highly conserved signal peptide sequences. These findings strongly suggest that snake Kunitz/BPTI protease inhibitors and neurotoxic homologs may have originated from a common ancestor.

Two serine protease inhibitors from the skin secretions of the toad, Bombina microdeladigitora

Two serine protease inhibitors (named BMSI 1 and BMSI 2, respectively) were identified from the skin secretions of the toad, Bombina microdeladigitora. The cDNAs encoding BMSIs were cloned from a cDNA library prepared from the toad skin. The deduced complete amino acid sequences of BMSIs indicate that mature BMSI 1 and BMSI 2 are composed of 60 amino acids including 10 half-cystines to form 5 disulfide bridges. A FASTA search in the databanks revealed that BMSIs exhibit sequence similarity with other serine protease inhibitors from amphibians of the genus Bombina. BMSI 1 potently inhibited trypsin and thrombin with a K(i) value of 0.02 microM and 0.15 microM, respectively. Sequence analysis revealed that all serine protease inhibitors from five amphibians of the genus Bombina share highly conserved primary structures.

Biological characterization and modes of action of temporins and bombinins H, multiple forms of short and mildly cationic anti-microbial peptides from amphibian skin

Genetically encoded cationic anti-microbial peptides (AMPs) are essential components of the ancient and non-specific innate immune system, which is the principal defence mechanism of all species of life, with the primary role to kill infectious microorganisms. Amphibian skin is one of the richest natural sources of such molecules, which are produced by holocrine-type dermal glands and released upon stimulation. This review highlights the attractive and unique structural/functional properties of temporins and bombinins H, two families of short and mildly cationic peptides, isolated from the skin of frogs belonging to Rana and Bombina genera, respectively. Beside improving our knowledge on the role of AMPs in the regulation of the innate immunity, the biological significance of the existence of multiple forms of a prototypic peptide sequence within the same organism and the implication of short peptides in the endotoxin neutralization, these two classes of AMPs can be also considered as valid candidates for the design of novel anti-infective and anti-sepsis drugs.