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

Characterization of a novel LTA/LPS-binding antimicrobial and anti-inflammatory temporin peptide from the skin of Fejervary limnocharis (Anura: Ranidae)

Septic shock caused by Gram-positive bacteria continues to be a major cause of morbidity and mortality in intensive care units globally. Most Temporins are excellent growth inhibitors of gram-positive bacteria and candidates for developing antimicrobial treatments due to their biological action and small molecular weight. In this study, a novel Temporin peptide from the skin of Fejervarya limnocharis frog, named as Temporin-FL, was characterized. Temporin-FL was found to adopt typical α-helical conformation in SDS solution and to exhibit selective antibacterial activity against Gram-positive bacteria through a membrane destruction mechanism. Accordingly, Temporin-FL showed protective effects against Staphylococcus aureus-induced sepsis in mice. Finally, Temporin-FL was demonstrated to exert anti-inflammatory effects by neutralizing the action of LPS/LTA and by inhibiting MAPK pathway activation. Therefore, Temporin-FL represents a novel candidate for moleculartherapy of Gram-positive bacterial sepsis.

Discovery of a Novel Antimicrobial Peptide, Temporin-PKE, from the Skin Secretion of Pelophylax kl. esculentus, and Evaluation of Its Structure-Activity Relationships

Bacterial resistance against antibiotics has led to increasing numbers of treatment failures, and AMPs are widely accepted as becoming potential alternatives due to their advantages. Temporin-PKE is a novel peptide extracted from the skin secretion of Pelophylax kl. esculentus and it displays a strong activity against Gram-positive bacteria, with an extreme cytotoxicity. Incorporating positively charged residues and introducing D-amino acids were the two main strategies adopted for the modifications. The transformation of the chirality of Ile could reduce haemolytic activity, and an analogue with appropriate D-isoforms could maintain antimicrobial activity and stability. The substitution of hydrophobic residues could bring about more potent and broad-spectrum antimicrobial activities. The analogues with Lys were less harmful to the normal cells and their stabilities remained at similarly high levels compared to temporin-PKE. The optimal number of charges was three, and the replacement on the polar face was a better choice. Temporin-PKE-3K exerted dually efficient functions includingstrong antimicrobial and anticancer activity. This analogue showed a reduced possibility for inducing resistance in MRSA and Klebsiella pneumoniae, a rather strong antimicrobial activity in vivo, and it exhibited the highest therapeutic index such that temporin-PKE-3K has the potential to be developed as a clinical drug.

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.

Enhanced Antimicrobial Activity of N-Terminal Derivatives of a Novel Brevinin-1 Peptide from The Skin Secretion of Odorrana schmackeri

Antimicrobial peptides (AMPs) are promising therapeutic alternatives compared to conventional antibiotics for the treatment of drug-resistant bacterial infections. However, the application of the overwhelming majority of AMPs is limited because of the high toxicity and high manufacturing costs. Amphibian skin secretion has been proven to be a promising source for the discovery and development of novel AMPs. Herein, we discovered a novel AMP from the skin secretion of Odorrana schmackeri, and designed the analogues by altering the key factors, including conformation, net charge and amphipathicity, to generate short AMPs with enhanced therapeutic efficacy. All the peptides were chemically synthesised, followed by evaluating their biological activity, stability and cytotoxicity. OSd, OSe and OSf exhibited broad-spectrum antibacterial effects, especially OSf, which presented the highest therapeutic index for the tested bacteria. Moreover, these peptides displayed good stability. The results from scanning electron microscopy and transmission electron microscopy studies, indicated that brevinin-OS, OSd, OSe and OSf possessed rapid bactericidal ability by disturbing membrane permeability and causing the release of cytoplasmic contents. In addition, OSd, OSe and OSf dramatically decreased the mortality of waxworms acutely infected with MRSA. Taken together, these data suggested that a balance between positive charge, degrees of α-helicity and hydrophobicity, is necessary for maintaining antimicrobial activity, and these data successfully contributed to the design of short AMPs with significant bactericidal activity and cell selectivity.

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.

Adevonin, a novel synthetic antimicrobial peptide designed from the Adenanthera pavonina trypsin inhibitor (ApTI) sequence

The biological activities and the structural arrangement of adevonin, a novel antimicrobial peptide, were investigated. The trypsin inhibitor ApTI, isolated from Adenanthera pavonina seeds, was used as a template for screening 18-amino acid peptides with predicted antimicrobial activity. Adevonin presented antimicrobial activity and minimum inhibitory concentrations (MIC) ranging from 1.86 to 7.35 µM against both Gram-positive and - negative bacterial strains. Moreover, adevonin exerted time-kill effects within 10 min and both susceptible and drug-resistant bacterial strains were affected by the peptide. In vitro and in vivo assays showed that, at MIC concentration, adevonin did not affect human fibroblasts (MRC-5) viability or Galleria mellonella survival, respectively. Hemolytic activity was observed only at high peptide concentrations. Additionally, nucleic acid efflux assays, gentian violet uptake and time-kill kinetics indicate that the antimicrobial activity of adevonin may be mediated by bacterial membrane damage. Furthermore, molecular dynamic simulation in the presence of SDS micelles and anionic membrane bilayers showed that adevonin acquired a stable α-helix secondary structure. Further studies are encouraged to better understand the mechanism of action of adevonin, as well as to investigate the anti-infective activity of this peptide.

Evaluating the Bioactivity of a Novel Broad-Spectrum Antimicrobial Peptide Brevinin-1GHa from the Frog Skin Secretion of Hylarana guentheri and Its Analogues

Many antimicrobial peptides (AMPs) have been identified from the skin secretion of the frog Hylarana guentheri (H.guentheri), including Temporin, Brevinin-1, and Brevinin-2. In this study, an antimicrobial peptide named Brevinin-1GHa was identified for the first time by using ‘shotgun’ cloning. The primary structure was also confirmed through mass spectral analysis of the skin secretion purified by reversed-phase high-performance liquid chromatography (RP-HPLC). There was a Rana-box (CKISKKC) in the C-terminal of Brevinin-1GHa, which formed an intra-disulfide bridge. To detect the significance of Rana-box and reduce the hemolytic activity, we chemically synthesized Brevinin-1GHb (without Rana-box) and Brevinin-1GHc (Rana-box in central position). Brevinin-1GHa exhibited a strong and broad-spectrum antimicrobial activity against seven microorganisms, while Brevinin-1GHb only inhibited the growth of Staphylococcus aureus (S. aureus), which indicates Rana-box was necessary for the antimicrobial activity of Brevinin-1GHa. The results of Brevinin-1GHc suggested transferring Rana-box to the central position could reduce the hemolytic activity, but the antimicrobial activity also declined. Additionally, Brevinin-1GHa demonstrated the capability of permeating cell membrane and eliminating biofilm of S. aureus, Escherichia coli (E. coli), and Candida albicans (C. albicans). The discovery of this research may provide some novel insights into natural antimicrobial drug design.

Identification and functional analyses of novel antioxidant peptides and antimicrobial peptides from skin secretions of four East Asian frog species

In the present study, we identified 50 peptides that are classified into 21 peptide families with antioxidant and/or antimicrobial activity from Amolops daiyunensis, Pelophylax hubeiensis, Hylarana maosuoensis and Nanorana pleskei, which belong to four different genera in the Ranidae and Dicroglossidae families. These four frog species were found for the first time to express antioxidant peptides (AOPs) and antimicrobial peptides (AMPs). These peptides include seven newly discovered families daiyunin-1, daiyunin-2, daiyunin-3, maosonensis-1MS1, pleskein-1, pleskein-2, and pleskein-3. Antioxidant and antimicrobial activity assays showed that some of these peptides have good biological activities. For example, at a concentration of 50 μM, nigroain-B-MS1, and nigroain-C-MS1 both exhibited relatively strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonicacid) (ABTS) free radical scavenging ability, with eradication rates of 99.7% and 68.3% (nigroain-B-MS1), and 99.8% and 58.3% (nigroain-C-MS1), respectively. These peptides are potential candidates for the development of novel antioxidant or AMP preparations.

Identification and characterization of novel host defense peptides from the skin secretion of the fungoid frog, Hydrophylax bahuvistara (Anura: Ranidae)

Two novel peptides (brevinin1 HYba1 and brevinin1 HYba2) were identified from the skin secretion of the frog Hydrophylax bahuvistara, endemic to Western Ghats, India, and their amino acid sequences were confirmed using cDNA cloning and LC/MS/MS. Antibacterial, hemolytic, and cytotoxic activities of brevinin1 peptides and their synthetic analogs (amidated C-terminus) were investigated and compared. All the peptides except the acidic forms showed antibacterial activity against all tested Gram-positive and Gram-negative bacteria. They exhibited low hemolysis on human erythrocytes and showed potent cytotoxic activity against Hep 3B cancer cell line. Upon amidation, the peptides showed increased activity against the tested microbes without altering their hemolytic and cytotoxic properties. The study also emphasizes the need for screening endemic amphibian fauna of Western Ghats, as a potential source of host defense peptides with possible therapeutic applications in the future.

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.

Identification of multiple peptides with antioxidant and antimicrobial activities from skin and its secretions of Hylarana taipehensis, Amolops lifanensis, and Amolops granulosus

Amphibian skin and its secretions contain many kinds of peptides with different bioactivities. In this study, a large number of peptides including antioxidant and antimicrobial peptides were identified from three East Asian frog species Hylarana taipehensis, Amolops lifanensis, and Amolops granulosus. The majority of these peptides were antimicrobial peptides, while eight antioxidant peptides were identified, which included two novel peptides taipehensin-1TP1 (TLIWEFYHQILDEYNKENKG) and taipehensin-2TP1 (CLMARPNYRCKIFKQC). These antioxidant peptides exhibited the ability to scavenge ABTS and/or DPPH free radicals. Moreover, six out of eight antioxidant peptides temporin-TP1, brevinin-1TP1, brevinin-1TP2, brevinin-1TP3, brevinin-1LF1, and palustrin-2GN1 also showed antimicrobial activity.

An apolipoprotein E mimetic peptide with activities against multidrug-resistant bacteria and immunomodulatory effects

Apolipoprotein E (apoE) mimetic peptides derived from the low-density lipoprotein receptor-binding region of apoE with both activities against multidrug-resistant bacteria and immunomodulatory effects have not previously been reported. We identified an apoE mimetic peptide analogue of the receptor-binding region of apoE (abbreviated as apoE23) with the sequence of LRKLRKRLVRLASHLRKLRKRLL, which exhibited high antibacterial effects. The minimal inhibitory concentration of apoE23 against multidrug-resistant Acinetobacter baumannii was 6 µg/ml. The antimicrobial activity of apoE23 depended on its amphipathic α-helical conformation. Moreover, apoE23 downregulated the expression of tumour necrosis factor-α, interleukin-6 and interleukin-10 in lipopolysaccharide-induced THP-1 cells. ApoE23 exhibits potential in future clinical applications.

Database-Guided Discovery of Potent Peptides to Combat HIV-1 or Superbugs

Antimicrobial peptides (AMPs), small host defense proteins, are indispensable for the protection of multicellular organisms such as plants and animals from infection. The number of AMPs discovered per year increased steadily since the 1980s. Over 2,000 natural AMPs from bacteria, protozoa, fungi, plants, and animals have been registered into the antimicrobial peptide database (APD). The majority of these AMPs (>86%) possess 11–50 amino acids with a net charge from 0 to +7 and hydrophobic percentages between 31–70%. This article summarizes peptide discovery on the basis of the APD. The major methods are the linguistic model, database screening, de novo design, and template-based design. Using these methods, we identified various potent peptides against human immunodeficiency virus type 1 (HIV-1) or methicillin-resistant Staphylococcus aureus (MRSA). While the stepwise designed anti-HIV peptide is disulfide-linked and rich in arginines, the ab initio designed anti-MRSA peptide is linear and rich in leucines. Thus, there are different requirements for antiviral and antibacterial peptides, which could kill pathogens via different molecular targets. The biased amino acid composition in the database-designed peptides, or natural peptides such as θ-defensins, requires the use of the improved two-dimensional NMR method for structural determination to avoid the publication of misleading structure and dynamics. In the case of human cathelicidin LL-37, structural determination requires 3D NMR techniques. The high-quality structure of LL-37 provides a solid basis for understanding its interactions with membranes of bacteria and other pathogens. In conclusion, the APD database is a comprehensive platform for storing, classifying, searching, predicting, and designing potent peptides against pathogenic bacteria, viruses, fungi, parasites, and cancer cells.

Purification and characterization of a novel antimicrobial peptide from Brevibacillus laterosporus strain A60

A novel antimicrobial peptide, with molecular mass of 1602.0469Da, produced by Brevibacillus laterosporus strain A60 was isolated and purified from the soil of mango plants. The purification procedure consisted of ammonium sulfate precipitation, cation exchange chromatography on an HiTrap SP HP column, thin layer chromatography and High Performance Liquid Chromatography (HPLC) on C18 reversed-phase column. After the four isolation procedures, one peptide with antimicrobial activity was obtained and named BL-A60. The determination of the complete amino acid sequences of this peptide showed that it contains eleven amino acid residues, L-Y-K-L-V-K-V-V-L-N-M, and a choline connected to the N-terminal and a tenuazonic acid modified of the C-terminal. This peptide shows relatively low identification to other antimicrobial peptides from bacteria. Purified BL-A60 showed high pH and thermal stability and a strong inhibition of different stages of the life cycle of Phytophthora capsici, including mycelial growth, sporangia formation and cystospore germination, with EC(50) values of 7.89, 0.60 and 21.96 μg ml(-1), respectively.

Enhanced antibacterial activity of amino acids-functionalized multi walled carbon nanotubes by a simple method

Multi-walled carbon nanotubes (MWCNTs) were first functionalized by arginine and lysine under microwave radiation. Surface functionalization was confirmed by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM). After the MWCNTs were functionalized by arginine and lysine, the antibacterial activity of all treated samples was increased significantly against all bacteria that were tested. Based on the observed minimum inhibitory concentration and radial diffusion assay, the sequence of antibacterial activity was MWCNTs-arginine>MWCNTs-lysine>pristine MWCNTs. The functionalized MWCNTs were especially effective against gram-negative bacteria (e.g., Escherichia coli and Salmonella typhimurium). Interestingly, the MWCNT samples were effective against the resistant strain Staphylococcos aureus. The enhanced antibacterial activity was attributed to electrostatic adsorption of bacteria membrane due to positive charges of the functional groups on MWCNTs surface. Since MWCNTs have lower cytotoxicity than single-walled carbon nanotubes, their functionalization with cationic amino acids could be a beneficial approach in the disinfection industry.

Molecular cloning of novel antimicrobial peptide genes from the skin of the Chinese brown frog, Rana chensinensis

One species of the Chinese brown frog, Rana chensinensis, is widely distributed in north-central China. In this study, a cDNA library was constructed to clone the antimicrobial peptides' genes from the skin of R. chensinensis. Twenty-three prepropeptide cDNA sequences encoding twelve novel mature antimicrobial peptides were isolated and characterized. Six peptides belonged to three known families previously identified from other Ranid frogs: temporin (4 peptides), brevinin-2 (1 peptide), and palustrin-2 (1 peptide). The other six peptides showed little similarity to known antimicrobial peptides. According to the amino acid sequences, with or without α-helix structure, and either hydrophilic or hydrophobic, these were organized into four new families: chensinin-1 (3 peptides), chensinin-2 (1 peptide), chensinin-3 (1 peptide), and chensinin-4 (1 peptide). Five peptides from different families were chemically synthesized, and their antimicrobial, cytolytic, and hemolytic activities were evaluated. Of these, brevinin-2CE showed strongest antimicrobial activities against both the Gram-positive and Gram-negative bacteria with a slight hemolysis. Temporin-1CEe and palustrin-2CE also displayed a slight hemolysis, but they had different activities to prokaryotic cells. Temporin-1CEe showed higher antimicrobial activity against Gram-positive bacteria than Gram-negative bacteria, whereas it was contrary to palustrin-2CE. Chensinin-1 CEb and chensinin-3CE only had moderate antimicrobial activity against microorganisms. In addition, the brevinin-2 peptides from different brown frogs were analyzed to reveal the taxonomy and phylogenetic relationships of R. chensinensis.

A biochemical characterization of the major peptides from the Venom of the giant Neotropical hunting ant Dinoponera australis

Venom from the "false tocandira"Dinoponera australis, a giant Neotropical hunting ant, paralyzes small invertebrate prey and induces a myriad of systemic effects in large vertebrates. HPLC/DAD/MS analyses revealed that the venom has over 75 unique proteinaceous components with a large diversity of properties ranging in size, hydrophobicity, and overall abundance. The six most abundant peptides, demonstrative of this diversity and hereafter referred to as Dinoponeratoxins, were de novo sequenced by exact mass precursor ion selection and Edman degradation. The smallest peptide characterized, Da-1039, is hydrophilic and has similarities to vasoactive peptides like kinin and bombesin. The two largest and most abundant peptides, Da-3105 and Da-3177, have a 92.9% identity in a 28 residue overlap and share approximately 50 of their sequence with ponericin G2 (an antimicrobial from another ponerine ant Pachycondyla goeldii). One peptide, Da-1585, is a hydrophilic cleavage product of an amphipathic peptide, Da-2501. The most hydrophobic peptide, Da-1837, is amidated (a PTM observed in one half of the major peptides) and shares homology with poneratoxin, a sodium channel modifier found in the bullet ant Paraponera clavata. This study is the first examination of potential pharmacophores from venom of the genus Dinoponera (Order: Hymenoptera).