Host-defence peptides from the glandular secretions of amphibians: structure and activity

Skin secretions of Leptodactylidae (Anura) and their potential applications

The skin of anuran species is a protective barrier against predators and pathogens, showing also chemical defense by substances that represent a potential source for bioactive substances. This review describes the current chemical and biological knowledge from the skin secretions of Leptodactylidae species, one of the most diverse neotropical frog families. These skin secretions reveal a variety of substances such as amines (12), neuropeptides (16), and antimicrobial peptides (72). The amines include histamine and its methylated derivatives, tryptamine derivatives and quaternary amines. The peptides of Leptodactylidae species show molecular weight up to 3364 Da and ocellatins are the most reported. The peptides exhibit commonly glycine (G) or glycine-valine (GV) as C-terminal amino acids, and the most common N-terminal amino acids are glutamic acid (E), lysine (K), and valine (V). The substances from Leptodactylidae species have been evaluated against pathogenic microorganisms, particularly Escherichia coli and Staphylococcus aureus, and the most active peptides showed MIC of 1-15 µM. Furthermore, some compounds showed also pharmacological properties such as immunomodulation, treatment of degenerative diseases, anticancer, and antioxidant. Currently, only 9% of the species in this family have been properly studied, highlighting a large number of unstudied species such as an entire subfamily (Paratelmatobiinae). The ecological context, functions, and evolution of peptides and amines in this family are poorly understood and represent a large field for further exploration.

Tandem Mass Spectrometry de novo Sequencing of the Skin Defense Peptides of the Central Slovenian Agile Frog Rana dalmatina

Peptides released on frogs' skin in a stress situation represent their only weapon against micro-organisms and predators. Every species and even population of frog possesses its own peptidome being appropriate for their habitat. Skin peptides are considered potential pharmaceuticals, while the whole peptidome may be treated as a taxonomic characteristic of each particular population. Continuing the studies on frog peptides, here we report the peptidome composition of the Central Slovenian agile frog Rana dalmatina population. The detection and top-down de novo sequencing of the corresponding peptides was conducted exclusively by tandem mass spectrometry without using any chemical derivatization procedures. Collision-induced dissociation (CID), higher energy collision-induced dissociation (HCD), electron transfer dissociation (ETD) and combined MS3 method EThcD with stepwise increase of HCD energy were used for that purpose. MS/MS revealed the whole sequence of the detected peptides including differentiation between isomeric Leu/Ile, and the sequence portion hidden in the disulfide cycle. The array of the discovered peptide families (brevinins 1 and 2, melittin-related peptides (MRPs), temporins and bradykinin-related peptides (BRPs)) is quite similar to that of R. temporaria. Since the genome of this frog remains unknown, the obtained results were compared with the recently published transcriptome of R. dalmatina.

EThcD Benefits for the Sequencing Inside Intramolecular Disulfide Cycles of Amphibian Intact Peptides

Disulfide bonds formed by a pair of cysteine residues in the peptides' backbone represent a certain problem for their sequencing by means of mass spectrometry. As a rule, in proteomics, disulfide bonds should be cleaved before the analysis followed by some sort of chemical derivatization. That step is time-consuming and may lead to losses of minor peptides of the analyzed mixtures due to incomplete reaction, adsorption on the walls of the vials, etc. Certain problems in the de novo top-down sequencing of amphibian skin peptides are caused by the C-terminal disulfide loop, called the Rana box. Its reduction with or without subsequent derivatization was considered to be an unavoidable step before mass spectrometry. In the present study, EThcD demonstrated its efficiency in sequencing intact disulfide-containing peptides without any preliminary derivatization. Applied to the secretion of three frog species, EThcD provided the full sequence inside the intramolecular disulfide cycle for all S-S-containing peptides found in the samples, with the only exception being diarginine species. Proteolytic fragments, which are shorter than the original peptides, were helpful in some cases. HCD should be mentioned as a complementary tool to the EThcD tool, being useful as a confirmation method for some sequence details.

Proteins from toad's parotoid macroglands: do they play a role in gland functioning and chemical defence?

BACKGROUND

Parotoid gland secretion of bufonid toads is a rich source of toxic molecules that are used against predators, parasites and pathogens. Bufadienolides and biogenic amines are the principal compounds responsible for toxicity of parotoid secretion. Many toxicological and pharmacological analyses of parotoid secretions have been performed, but little is known about the processes related to poison production and secretion. Therefore, our aim was to investigate protein content in parotoids of the common toad, Bufo bufo, to understand the processes that regulate synthesis and excretion of toxins as well as functioning of parotoid macroglands.

RESULTS

Applying a proteomic approach we identified 162 proteins in the extract from toad's parotoids that were classified into 11 categories of biological functions. One-third (34.6%) of the identified molecules, including acyl-CoA-binding protein, actin, catalase, calmodulin, and enolases, were involved in cell metabolism. We found many proteins related to cell division and cell cycle regulation (12.0%; e.g. histone and tubulin), cell structure maintenance (8.4%; e.g. thymosin beta-4, tubulin), intra- and extracellular transport (8.4%), cell aging and apoptosis (7.3%; e.g. catalase and pyruvate kinase) as well as immune (7.0%; e.g. interleukin-24 and UV excision repair protein) and stress (6.3%; including heat shock proteins, peroxiredoxin-6 and superoxide dismutase) response. We also identified two proteins, phosphomevalonate kinase and isopentenyl-diphosphate delta-isomerase 1, that are involved in synthesis of cholesterol which is a precursor for bufadienolides biosynthesis. STRING protein-protein interaction network predicted for identified proteins showed that most proteins are related to metabolic processes, particularly glycolysis, stress response and DNA repair and replication. The results of GO enrichment and KEGG analyses are also consistent with these findings.

CONCLUSION

This finding indicates that cholesterol may be synthesized in parotoids, and not only in the liver from which is then transferred through the bloodstream to the parotoid macroglands. Presence of proteins that regulate cell cycle, cell division, aging and apoptosis may indicate a high epithelial cell turnover in parotoids. Proteins protecting skin cells from DNA damage may help to minimize the harmful effects of UV radiation. Thus, our work extends our knowledge with new and important functions of parotoids, major glands involved in the bufonid chemical defence.

Two novel bombesin-like neuropeptides from the skin secretion of Pelophylax kl. esculentus: Ex vivo pharmacological characterization on rat smooth muscle types

Mammalian bombesin-like neuropeptides (BLPs) play an important role in regulation of physiological and pathophysiological processes. Frog skin-derived BLPs, of smaller size and diverse lengths and sequences at their N-terminus, have attracted the attention of many researchers. However, these N-terminal variants and the receptors modulating their pharmacological actions are poorly studied and less understood. In this study, two BLPs, namely, [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin and [Asn³, Lys⁶, Phe¹³]3–14-bombesin with primary structures NLGKQWATGHFM and NLGKQWAVGHFM were isolated from the skin secretion of hybrid Pelophylax kl. esculentus. Both BLPs share a similar primary structure with only a single amino acid substitution at the eighth position (threonine to valine), while they have quite different myotropic potencies with EC₅₀ values in the range of 22.64 ± 9.7 nM (N = 8) to 83.93 ± 46.9 nM (N = 8). The potency of [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin was approximately 3-fold higher than that of [Asn³, Lys⁶, Phe¹³]3–14-bombesin. Through the investigation of receptor selectivity using a canonical bombesin receptor antagonist, it was found that [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin and [Asn³, Lys⁶, Phe¹³]3–14-bombesin had an affinity to both BB1 and BB2 receptors. Their contractile functions are mainly modulated by both BB1 and BB2 receptors on rat urinary bladder and BB2 alone on rat uterus smooth muscle preparations. These data may provide new insights into the design of potent and selective ligands for bombesin receptors. Moreover, [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin and [Asn³, Lys⁶, Phe¹³]3–14-bombesin did not induce significant hemolysis and toxicity in normal human cells, suggesting that these two natural novel BLPs have great potential for development into new drug candidates.

Mass Spectrometry Differentiation between Rana arvalis Populations Based on Their Skin Peptidome Composition

Skin secretion of amphibians often represents the only weapon of these species against pathogens and predators. Peptides constitute the major portion of active molecules of that weapon and may be treated as potential pharmaceuticals for future generations. The first step of their efficient use involves establishing of their primary structure, i.e., sequencing. De novo sequencing by means of mass spectrometry was applied to Rana arvalis species, collected in the spring 2021 in Central Slovenia (vicinity of Ljubljana). HPLC-ESI-HRMS/MS with Orbitrap instruments was used to establish the skin peptidome of these species and compare it with the earlier identified skin peptidome of the Moscow population of Rana arvalis. Application of CID, HCD, ETD, and EThcD enabled detecting and sequencing 18 peptides; five of them were novel and may be treated as possible biomarkers of the Ljubljana population of Rana arvalis. Interestingly, representatives of two peptide families (temporins and brevinins 2) were not found in the Moscow population. MS³ modes, first of all EThcD, demonstrated their great potential in the de novo sequencing, including extraction of the sequence information from the intact peptides with disulfide cycle (rana box) in their structure and differentiation of isomeric Leu/Ile residues. Thus, all six isomeric residues were reliably distinguished in the novel melittin-related peptide AK-23-1. In addition, another post-translational modification dealing with carbonylation of the N-terminal Gly of novel temporin AVa was established using the MS³ mode. The obtained results demonstrate the efficiency of the use of MS³ tools in proteomics/peptidomics.

Molecular basis of a bacterial-amphibian symbiosis revealed by comparative genomics, modeling, and functional testing

The molecular bases for the symbiosis of the amphibian skin microbiome with its host are poorly understood. Here, we used the odor-producer Pseudomonas sp. MPFS and the treefrog Boana prasina as a model to explore bacterial genome determinants and the resulting mechanisms facilitating symbiosis. Pseudomonas sp. MPFS and its closest relatives, within a new clade of the P. fluoresens Group, have large genomes and were isolated from fishes and plants, suggesting environmental plasticity. We annotated 16 biosynthetic gene clusters from the complete genome sequence of this strain, including those encoding the synthesis of compounds with known antifungal activity and of odorous methoxypyrazines that likely mediate sexual interactions in Boana prasina. Comparative genomics of Pseudomonas also revealed that Pseudomonas sp. MPFS and its closest relatives have acquired specific resistance mechanisms against host antimicrobial peptides (AMPs), specifically two extra copies of a multidrug efflux pump and the same two-component regulatory systems known to trigger adaptive resistance to AMPs in P. aeruginosa. Subsequent molecular modeling indicated that these regulatory systems interact with an AMP identified in Boana prasina through the highly acidic surfaces of the proteins comprising their sensory domains. In agreement with a symbiotic relationship and a highly selective antibacterial function, this AMP did not inhibit the growth of Pseudomonas sp. MPFS but inhibited the growth of another Pseudomonas species and Escherichia coli in laboratory tests. This study provides deeper insights into the molecular interaction of the bacteria-amphibian symbiosis and highlights the role of specific adaptive resistance toward AMPs of the hosts.

FT-MS in the de novo top-down sequencing of natural nontryptic peptides

The present review covers available results on the application of FT-MS for the de novo sequencing of natural peptides of various animals: cones, bees, snakes, amphibians, scorpions, and so forth. As these peptides are usually bioactive, the animals efficiently use them as a weapon against microorganisms or higher animals including predators. These peptides represent definite interest as drugs of future generations since the mechanism of their activity is completely different in comparison with that of the modern antibiotics. Utilization of those peptides as antibiotics can eliminate the problem of the bacterial resistance development. Sequence elucidation of these bioactive peptides becomes even more challenging when the species genome is not available and little is known about the protein origin and other properties of those peptides in the study. De novo sequencing may be the only option to obtain sequence information. The benefits of FT-MS for the top-down peptide sequencing, the general approaches of the de novxxo sequencing, the difficult cases involving sequence coverage, isobaric and isomeric amino acids, cyclization of short peptides, the presence of posttranslational modifications will be discussed in the review.

The Arsenal of Bioactive Molecules in the Skin Secretion of Urodele Amphibians

Urodele amphibians (∼768 spp.), salamanders and newts, are a rich source of molecules with bioactive properties, especially those isolated from their skin secretions. These include pharmacological attributes, such as antimicrobial, antioxidant, vasoactive, immune system modulation, and dermal wound healing activities. Considering the high demand for new compounds to guide the discovery of new drugs to treat conventional and novel diseases, this review summarizes the characteristics of molecules identified in the skin of urodele amphibians. We describe urodele-derived peptides and alkaloids, with emphasis on their biological activities, which can be considered new scaffolds for the pharmaceutical industry. Although much more attention has been given to anurans, bioactive molecules produced by urodeles have the potential to be used for biotechnological purposes and stand as viable alternatives for the development of therapeutic agents.

Caerin 1.1 and 1.9 Peptides from Australian Tree Frog Inhibit Antibiotic-Resistant Bacteria Growth in a Murine Skin Infection Model

The host defense peptide caerin 1.9 was originally isolated from skin secretions of an Australian tree frog and inhibits the growth of a wide range of bacteria in vitro. In this study, we demonstrated that caerin 1.9 shows high bioactivity against several bacteria strains, such as Staphylococcus aureus, Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus haemolyticus in vitro. Importantly, unlike the antibiotic Tazocin, caerin 1.9 does not induce bacterial resistance after 30 rounds of in vitro culture. Moreover, caerin 1.1, another peptide of the caerin family, has an additive antibacterial effect when used together with caerin 1.9. Furthermore, caerin 1.1 and 1.9 prepared in the form of a temperature-sensitive gel inhibit MRSA growth in a skin bacterial infection model of two murine strains. These results indicate that caerin 1.1 and 1.9 peptides could be considered an alternative for conventional antibiotics. IMPORTANCE Antibiotic-resistant bacteria cause severe problems in the clinic. We show in our paper that two short peptides isolated from an Australian frog and prepared in the form of a gel are able to inhibit the growth of antibiotic-resistant bacteria in mice, and, unlike antibiotics, these peptides do not lead to the development of peptide-resistant bacteria strains.

Manual mass spectrometry de novo sequencing of the anionic host defense peptides of the Cuban Treefrog Osteopilus septentrionalis

RATIONALE

Host defense peptides accumulated in the skin glands of the animals constitute the basis of the adaptive and immune system of amphibians. The peptidome of the Cuban frog Osteopilus septentrionalis was established using tandem mass spectrometry as the best analytical tool to elucidate the sequence of these peptides.

METHODS

Manual interpretation of complementary collision-induced dissociation (CID), higher energy collision-induced dissociation (HCD), and electron transfer dissociation (ETD) tandem mass spectra recorded with an Orbitrap Elite mass spectrometer in liquid chromatography/mass spectrometry (LC/MS) mode was used to sequence the peptide components of the frog skin secretion, obtained by mild electrostimulation.

RESULTS

Although the vast majority of amphibian peptides discovered so far are cationic, surprisingly only anionic peptides were identified in the skin secretion of the Cuban frog Osteopilus septentrionalis. Mass spectrometry allowed the sequences to be established of 16 representatives of new peptide families: septenins 1 and septenins 2. The highest sequence coverage when dealing with these anionic peptides was obtained with CID normalized collision energy 35 and HCD normalized collision energy 28.

CONCLUSIONS

Mirror-symmetrical peptides are sequenced using N-terminal acetylation. Acetylated Ser is reliably distinguished from isomeric Glu by the loss of ketene from b-ions containing the corresponding residue. Calculations of the physicochemical and structural properties of the discovered anionic septenins 1 and 2 allowed the mechanism of their interaction with microbe cells to be postulated.

Total synthesis and in vivo evaluation of 8-deoxypumiliotoxin 193H

The total synthesis of both the double bond isomers of indolizine alkaloid 8-deoxypumiliotoxin 193H has been accomplished. Both the double bond isomers Z-4 and E-4 induced convulsions and inhibited neuro-muscular activity at a dose of 25 mg/kg after intraperitoneal injection in mice. The lethal dose of Z-4 and E-4 was 100 mg/kg, indicating that 8-deoxypumiliotoxin 193H is 10-times less toxic than the known pumiliotoxin (+)-251 D.

Antioxidant activities of major tryptophyllin L peptides: A joint investigation of Gaussian-based 3D-QSAR and radical scavenging experiments

The red tree frog Litoria rubella from Australia has been studied for several decades showing that their dorsal skin glands secrete a number of small peptides containing a Pro-Trp sequence, known as tryptophyllin L peptides. Although peptides from many genera of Australian frogs have been reported to possess a variety of biological activities, the bioactivities of this peptide family have remained to be discovered. In this study, we investigated the antioxidant potency of a number of tryptophyllin L peptides for the first time using a joint statistical and experimental approach in which predictions based on Gaussian three-dimensional quantitative structure-activity relationship (3D-QSAR) models were employed to guide an in vitro experimental investigation. Two tryptophyllin tripeptides P-W-L (OH) and P-W-L (NH₂ ) were predicted to have the Trolox equivalent antioxidant capacity (TEAC) values of 0.80 and 0.87 μM Trolox/μM peptide, respectively. With those promising results, antioxidant capabilities of five tryptophyllin L peptides with the common core Pro-Trp-Leu were synthesized and subjected to 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing ability of plasma (FRAP) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS˙⁺ ) radical scavenging assays. The tests indicated that all the tested tryptophyllin L peptides, noticeably S-P-W-L (OH) and F-P-W-L (NH₂ ), are strong ABTS˙⁺ radical scavengers and moderate scavengers in the other two assays. The results, thus, suggested that the tryptophyllin L peptides are likely to be a part of the skin antioxidant system helping the frog to cope with drastic change in oxygen exposure and humidity, as they inhabit over a large area of Australia with a wide climate variation.

Identification of New Ocellatin Antimicrobial Peptides by cDNA Precursor Cloning in the Frame of This Family of Intriguing Peptides

Ocellatins are a family of antimicrobial peptides found exclusively in the Leptodactylus genus. To date, 10 species have been studied and more than 23 peptides described. Here we report the sequences of five new peptides from the skin of the frog Leptodactylus latrans (Anura: Leptodactylidae) determined by cDNA cloning of the complete prepro-peptide structures. The mature peptides were characterized with in silico tools and compared with those previously described. With 21 amino acid residues, this new set of peptides not previously described in the Leptodactylus genus share between 100 and 76.2% similarity to ocellatin antimicrobial peptides. These novel peptides are cationic and their three-dimensional (3D) structure holds the highly conserved residues G¹, D⁴, K⁷, and K¹¹ and a high theoretical amphipathic α-helix content. Furthermore, in silico analyses of these new peptides predicted antimicrobial activity. This study is framed in the context of previous work published about ocellatins, and therefore, provides a review of this intriguing family of peptides.

Design, Engineering and Discovery of Novel α-Helical and β-Boomerang Antimicrobial Peptides against Drug Resistant Bacteria

In an era where the pipeline of new antibiotic development is drying up, the continuous rise of multi-drug resistant (MDR) and extensively drug resistant (XDR) bacteria are genuine threats to human health. Although antimicrobial peptides (AMPs) may serve as promising leads against drug resistant bacteria, only a few AMPs are in advanced clinical trials. The limitations of AMPs, namely their low in vivo activity, toxicity, and poor bioavailability, need to be addressed. Here, we review engineering of frog derived short α-helical AMPs (aurein, temporins) and lipopolysaccharide (LPS) binding designed β-boomerang AMPs for further development. The discovery of novel cell selective AMPs from the human proprotein convertase furin is also discussed.

Diversity of Antimicrobial Peptides in Three Partially Sympatric Frog Species in Northeast Asia and Implications for Evolution

Antimicrobial peptides (AMPs) are evolutionarily ancient molecules that play an essential role in innate immunity across taxa from invertebrates to vertebrates. The evolution system of AMP system has not been well explained in the literature. In this study, we cloned and sequenced AMP transcriptomes of three frog species, namely Rana dybowskii, Rana amurensis, and Pelophylax nigromaculatus, which are partially sympatric in northeast Asia, but show different habitat preferences. We found that each species contained 7 to 14 families of AMPs and the diversity was higher in species with a large geographic range and greater habitat variation. All AMPs are phylogenetically related but not associated with the speciation process. Most AMP genes were under negative selection. We propose that the diversification and addition of novel functions and improvement of antimicrobial efficiency are facilitated by the expansion of family members and numbers. We also documented significant negative correlation of net charges and numbers of amino acid residues between the propiece and mature peptide segments. This supports the Net Charge Balance Hypothesis. We propose the Cut Point Sliding Hypothesis as a novel diversification mechanism to explain the correlation in lengths of the two segments.

Adsorption of Amyloidogenic Peptides to Functionalized Surfaces Is Biased by Charge and Hydrophilicity

Surfaces are abundant in living systems, such as in the form of cellular membranes, and govern many biological processes. In this study, the adsorption of the amyloidogenic model peptides GNNQQNY, NNFGAIL, and VQIVYK as well as the amyloid-forming antimicrobial peptide uperin 3.5 (U3.5) were studied at low concentrations (100 μM) to different surfaces. The technique of a quartz crystal microbalance with dissipation monitoring (QCM-D) was applied as it enables the monitoring of mass binding to sensors at nanogram sensitivity. Gold-coated quartz sensors were used as unmodified gold surfaces or functionalized with self-assembled monolayers (SAMs) of alkanethiols (terminated as methyl, amino, carboxyl, and hydroxyl) resulting in different adsorption affinities of the peptides. Our objective was to evaluate the underlying role of the nature and feature of interfaces in biological systems which could concentrate peptides and impact or trigger peptide aggregation processes. In overall, the largely hydrophobic peptides adsorbed with preference to hydrophobic or countercharged surfaces. Further, the glycoprotein lubricin (LUB) was tested as an antiadhesive coating. Despite its hydrophilicity, the adsorption of peptides to LUB coated sensors was similar to the adsorption to unmodified gold surfaces, which indicates that some peptides diffused through the LUB layer to reach the underlying gold sensor surface. The LUB protein-antiadhesive is thus more effective as a biomaterial coating against larger biomolecules than small peptides under the conditions used here. This study provides directions toward a better understanding of amyloid peptide adsorption to biologically relevant interfaces, such as cellular membranes.

A Hylarana latouchii Skin Secretion-Derived Novel Bombesin-Related Pentadecapeptide (Ranatensin-HLa) Evoke Myotropic Effects on the in vitro Rat Smooth Muscles

Amphibians have developed successful defensive strategies for combating predators and invasive microorganisms encountered in their broad range of environments, which involve secretion of complex cocktails of noxious, toxic and diverse bioactive molecules from the skins. In recent years, amphibian skin secretions have been considered as an extraordinary warehouse for the discovery of therapeutic medicines. In this study, through bioactivity screening of the Hylarana latouchii skin secretion-derived fractions, a novel peptide belonging to ranatensin subfamily (ranatensin-HLa) was discovered, and structurally and pharmacologically-characterised. It consists of 15 amino acid residues, pGlu-NGDRAPQWAVGHFM-NH₂, and its synthetic replicate was found to exhibit pharmacological activities on increasing the contraction of the in vitro rat bladder and uterus smooth muscles. Corresponding characteristic sigmoidal dose-response curves with EC₅₀ values of 7.1 nM and 5.5 nM were produced, respectively, in bladder and uterus. Moreover, the precursor of ranatensin-HLa showed a high degree of similarity to those of bombesin-like peptides from Odorrana grahami and Odorrana schmackeri. Hylarana latouchii skin continues to serve as a storehouse with diverse lead compounds for the development of therapeutically effective medicines.

Could Cardiolipin Protect Membranes against the Action of Certain Antimicrobial Peptides? Aurein 1.2, a Case Study

The activity of a host of antimicrobial peptides has been examined against a range of lipid bilayers mimicking bacterial and eukaryotic membranes. Despite this, the molecular mechanisms and the nature of the physicochemical properties underlying the peptide-lipid interactions that lead to membrane disruption are yet to be fully elucidated. In this study, the interaction of the short antimicrobial peptide aurein 1.2 was examined in the presence of an anionic cardiolipin-containing lipid bilayer using molecular dynamics simulations. Aurein 1.2 is known to interact strongly with anionic lipid membranes. In the simulations, the binding of aurein 1.2 was associated with buckling of the lipid bilayer, the degree of which varied with the peptide concentration. The simulations suggest that the intrinsic properties of cardiolipin, especially the fact that it promotes negative membrane curvature, may help protect membranes against the action of peptides such as aurein 1.2 by counteracting the tendency of the peptide to induce positive curvature in target membranes.

Identification of novel antimicrobial peptide from Asian sea bass (Lates calcarifer) by in silico and activity characterization

Background

The global crisis of antibiotic resistance increases the demand for the new promising alternative drugs such as antimicrobial peptides (AMPs). Accordingly, we have described a new, previously unrecognized effective AMP, named dicentracin-like, from Asian sea bass and characterized its antimicrobial activity by comparison with moronecidin.

Methodology/ Results

Gene expression analysis demonstrated the expression of dicentracin-like peptide in tissues of the immune system such as the skin and the head kidney, which is an important endocrine and lymphoid organ. Moronecidin and dicentracin-like exhibited a higher antibacterial activity against gram-positive bacteria relative to gram-negative ones, while both peptides showed a greater binding ability to gram-negative bacteria compared to gram-positive ones. This contradiction between antibacterial activity and binding affinity may be related to the outer membrane from gram-negative bacteria. Compared with moronecidin, dicentracin-like peptide showed more potent binding ability to all gram-positive and gram-negative bacteria. In addition, dicentracin-like peptide exhibited a high antibacterial activity against the investigated microorganisms, except against Staphylococcus aureus. A direct relationship was found between the binding affinity/cationicity and the antibiofilm activity of the peptides wherein, an elevation in pH corresponded to a decrease in their antibiofilm property. Time-kill kinetics analysis against clinical Acinetobacter baumannii isolate indicated that bactericidal effect of dicentracin-like and moronecidin at inhibitory concentration (1XMIC) was observed after 4 and 6 hours, respectively, while bactericidal effect of both AMPs at concentration of 2XMIC was observed after 2 hours. Dicentracin-like peptide showed higher inhibitory activity at subinhibitory concentration (1/2XMIC), relative to moronecidin. Compared with moronecidin, dicentracin-like peptide possessed greater binding affinity to bacteria at high salt concentration, as well as at alkaline pH; In addition, dicentracin-like exhibited a higher antibiofilm activity in comparison to moronecidin even at alkaline pH. Hemolytic analysis against human RBC revealed that hemolytic activity of moronecidin was more potent than that of dicentracin-like, which is consistent with its greater non-polar face hydrophobicity.

Conclusions

In the present study, In Silico comparative sequence analysis and antimicrobial characterization led to identify a new, previously unrecognized antimicrobial function for named dicentracin-like peptide by comparison with moronecidin, representing a possible template for designing new effective AMPs and improving known ones.

Identification and bioactivity analysis of a newly identified defensin from the oyster Magallana gigas

The relatively conserved sequences of signal peptides and proregions that antimicrobial peptides (AMPs) contain have been successfully used to search for and identify novel AMPs from databases within the same lineages of fish and amphibians and across different animal classes. If such an approach is applicable to invertebrate species such as oyster has not yet been tested so far. In this study, we found a cDNA from the digestive gland of the oyster Magallana gigas, designated Mgdefdg, which contains two exons interspaced by one intron. Mgdefdg coded for a protein with features characteristic of defensins. The mature peptide had the cysteine-stabilized α-helix/β-sheet motif (CSαβ) and the consensus pattern C-X_5-6-C-X₃-C-X_4-6-C-X_3-4-C-X_7-8-C-X-C-X₂-C forming potential disulfide linkages C1-C5, C2-C6, C3-C7 and C4-C8 in the predicted tertiary structure. Functional assays revealed that recombinant mature MgDefdg (rmMgDefdg) was able to kill the Gram-negative bacterium Aeromonas hydrophila and the Gram-positive bacterium Staphylococcus aureus, and to induce bacterial membrane/cytoplasmic damage. ELISA showed that rmMgDefdg had high affinity to both A. hydrophila and S. aureus as well as the microbe-associated molecular pattern molecules LPS and LTA. Moreover, rmMgDefdg was capable of causing bacterial membrane permeabilization and depolarization, and intracellular ROS increase. Additionally, rmMgDefdg was not cytotoxic to human red blood cells and murine RAW264.7 cells. Taken together, our results indicate that MgDefdg is a previously uncharacterized defensin with membrane selectivity towards bacterial cells. It also shows that the use of conserved sequences of signal peptides of defensins can be an effective tool to identify potential defensins across different animal genera in invertebrates.

Skin glands of an aquatic salamander vary in size and distribution and release antimicrobial secretions effective against chytrid fungal pathogens

Amphibian skin is unique among vertebrate classes, containing a large number of multicellular exocrine glands that vary among species and have diverse functions. The secretions of skin glands contain a rich array of bioactive compounds including antimicrobial peptides (AMPs). Such compounds are important for amphibian innate immune responses and may protect some species from chytridiomycosis, a lethal skin disease caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). While the bioactivity of skin secretions against Bd has been assessed for many amphibian taxa, similar studies are lacking for Bsal, a chytrid fungus that is especially pathogenic for salamanders. We studied the skin glands and their potential functions in an aquatic salamander, the three-toed amphiuma (Amphiuma tridactylum). Skin secretions of captive adult salamanders were analyzed by RP-HPLC and tested against the growth of Bd and Bsal using in vitro assays. We found that compounds within collected skin secretions were similar between male and female salamanders and inhibited the growth of Bd and Bsal. Thus, skin secretions that protect against Bd may also provide protection against Bsal. Histological examination of the skin glands of preserved salamanders revealed the presence of enlarged granular glands concentrated within caudal body regions. A site of potential gland specialization was identified at the tail base and may indicate specialized granular glands related to courtship and communication.

Cleavage of Peptides from Amphibian Skin Revealed by Combining Analysis of Gland Secretion and in Situ MALDI Imaging Mass Spectrometry

Peptides from skin secretions of amphibians are considered important components of their immune system and also play a relevant role in their defense mechanism against predators. Herein, by using mass spectrometry (MS), we characterize the sequence of 13 peptides from the gland secretion of the hylid tree frog, Boana punctata. Using in situ matrix-assisted laser desorption ionization imaging MS of a transverse section of the skin tissue, we show that some peptides are stored as longer molecules that are cleaved after being secreted, whereas others do not undergo any modification. Sequence comparison with peptides from other Boana species and analysis of the three-dimensional theoretical structure indicate that this cleavage depends on both the presence of a specific sequence motif and the secondary structure. The fact that peptides undergo a rapid cleavage upon secretion suggests that stored and secreted peptides may have distinct roles for anuran survival, including defense against pathogens and predators.

Comparative Proteomic Study of the Antiproliferative Activity of Frog Host-Defence Peptide Caerin 1.9 and Its Additive Effect with Caerin 1.1 on TC-1 Cells Transformed with HPV16 E6 and E7

Caerin is a family of peptides isolated from the glandular secretion of Australian tree frogs, the genus Litoria, and has been previously shown to have anticancer activity against several cancer cells. In this work, we used two host-defence peptides, caerin 1.1 and caerin 1.9, to investigate their ability to inhibit a murine derived TC-1 cell transformed with human papillomavirus 16 E6 and E7 growth in vitro. Caerin 1.9 inhibits TC-1 cell proliferation, although inhibition is more pronounced when applied in conjunction with caerin 1.1. To gain further insights into the antiproliferative mechanisms of caerin 1.9 and its additive effect with caerin 1.1, we used a proteomics strategy to quantitatively examine (i) the changes in the protein profiles of TC-1 cells and (ii) the excretory-secretory products of TC-1 cells following caerin peptides treatment. Caerin 1.9 treatment significantly altered the abundance of several immune-related proteins and related pathways, such as the Tec kinase and ILK signalling pathways, as well as the levels of proinflammatory cytokines and chemokines. In conclusion, caerin peptides inhibit TC-1 cell proliferation, associated with modification in signalling pathways that would change the tumour microenvironment which is normally immune suppressive.

EThcD Discrimination of Isomeric Leucine/Isoleucine Residues in Sequencing of the Intact Skin Frog Peptides with Intramolecular Disulfide Bond

Our scientific interests involve de novo sequencing of non-tryptic natural amphibian skin peptides including those with intramolecular S-S bond by means of exclusively mass spectrometry. Reliable discrimination of the isomeric leucine/isoleucine residues during peptide sequencing by means of mass spectrometry represents a bottleneck in the workflow for complete automation of the primary structure elucidation of these compounds. MS³ is capable of solving the problem. Earlier we demonstrated the advanced efficiency of ETD-HCD method to discriminate Leu/Ile in individual peptides by consecutive application of ETD to the polyprotonated peptides followed by HCD applied to the manually selected primary z-ions with the targeted isomeric residues at their N-termini and registration of the characteristic w-ions. Later this approach was extended to deal with several (4-7) broad band mass ranges, without special isolation of the primary z-ions. The present paper demonstrates an advanced version of this method when EThcD is applied in the whole mass range to a complex mixture of natural non-tryptic peptides without their separation and intermediate isolation of the targeted z-ions. The proposed EThcD method showed over 81% efficiency for the large natural peptides with intact disulfide ring, while the interfering process of radical site migration is suppressed. Due to higher speed and sensitivity, the proposed EThcD approach facilitates the analytical procedure and allows for the automation of the entire experiment and data processing. Moreover, in some cases it gives a chance to establish the nature of the residues in the intact intramolecular disulfide loops. Graphical Abstract ᅟ.

Genital warts treatment: Beyond imiquimod

Genital warts are one of the most common sexually transmitted diseases worldwide. The disease is a result of infection with low-risk types of human papillomaviruses, mostly type 6 and 11. Current therapies for genital warts are mainly ablative, or alternatively topical application of imiquimod cream and sinecatechin (polyphenon E) ointment to the warts. However, low patient compliance and high recurrence rate are significant problems for the treatment of genital warts by imiquimod and ablative therapies. We summarise recent literature in this area and propose combining imiquimod with other therapies to increase the efficacy of imiquimod.

Negative ion cleavages of (M-H)- anions of peptides. Part 3. Post-translational modifications

It is now 25 years since we commenced the study of the negative-ion fragmentations of peptides and we have recently concluded this research with investigations of the negative-ion chemistry of most post-translational functional groups. Our first negative-ion peptide review (Bowie, Brinkworth, & Dua, 2002) dealt with the characteristic backbone fragmentations and side-chain cleavages from (M-H)^- ions of underivatized peptides, while the second (Bilusich & Bowie, 2009) included negative-ion backbone cleavages for Ser and Cys and some initial data on some post-translational groups including disulfides. This third and final review provides a brief summary of the major backbone and side chain cleavages outlined before (Bowie, Brinkworth, & Dua, 2002) and describes the quantum mechanical hydrogen tunneling associated with some proton transfers in enolate anion/enolate systems. The review then describes, in more depth, the negative-ion cleavages of the post-translational groups Kyn, isoAsp, pyroglu, disulfides, phosphates, and sulfates. Particular emphasis is devoted to disulfides (both intra- and intermolecular) and phosphates because of the extensive and spectacular anion chemistry shown by these groups. © 2016 Wiley Periodicals, Inc. Mass Spec Rev.

High-Throughput Identification of Antimicrobial Peptides from Amphibious Mudskippers

Widespread existence of antimicrobial peptides (AMPs) has been reported in various animals with comprehensive biological activities, which is consistent with the important roles of AMPs as the first line of host defense system. However, no big-data-based analysis on AMPs from any fish species is available. In this study, we identified 507 AMP transcripts on the basis of our previously reported genomes and transcriptomes of two representative amphibious mudskippers, Boleophthalmus pectinirostris (BP) and Periophthalmus magnuspinnatus (PM). The former is predominantly aquatic with less time out of water, while the latter is primarily terrestrial with extended periods of time on land. Within these identified AMPs, 449 sequences are novel; 15 were reported in BP previously; 48 are identically overlapped between BP and PM; 94 were validated by mass spectrometry. Moreover, most AMPs presented differential tissue transcription patterns in the two mudskippers. Interestingly, we discovered two AMPs, hemoglobin β1 and amylin, with high inhibitions on Micrococcus luteus. In conclusion, our high-throughput screening strategy based on genomic and transcriptomic data opens an efficient pathway to discover new antimicrobial peptides for ongoing development of marine drugs.

Discovery of Phylloseptins that Defense against Gram-Positive Bacteria and Inhibit the Proliferation of the Non-Small Cell Lung Cancer Cell Line, from the Skin Secretions of Phyllomedusa Frogs

The growing occurrence of bacterial resistance to conventional antibiotics has called for the development of new classes of antimicrobial agents. Antimicrobial peptides (AMPs) with broad antimicrobial spectrum derived from frog skin secretions have been demonstrated to be promising candidates for new antibiotic development. A proven rich source of these compounds are the skin secretions of the frogs in the Phyllomedusa genus. In this study, two novel phylloseptin peptides—phylloseptin-PTa and phylloseptin-PHa—were isolated from the skin secretions of the South American frogs, Phyllomedusa tarsius (P. tarsius) and Phyllomedusa hypochondrialis (P. hypochondrialis) through parallel transcriptomic and peptidomic studies. Replicates obtained by chemical synthesis were structurally analysed and shown to adopt an α-helix configuration in an amphiphilic environment. Both peptides demonstrated antimicrobial activities against planktonic Gram-positive bacteria strains, including Staphylococcus aureus, Enterococcus faecalis and methicillin-resistant Staphylococcus aureus , biofilms, as well as cytostatic effects on the non-small cell lung cancer cell line, NCI-H157, with relatively low haemolysis on horse erythrocytes and low cytotoxicity on the human microvascular endothelial cell line, HMEC-1. The discovery of phylloseptin peptides may further inspire the development of new types of antibiotics.

Peptides, Peptidomimetics, and Polypeptides from Marine Sources: A Wealth of Natural Sources for Pharmaceutical Applications

Nature provides a variety of peptides that are expressed in most living species. Evolutionary pressure and natural selection have created and optimized these peptides to bind to receptors with high affinity. Hence, natural resources provide an abundant chemical space to be explored in peptide-based drug discovery. Marine peptides can be extracted by simple solvent extraction techniques. The advancement of analytical techniques has made it possible to obtain pure peptides from natural resources. Extracted peptides have been evaluated as possible therapeutic agents for a wide range of diseases, including antibacterial, antifungal, antidiabetic and anticancer activity as well as cardiovascular and neurotoxin activity. Although marine resources provide thousands of possible peptides, only a few peptides derived from marine sources have reached the pharmaceutical market. This review focuses on some of the peptides derived from marine sources in the past ten years and gives a brief review of those that are currently in clinical trials or on the market.

Identification of Miscellaneous Peptides from the Skin Secretion of the European Edible Frog, Pelophylax kl. Esculentus

The chemical compounds synthesised and secreted from the dermal glands of amphibian have diverse bioactivities that play key roles in the hosts' innate immune system and in causing diverse pharmacological effects in predators that may ingest the defensive skin secretions. As new biotechnological methods have developed, increasing numbers of novel peptides with novel activities have been discovered from this source of natural compounds. In this study, a number of defensive skin secretion peptide sequences were obtained from the European edible frog, P. kl. esculentus, using a 'shotgun' cloning technique developed previously within our laboratory. Some of these sequences have been previously reported but had either obtained from other species or were isolated using different methods. Two new skin peptides are described here for the first time. Esculentin-2c and Brevinin-2Tbe belong to the Esculentin-2 and Brevinin-2 families, respectively, and both are very similar to their respective analogues but with a few amino acid differences. Further, [Asn-3, Lys-6, Phe-13] 3-14-bombesin isolated previously from the skin of the marsh frog, Rana ridibunda, was identified here in the skin of P. kl. esculentus. Studies such as this can provide a rapid elucidation of peptide and corresponding DNA sequences from unstudied species of frogs and can rapidly provide a basis for related scientific studies such as those involved in systematic or the evolution of a large diverse gene family and usage by biomedical researchers as a source of potential novel drug leads or pharmacological agents.

Structure and membrane interactions of the homodimeric antibiotic peptide homotarsinin

Antimicrobial peptides (AMPs) from amphibian skin are valuable template structures to find new treatments against bacterial infections. This work describes for the first time the structure and membrane interactions of a homodimeric AMP. Homotarsinin, which was found in Phyllomedusa tarsius anurans, consists of two identical cystine-linked polypeptide chains each of 24 amino acid residues. The high-resolution structures of the monomeric and dimeric peptides were determined in aqueous buffers. The dimer exhibits a tightly packed coiled coil three-dimensional structure, keeping the hydrophobic residues screened from the aqueous environment. An overall cationic surface of the dimer assures enhanced interactions with negatively charged membranes. An extensive set of biophysical data allowed us to establish structure-function correlations with antimicrobial assays against Gram-positive and Gram-negative bacteria. Although both peptides present considerable antimicrobial activity, the dimer is significantly more effective in both antibacterial and membrane biophysical assays.

Evidences for the action mechanism of angiotensin II and its analogs on Plasmodium sporozoite membranes

Malaria is an infectious disease responsible for approximately one million deaths annually. Oligopeptides such as angiotensin II (AII) and its analogs are known to have antimalarial effects against Plasmodium gallinaceum and Plasmodium falciparum. However, their mechanism of action is still not fully understood at the molecular level. In the work reported here, we investigated this issue by comparing the antimalarial activity of AII with that of (i) its diastereomer formed by only d-amino acids; (ii) its isomer with reversed sequence; and (iii) its analogs restricted by lactam bridges, the so-called VC5 peptides. Data from fluorescence spectroscopy indicated that the antiplasmodial activities of both all-D-AII and all-D-VC5 were as high as those of the related peptides AII and VC5, respectively. In contrast, retro-AII had no significant effect against P. gallinaceum. Conformational analysis by circular dichroism suggested that AII and its active analogs usually adopted a β-turn conformation in different solutions. In the presence of membrane-mimetic micelles, AII had also a β-turn conformation, while retro-AII was random. Molecular dynamics simulations demonstrated that the AII chains were slightly more bent than retro-AII at the surface of a model membrane. At the hydrophobic membrane interior, however, the retro-AII chain was severely coiled and rigid. AII was much more flexible and able to experience both straight and coiled conformations. We took it as an indication of the stronger ability of AII to interact with membrane headgroups and promote pore formation.

Molecular mechanisms mediating the beneficial metabolic effects of [Arg4]tigerinin-1R in mice with diet-induced obesity and insulin resistance

The frog skin host-defense peptide tigerinin-1R stimulates insulin release in vitro and improves glucose tolerance and insulin sensitivity in animal models of type 2 diabetes. This study extends these observations by investigating the molecular mechanisms of action underlying the beneficial metabolic effects of the analogue [Arg4]tigerinin-1R in mice with diet-induced obesity, glucose intolerance and insulin resistance. The study also investigates the electrophysiological effects of the peptide on KATP and L-type Ca2+ channels in BRIN-BD11 clonal β cells. Non-fasting plasma glucose and glucagon concentrations were significantly (p<0.05) decreased and plasma insulin increased by twice daily treatment with [Arg4]tigerinin-1R (75 nmol/kg body weight) for 28 days. Oral and intraperitoneal glucose tolerance were significantly (p<0.05) improved accompanied by enhanced secretion and action of insulin. The peptide blocked KATP channels and, consistent with this, improved beta cell responses of isolated islets to a range of secretagogues. Peptide administration resulted in up-regulation of key functional genes in islets involved insulin secretion (Abcc8, Kcnj11, Cacna1c and Slc2a2) and in skeletal muscle involved with insulin action (Insr, Irs1, Pdk1, Pik3ca, and Slc2a4). These observations encourage further development of tigerinin-1R analogues for the treatment of patients with type 2 diabetes.

Baltikinin: A New Myotropic Tryptophyllin-3 Peptide Isolated from the Skin Secretion of the Purple-Sided Leaf Frog, Phyllomedusa baltea

Here we report the identification of a novel tryptophyllin-3 peptide with arterial smooth muscle relaxation activity from the skin secretion of the purple-sided leaf frog, Phyllomedusa baltea. This new peptide was named baltikinin and had the following primary structure, pGluDKPFGPPPIYPV, as determined by tandem mass spectrometry (MS/MS) fragmentation sequencing and from cloned skin precursor-encoding cDNA. A synthetic replicate of baltikinin was found to have a similar potency to bradykinin in relaxing arterial smooth muscle (half maximal effective concentration (EC₅₀) is 7.2 nM). These data illustrate how amphibian skin secretions can continue to provide novel potent peptides that act through functional targets in mammalian tissues.

Identification and functional characterization of an uncharacterized antimicrobial peptide from a ciliate Paramecium caudatum

The global ever-growing concerns about multi-drug resistant (MDR) microbes leads to urgent demands for exploration of new antibiotics including antimicrobial peptides (AMPs). Here we demonstrated that a cDNA from Ciliata Paramecium caudatum, designated Pcamp1, coded for a protein with features characteristic of AMPs, which is not homologous to any AMPs currently known. Both the C-terminal 91 amino acid residues of PcAMP1, cPcAMP1, expressed in Escherichia coli and the C-terminal 26 amino acid residues (predicted mature AMP), cPcAMP1/26, synthesized, underwent a coil-to-helix transition in the presence of TFE, SDS or DPC. Functional assays revealed that cPcAMP1 and cPcAMP1/26 were both able to kill Aeromonas hydrophila and Staphylococcus aureus. ELISA showed that cPcAMP1 and cPcAMP1/26 were able to bind to microbe-associated molecular pattern molecules LPS and LTA, which was further corroborated by the observations that cPcAMP1 could deposit onto the bacterial membranes. Importantly, both cPcAMP1 and cPcAMP1/26 were able to induce bacterial membrane permeabilization and depolarization, and to increase intracellular ROS levels. Additionally, cPcAMP1 and cPcAMP1/26 were not cytotoxic to mammalian cells. Taken together, our results show that PcAMP1 is a potential AMP with a membrane selectivity towards bacterial cells, which renders it a promising template for the design of novel peptide antibiotics against MDR microbes. It also shows that use of signal conserved sequence of AMPs can be an effective tool to identify potential AMPs across different animal classes.

Kunitzins: Prototypes of a new class of protease inhibitor from the skin secretions of European and Asian frogs

Amphibian skin secretions contain biologically-active compounds, such as anti-microbial peptides and trypsin inhibitors, which are used by biomedical researchers as a source of potential novel drug leads or pharmacological agents. Here, we report the application of a recently developed technique within our laboratory to "shotgun" clone the cDNAs encoding two novel but structurally-related peptides from the lyophilised skin secretions of one species of European frog, Rana esculenta and one species of Chinese frog, Odorrana schmackeri. Bioanalysis of the peptides established the structure of a 17-mer with an N-terminal Ala (A) residue and a C-terminal Cys (C) residue with a single disulphide bridge between Cys 12 and 17, which is a canonical Kunitz-type protease inhibitor motif (-CKAAFC-). Due to the presence of this structural attribute, these peptides were named kunitzin-RE (AAKIILNPKFRCKAAFC) and kunitzin-OS (AVNIPFKVHLRCKAAFC). Synthetic replicates of these two novel peptides were found to display a potent inhibitory activity against Escherichia coli but were ineffective at inhibiting the growth of Staphylococcus aureus and Candida albicans at concentrations up to 160 μM, and both showed little haemolytic activity at concentrations up to 120 μM. Subsequently, kunitzin-RE and kunitzin-OS were found to be a potent inhibitor of trypsin with a Ki of 5.56 μM and 7.56 μM that represent prototypes of a novel class of highly-attenuated amphibian skin protease inhibitor. Substitution of Lys-13, the predicted residue occupying the P1 position within the inhibitory loop, with Phe (F) resulted in decrease in trypsin inhibitor effectiveness and antimicrobial activity against Esherichia coli, but exhibits a potential inhibition activity against chymotrypsin.

Biological activities of skin and parotoid gland secretions of bufonid toads (Bufo bufo, Bufo verrucosissimus and Bufotes variabilis) from Turkey

Toad glandular secretions and skin extractions contain numerous natural agents which may provide unique resources for novel drug development. Especially the skin-parotoid gland secretions of toads from genus Bufo contain as many as 86 different types of active compounds, each with the potential of becoming a potent drug. In the present study, crude skin-parotoid gland secretions from Bufo bufo, Bufo verrucosissimus and Bufotes variabilis from Turkey were screened against various cancer cells together with normal cells using MTT assay. Furthermore, the antimicrobial properties of skin secretions were tested on selected bacterial and fungal species for assessing the possible medical applications. Antimicrobial activity of skin secretions was studied by determining minimal inhibitory concentration (MIC) in broth dilution method. Hemolytic activity of each skin-secretion was also estimated for evaluating pharmaceutical potential. Both skin-parotoid gland secretions showed high cytotoxic effect on all cancerous and non-cancerous cell lines with IC50 values varying between <0.1μg/ml and 6.02μg/ml. MIC results of antimicrobial activity tests were found to be between 3.9μg/ml and 250μg/ml. No hemolytic activities on rabbit red blood cells at concentrations between 0.5μg/ml and 50μg/ml were observed. In conclusion, skin-parotoid secretions of bufonid toads might be remarkable candidates for anti-cancer and antimicrobial agents without hemolytic activities.

LTQ Orbitrap Velos in routine de novo sequencing of non-tryptic skin peptides from the frog Rana latastei with traditional and reliable manual spectra interpretation

RATIONALE

Mass spectrometry has shown itself to be the most efficient tool for the sequencing of peptides. However, de novo sequencing of novel natural peptides is significantly more challenging in comparison with the same procedure applied for the tryptic peptides. To reach the goal in this case it is essential to select the most efficient methods of triggering fragmentation and combine all the possible complementary techniques.

METHODS

Collision-induced dissociation (CID), high-energy collision dissociation (HCD), and electron-transfer dissociation (ETD) tandem mass spectra recorded with a LTQ Orbitrap Velos instrument were used for the elucidation of the sequence of the natural non-tryptic peptides from the skin secretion of Rana latastei. Manual interpretation of the spectra was applied.

RESULTS

The combined approach using CID, HCD, and ETD tandem mass spectra of the multiprotonated peptides in various charge states, as well as of their proteolytic fragments, allowed the sequences of seven novel peptides from the skin secretion of Rana latastei to be established.

CONCLUSIONS

Manual mass spectrometry sequencing of natural non-tryptic peptides from the skin secretion of Rana latastei provided the opportunity to work successfully with these species and demonstrated once again its advantage over automatic approaches.

Identification of a novel antimicrobial peptide from amphioxus Branchiostoma japonicum by in silico and functional analyses

The emergence of multi-drug resistant (MDR) microbes leads to urgent demands for novel antibiotics exploration. We demonstrated a cDNA from amphioxus Branchiostoma japonicum, designated Bjamp1, encoded a protein with features typical of antimicrobial peptides (AMPs), which is not homologous to any AMPs currently discovered. It was found that Bjamp1 was expressed in distinct tissues, and its expression was remarkably up-regulated following challenge with LPS and LTA. Moreover, the synthesized putative mature AMP, mBjAMP1, underwent a coil-to-helix transition in the presence of TFE or SDS, agreeing well with the expectation that BjAMP1 was a potential AMP. Functional assays showed that mBjAMP1 inhibited the growth of all the bacteria tested, and induced membrane/cytoplasmic damage. ELISA indicated that mBjAMP1 was a pattern recognition molecule capable of identifying LPS and LTA. Importantly, mBjAMP1 disrupted the bacterial membranes by a membranolytic mechanism. Additionally, mBjAMP1 was non-cytotoxic to mammalian cells. Collectively, these data indicate that mBjAMP1 is a new AMP with a high bacterial membrane selectivity, rendering it a promising template for the design of novel peptide antibiotics against MDR microbes. It also shows for the first time that use of signal conserved sequence of AMPs is effective identifying potential AMPs across different animal classes.

The Amyloid Fibril-Forming Properties of the Amphibian Antimicrobial Peptide Uperin 3.5

The amphibian skin is a vast resource for bioactive peptides, which form the basis of the animals' innate immune system. Key components of the secretions of the cutaneous glands are antimicrobial peptides (AMPs), which exert their cytotoxic effects often as a result of membrane disruption. It is becoming increasingly evident that there is a link between the mechanism of action of AMPs and amyloidogenic peptides and proteins. In this work, we demonstrate that the broad-spectrum amphibian AMP uperin 3.5, which has a random-coil structure in solution but adopts an α-helical structure in membrane-like environments, forms amyloid fibrils rapidly in solution at neutral pH. These fibrils are cytotoxic to model neuronal cells in a similar fashion to those formed by the proteins implicated in neurodegenerative diseases. The addition of small quantities of 2,2,2-trifluoroethanol accelerates fibril formation by uperin 3.5, and is correlated with a structural stabilisation induced by this co-solvent. Uperin 3.5 fibril formation and the associated cellular toxicity are inhibited by the polyphenol (-)-epigallocatechin-3-gallate (EGCG). Furthermore, EGCG rapidly dissociates fully formed uperin 3.5 fibrils. Ion mobility-mass spectrometry reveals that uperin 3.5 adopts various oligomeric states in solution. Combined, these observations imply that the mechanism of membrane permeability by uperin 3.5 is related to its fibril-forming properties.