Novel tryptophyllin peptides from Physalaemus centralis inhibit oxidative stress-induced endothelial dysfunction in rat aorta preparation

Amphibian skin is a rich source of molecules with biotechnological potential, including the tryptophyllin family of peptides. Here, we report the identification and characterization of two tryptophyllin peptides, FPPEWISR and FPWLLS-NH2, from the skin of the Central Dwarf Frog, Physalaemus centralis. These peptides were identified through cDNA cloning and sequence comparison. FPWLLS-NH2 shares its primary structure with a previously identified peptide from the skin of Pelophylax perezi, named PpT-2. Another peptide, FPPEWISR, is novel and was named PcT-1. After solid-phase peptide synthesis, both peptides exhibited significant antioxidant activity, with PcT-1 and PpT-2 demonstrating ABTS radical scavenging capacities of 0.305 and 0.269 mg Trolox equivalents/mg peptide, respectively, and ORAC values of 0.319 and 0.248 mg Trolox equivalents/mg peptide. Additionally, PcT-1 and PpT-2 inhibited AAPH-induced hemolysis in human red blood cells, achieving a protection level comparable to Trolox at 0.2 mg/mL. In rat aorta preparations, both peptides partially restored acetylcholine-induced vasorelaxation following pyrogallol-induced oxidative stress, with a greater protective effect of PpT-2. Hemolytic activity assay indicated no cytotoxicity in human red blood cells, and tests on Galleria mellonella larvae confirmed their low toxicity in vivo. These findings highlight the biotechnological potential of PcT-1 and PpT-2 as antioxidant agents, paving the way for new therapeutic applications in combating oxidative stress-related diseases.

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.

An unusual kynurenine-containing opioid tetrapeptide from the skin gland secretion of the Australian red tree frog Litoria rubella. Sequence determination by electrospray mass spectrometry

The Kyn-containing peptide FP-Kyn-L(NH(2)) is an unusual minor component of the skin peptide profile of the Australian red tree frog Litoria rubella collected from an area within a 20 kilometre radius of Alice Springs in central Australia. The structure was determined by electrospray mass spectrometry and synthesis. The major component of the skin secretion is the analogous tryptophyllin peptide FPWL(NH(2)). Both peptides show opioid activity at 10(-7) M, and are likely to act via the μ opioid receptor.

Novel natural peptides from Hyla arborea schelkownikowi skin secretion

Hyla arborea schelkownikowi is one of the leaf frog species inhabiting the southern territories of Russia and the former USSR. This frog species is a member of the Hylidae Rafinesque, 1815 batrachians family. The present study deals with the previously uninvestigated peptidome of the Hyla arborea schelkownikowi skin secretion. Nano-electrospray ionization Fourier transform mass spectrometry (nanoESI-FTMS) of the skin secretion, in the intact form and after acetylation, was selected as the general method of analysis. Electron-capture dissociation (ECD) and collision-induced dissociation (CID) fragmentation were both employed, while de novo sequencing was performed by manual interpretation of the MS data. The suppression of the cyclization of b-ions in the mass spectrometer by the acetylation reaction proved to be very efficient for the de novo sequencing of short peptides. Ten skin peptides were found and all of them, except for bradykinin, had not previously been reported. Six of the peptides belong to the tryptophyllins and related peptides, while three peptides are similar to the aureins.

N-terminal tagging strategy for de novo sequencing of short peptides by ESI-MS/MS and MALDI-MS/MS

The major portion of skin secretory peptidome of the European Tree frog Hyla arborea consists of short peptides from tryptophyllin family. It is known that b-ions of these peptides undergo head-to-tail cyclization, forming a ring that can open, resulting in several linear forms. As a result, the spectrum contains multiple ion series, thus complicating de novo sequencing. This was observed in the Q-TOF spectrum of one of the tryptophyllins isolated from Hyla arborea; the sequence FLPFFP-NH(2) was established by Edman degradation and counter-synthesis. Though no rearrangements were observed in FTICR-MS and MALDI-TOF/TOF spectra, both of them were not suitable for mass-spectrometry sequencing due to the low sequence coverage. To obtain full amino acid sequence by mass spectrometry, three chemical modifications to N-terminal amino moiety were applied. They include acetylation and sulfobenzoylation of N-amino group and its transformation to 2,4,6-trimethylpyridinium by interaction with 2,4,6-trimethylpyrillium tetrafluoroborate. All three reagents block scrambling and provide spectra better than the intact peptide. Unfortunately, all of them also readily react with lysine side chain. Hence, all investigated procedures can be used to improve sequencing of short peptides, while acetylation is the recommended one. It shows excellent results, and it is plain and simple to perform. This is the procedure of choice for MS-sequencing of short peptides by manual or automatic algorithms.

PdT-2: a novel myotropic type-2 tryptophyllin from the skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor

Amphibian skin secretions represent a unique resource for the discovery of new bioactive peptides. Here we report the isolation, structural and functional characterization of a novel heptapeptide amide, DMSPPWHamide, from the defensive skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor. This peptide is of unique primary structure and has been classified as a member of the rather heterogenous tryptophyllin-2 (T-2) family of amphibian skin peptides and named P. dacnicolor Tryptophyllin-2 (PdT-2) in accordance. PdT-2 is the first Type 2-tryptophyllin to possess discrete bioactivity. Both natural and synthetic replicates of the peptide were found to contract the smooth muscle of rat urinary bladder, the latter displaying an EC50 of 4 nM.

Skin peptides from anurans of the Litoria rubella Group: sequence determination using electrospray mass spectrometry. Opioid activity of two major peptides

Many species of frogs of the genus Litoria secrete bioactive peptides from their skin glands. These peptides are normally host-defence compounds and may have one, or more of the following activities; smooth muscle contraction, analgesic, antimicrobial, antiviral, lymphocyte proliferator (immunomodulator) and neuronal nitric oxide synthase (nNOS) inactivation. Two frog species of the Litoria rubella Group that have been studied before, namely, Litoria electrica and Litoria rubella, are different from other species of the genus Litoria in that they produce small peptides that show neither membrane, lymphocyte nor nNOS activity. In this study we have used electrospray mass spectrometry together with Edman sequencing to identify eight skin peptides of the third member of this Group, Litoria dentata: surprisingly, none of these peptides show activity in our biological screening program. However, two major peptides (FPWL-NH(2) and FPWP-NH(2)) from L. electrica and L. rubella are opioids at the micromolar concentration.

Amphibian skin secretomics: application of parallel quadrupole time-of-flight mass spectrometry and peptide precursor cDNA cloning to rapidly characterize the skin secretory peptidome of Phyllomedusa hypochondrialis azurea: discovery of a novel peptide family, the hyposins

This study reports the variety of peptides present in the skin secretory peptidome of Phyllomedusa hypochondrialis azurea. Peptide structures, along with post-translational modifications, were elucidated by QTOF MS/MS analysis, cDNA sequencing, or a combination of both. Twenty-two peptides, including 19 novel structures, were identified from six different structural classes, including tryptophyllins, dermorphins, and a novel group of peptides termed hyposins. The study demonstrates the power of this combined approach to mine the rich peptidome compliment of the amphibian defensive skin secretome.

Host-defence peptide profiles of the skin secretions of interspecific hybrid tree frogs and their parents, female Litoria splendida and male Litoria caerulea

Five healthy adult female first-generation hybrid tree frogs were produced by interspecific breeding of closely related tree frogs Litoria splendida and L. caerulea in a cage containing large numbers of males and females of both species. Phylogenetic analysis of mitochondrial DNA sequences established the female parent to be L. splendida. The peptide profile of the hybrid frogs included the neuropeptide caerulein, four antibiotics of the caerin 1 family and several neuronal nitric oxide synthase inhibitors of the caerin 1 and 2 classes of peptides. The skin secretions of the hybrids contained some peptides common to only one parent, some produced by both parental species, and four peptides expressed by the hybrids but not the parental species.

Bradykinin-related peptides and tryptophyllins in the skin secretions of the most primitive extant frog, Ascaphus truei

The tailed frog Ascaphus truei occupies a unique position in phylogeny as the most primitive extant anuran and is regarded as the sister taxon to the clade of all other living frogs. A previous study led to the isolation of eight antimicrobial peptides, termed ascaphins, from norepinephrine-stimulated skin secretions. Peptidomic analysis (HPLC separation followed by MALDI mass spectrometry and Edman degradation) of these secretions has led to the identification and structural characterization of 13 additional peptides present in relatively high concentration. In addition to bradykinin (BK; RPPGFSPFR), a C-terminally extended bradykinin (peptide RD-11; RPPGFSPFRVD), a bradykinin-like peptide (peptide AR-10; APVPGLSPFR), and a C-terminally extended form of this peptide (peptide AV-12; APVPGLSPFRVV) were obtained in pure form. These peptides produced concentration-dependent relaxation of precontracted mouse tracheal rings with a rank order of potency of BK>RD-11>AR-10>AV-12 but only RD-11 caused the same maximal relaxation as bradykinin. Four small peptides were also isolated from the skin secretions that contain the Pro-Trp motif that is a characteristic of the tryptophyllin family of peptides previously identified in skins of frogs of the family Hylidae. The data show that the synthesis of dermal peptides that may play a role in defense against predators arose early in the evolution of anurans.

Host-defence peptides of Australian anurans: structure, mechanism of action and evolutionary significance

Host-defence peptides secreted from the skin glands of Australian frogs and toads, are, with a few notable exceptions, different from those produced by anurans elsewhere. This review summarizes the current knowledge of the following classes of peptide isolated and characterized from Australian anurans: neuropeptides (including smooth muscle active peptides, and peptides that inhibit the production of nitric oxide from neuronal nitric oxide synthase), antimicrobial and anticancer active peptides, antifungal peptides and antimalarial peptides. Other topics covered include sex pheromones of anurans, and the application of peptide profiling to (i). recognize particular populations of anurans of the same species and to differentiate between species, and (ii). investigate evolutionary aspects of peptide formation.

Amphibian peptides that inhibit neuronal nitric oxide synthase. Isolation of lesuerin from the skin secretion of the Australian Stony Creek frog Litoria lesueuri

Two neuropeptides have been isolated and identified from the secretions of the skin glands of the Stony Creek Frog Litoria lesueuri. The first of these, the known neuropeptide caerulein 1.1, is a common constituent of anuran skin secretions, and has the sequence pEQY(SO3)TGWMDF-NH2. This neuropeptide is smooth muscle active, an analgaesic more potent than morphine and is also thought to be a hormone. The second neuropeptide, a new peptide, has been named lesueurin and has the primary structure GLLDILKKVGKVA-NH2. Lesueurin shows no significant antibiotic or anticancer activity, but inhibits the formation of the ubiquitous chemical messenger nitric oxide from neuronal nitric oxide synthase (nNOS) at IC(50) (16.2 microm), and is the first amphibian peptide reported to show inhibition of nNOS. As a consequence of this activity, we have tested other peptides previously isolated from Australian amphibians for nNOS inhibition. There are three groups of peptides that inhibit nNOS (IC(50) at microm concentrations): these are (a) the citropin/aurein type peptides (of which lesueurin is a member), e.g. citropin 1.1 (GLFDVIKKVASVIGGL-NH(2)) (8.2 microm); (b) the frenatin type peptides, e.g. frenatin 3 (GLMSVLGHAVGNVLG GLFKPK-OH) (6.8 microm); and (c) the caerin 1 peptides, e.g. caerin 1.8 (GLFGVLGSIAKHLLPHVVPVIAEKL-NH(2)) (1.7 microm). From Lineweaver-Burk plots, the mechanism of inhibition is revealed as noncompetitive with respect to the nNOS substrate arginine. When the nNOS inhibition tests with the three peptides outlined above were carried out in the presence of increasing concentrations of Ca(2+) calmodulin, the inhibition dropped by approximately 50% in each case. In addition, these peptides also inhibit the activity of calcineurin, another enzyme that requires the presence of the regulatory protein Ca(2+) calmodulin. It is proposed that the amphibian peptides inhibit nNOS by interacting with Ca(2+)calmodulin, and as a consequence, blocks the attachment of this protein to the calmodulin domain of nNOS.