The crude skin secretion of the pepper frog Leptodactylus labyrinthicus is rich in metallo and serine peptidases

Cutaneous glands of the striped toad, Rhinella crucifer (Wied-Neuwied, 1821) (Amphibia: Bufonidae): Histological study and bioactivities of glandular secretions

This study investigated the morphology of Rhinella crucifer cutaneous glands, as well as the protein/peptide profiles and bioactivities of body gland secretions (BGS) and parotoid macrogland secretions (PS). The parotoid as well as dorsal and ventral skin fragments of male and female individuals were processed for histological analysis. The protein and peptide profiles of male and female gland secretions were evaluated. Male secretions were also assessed for proteolytic, trypsin inhibiting, hemagglutinating, hemolytic, antimicrobial, and anticoagulant activities. The R. crucifer skin structure presented protuberances that are clearly visible and formed by the integument, which has cutaneous glands throughout the body. An average of 438 and 333 glands were identified in males in females, respectively. No significant differences were observed in the distribution of glands across the body as well as for area and perimeter of glands. Differences were observed in protein composition between the PS and BGS from males and females, and secretions from animals collected from undisturbed and anthropogenically disturbed areas. Proteins with similarities to catalase and elongation factor 1-alpha were detected in the PS. Zymography revealed proteolytic activity in both male BGS and PS. Male BGS showed antibacterial activity against Enterococcus faecalis and Escherichia coli and anticoagulant activity, being able to prolong prothrombin time by 6.34-fold and activated partial thromboplastin time by 2.17-fold. Finally, male PS and BGS caused a maximum hemolysis degree of 1.4%. The data showed that the cutaneous secretions of R. crucifer are potentially promising for biotechnological prospecting.

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.

Mapping Salivary Proteases in Sjögren's Syndrome Patients Reveals Overexpression of Dipeptidyl Peptidase-4/CD26

Sjögren's Syndrome (SS) is an autoimmune exocrinopathy characterized by the progressive damage of salivary and lacrimal glands associated with lymphocytic infiltration. Identifying new non-invasive biomarkers for SS diagnosis remains a challenge, and alterations in saliva composition reported in patients turn this fluid into a source of potential biomarkers. Among these, proteases are promising candidates since they are involved in several key physio-pathological processes. This study evaluated differentially expressed proteases in SS individuals' saliva using synthetic fluorogenic substrates, zymography, ELISA, and proteomic approaches. Here we reported, for the first time, increased activity of the serine protease dipeptidyl peptidase-4/CD26 (DPP4/CD26) in pSS saliva, the expression level of which was corroborated by ELISA assay. Gelatin zymograms showed that metalloproteinase proteolytic band profiles differed significantly in intensity between control and SS groups. Focusing on matrix metalloproteinase-9 (MMP9) expression, an increased tendency in pSS saliva (p = 0.0527) was observed compared to the control group. Samples of control, pSS, and sSS were analyzed by mass spectrometry to reveal a general panorama of proteases in saliva. Forty-eight protein groups of proteases were identified, among which were the serine proteases cathepsin G (CTSG), neutrophil elastase (ELANE), myeloblastin (PRTN3), MMP9 and several protease inhibitors. This work paves the way for proteases to be explored in the future as biomarkers, emphasizing DPP4 by its association in several autoimmune and inflammatory diseases. Besides its proteolytic role, DPP4/CD26 acts as a cell surface receptor, signal transduction mediator, adhesion and costimulatory protein involved in T lymphocytes activation.

Biochemical characterization and cytotoxic effect of the skin secretion from the red-spotted Argentina frog Argenteohyla siemersi (Anura: Hylidae)

Background:

Argenteohyla siemersi (red-spotted Argentina frog) is a casque-headed tree frog species belonging to the Hylidae family. This species has a complex combination of anti-predator defense mechanisms that include a highly lethal skin secretion. However, biochemical composition and biological effects of this secretion have not yet been studied.

Methods:

The A. siemersi skin secretion samples were analyzed by mass spectrometry and chromatographic analysis (MALDI-TOF/MS, RP-HPLC and GC-MS). Proteins were also studied by SDS-PAGE. Among the biological activities evaluated, several enzymatic activities (hemolytic, phospholipase A₂, clotting, proteolytic and amidolytic) were assessed. Furthermore, the cytotoxic activity (cytolysis and fluorescence staining) was evaluated on myoblasts of the C2C12 cell line.

Results:

The MALDI-TOF/MS analysis identified polypeptides and proteins in the aqueous solution of A. siemersi skin secretion. SDS-PAGE revealed the presence of proteins with molecular masses from 15 to 55 kDa. Steroids, but no alkaloids or peptides (less than 5 KDa), were detected using mass spectrometry. Skin secretion revealed the presence of lipids in methanolic extract, as analyzed by CG-MS. This secretion showed hemolytic and phospholipase A₂ activities, but was devoid of amidolytic, proteolytic or clotting activities. Moreover, dose-dependent cytotoxicity in cultured C2C12 myoblasts of the skin secretion was demonstrated. Morphological analysis, quantification of lactate dehydrogenase release and fluorescence staining indicated that the cell death triggered by this secretion involved necrosis.

Conclusions:

Results presented herein evidence the biochemical composition and biological effects of A. siemersi skin secretion and contribute to the knowledge on the defense mechanisms of casque-headed frogs.

The Amphibian Diacylglycerol O-acyltransferase 2 (DGAT2): a 'paleo-protein' with Conserved Function but Unique Folding

Amphibians are, currently, considered the first vertebrates that had performed the aquatic to terrestrial transition during evolution; therefore, water balance and dehydration control were prerequisites for such environment conquering. Among anurans, Phyllomedusa is a well-studied genus, due to its peptide-rich skin secretion. Here, we have analyzed the skin secretion of Phyllomedusa distincta targeting the proteins present in the skin secretion. The major soluble protein was chromatographically isolated and utilized to immunize rabbits. Through proteomics approaches, we were able to identify such protein as being the diacylglycerol O-acyltransferase 2 (DGAT2), a crucial enzyme involved in lipid synthesis and in the skin water balance. Immunohistochemistry assays revealed the protein tissular distribution for different animal species, belonging to different branches of the phylogenetic tree. Specifically, there was positivity to the anti-DGAT2 on Amphibians' skin, and no antibody recognition on fish and mammals' skins. The DGAT2 multiple sequence alignment reveals some degree of conservation throughout the genera; however, there is a different cysteine pattern among them. Molecular modeling analyses corroborate that the different cysteine pattern leads to distinct 3D structures, explaining the different antibody recognition. Moreover, the protein phylogenetic analyses place the Xenopus DGAT2 (the available amphibian representative) next to the Coelacanthus enzyme, which have led the authors to term this a 'paleo-protein'. DGAT2 would be, therefore, an ancient protein, crucial to the terrestrial environment conquest, with a unique folding-as indicated by the molecular models and immunohistochemistry analyses-a consequence of the different cysteine pattern but with conserved biological function.

Transcriptomic and Proteomic Analyses Reveal the Diversity of Venom Components from the Vaejovid Scorpion Serradigitus gertschi

To understand the diversity of scorpion venom, RNA from venomous glands from a sawfinger scorpion, Serradigitus gertschi, of the family Vaejovidae, was extracted and used for transcriptomic analysis. A total of 84,835 transcripts were assembled after Illumina sequencing. From those, 119 transcripts were annotated and found to putatively code for peptides or proteins that share sequence similarities with the previously reported venom components of other species. In accordance with sequence similarity, the transcripts were classified as potentially coding for 37 ion channel toxins; 17 host defense peptides; 28 enzymes, including phospholipases, hyaluronidases, metalloproteases, and serine proteases; nine protease inhibitor-like peptides; 10 peptides of the cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 protein superfamily; seven La1-like peptides; and 11 sequences classified as "other venom components". A mass fingerprint performed by mass spectrometry identified 204 components with molecular masses varying from 444.26 Da to 12,432.80 Da, plus several higher molecular weight proteins whose precise masses were not determined. The LC-MS/MS analysis of a tryptic digestion of the soluble venom resulted in the de novo determination of 16,840 peptide sequences, 24 of which matched sequences predicted from the translated transcriptome. The database presented here increases our general knowledge of the biodiversity of venom components from neglected non-buthid scorpions.

Novel Kazal-type proteinase inhibitors from the skin secretion of the Splendid leaf frog, Cruziohyla calcarifer

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18 novel Kazal proteins were identified in skin secretions of Cruziohyla calcarifer.

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CCKPs share the C-X₍₇₎-C-X_(6,7)-C-X_(6,7)-Y-X₍₃₎-C-X₍₂₎-C-X_(15-21)-C pattern.

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Trypsin and chymotrypsin inhibitory activity was proposed for 5 types of CCKPs.

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CCKP-1 has trypsin inhibitory activity and molecular mass of [M+H]⁺ = 5926.43 Da.

Peptidase inhibitors have an important role controlling a variety of biological processes. Here, we employed a peptidomic approach including molecular cloning, tandem mass spectrometry and enzymatic assays to reveal 7 Kazal-type proteinase inhibitors (CCKPs) (18 variants) in the skin secretion of the unexplored frog, Cruziohyla calcarifer. All 18 proteins shared the Kazal pattern C-X₍₇₎-C-X_(6,7)-C-X_(6,7)-Y-X₍₃₎-C-X₍₂₎-C-X_(15-21)-C and 3 disulphide bridges. Based on structural comparative analysis, we deemed trypsin and chymotrypsin inhibitory activity in CCKP-1, 4 and CCKP 2, 5, 7, respectively. These peptidase inhibitors presumably play a role to control the balance between other functional peptides produced in the amphibian skin secretions.

Ocellatin peptides from the skin secretion of the South American frog Leptodactylus labyrinthicus (Leptodactylidae): characterization, antimicrobial activities and membrane interactions

Background

The availability of antimicrobial peptides from several different natural sources has opened an avenue for the discovery of new biologically active molecules. To the best of our knowledge, only two peptides isolated from the frog Leptodactylus labyrinthicus, namely pentadactylin and ocellatin-F1, have shown antimicrobial activities. Therefore, in order to explore the antimicrobial potential of this species, we have investigated the biological activities and membrane interactions of three peptides isolated from the anuran skin secretion.

Methods

Three peptide primary structures were determined by automated Edman degradation. These sequences were prepared by solid-phase synthesis and submitted to activity assays against gram-positive and gram-negative bacteria and against two fungal strains. The hemolytic properties of the peptides were also investigated in assays with rabbit blood erythrocytes. The conformational preferences of the peptides and their membrane interactions have been investigated by circular dichroism spectroscopy and liposome dye release assays.

Results

The amino acid compositions of three ocellatins were determined and the sequences exhibit 100% homology for the first 22 residues (ocellatin-LB1 sequence). Ocellatin-LB2 carries an extra Asn residue and ocellatin-F1 extra Asn-Lys-Leu residues at C-terminus. Ocellatin-F1 presents a stronger antibiotic potential and a broader spectrum of activities compared to the other peptides. The membrane interactions and pore formation capacities of the peptides correlate directly with their antimicrobial activities, i.e., ocellatin-F1 > ocellatin-LB1 > ocellatin-LB2. All peptides acquire high helical contents in membrane environments. However, ocellatin-F1 shows in average stronger helical propensities.

Conclusions

The obtained results indicate that the three extra amino acid residues at the ocellatin-F1 C-terminus play an important role in promoting stronger peptide-membrane interactions and antimicrobial properties. The extra Asn-23 residue present in ocellatin-LB2 sequence seems to decrease its antimicrobial potential and the strength of the peptide-membrane interactions.

Electronic supplementary material

The online version of this article (doi:10.1186/s40409-017-0094-y) contains supplementary material, which is available to authorized users.

Animal-microbe interactions and the evolution of nervous systems

Animals ubiquitously interact with environmental and symbiotic microbes, and the effects of these interactions on animal physiology are currently the subject of intense interest. Nevertheless, the influence of microbes on nervous system evolution has been largely ignored. We illustrate here how taking microbes into account might enrich our ideas about the evolution of nervous systems. For example, microbes are involved in animals' communicative, defensive, predatory and dispersal behaviours, and have likely influenced the evolution of chemo- and photosensory systems. In addition, we speculate that the need to regulate interactions with microbes at the epithelial surface may have contributed to the evolutionary internalization of the nervous system.