A novel heterodimeric antimicrobial peptide from the tree-frog Phyllomedusa distincta

We present here the purification and the analysis of the structural and functional properties of distinctin, a 5.4 kDa heterodimeric peptide with antimicrobial activity from the tree-frog Phyllomedusa distincta. This peptide was isolated from the crude extract of skin granular glands by different chromatographic steps. Its minimal inhibitory concentration was determined against pathogenic Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa strains. Amino acid sequencing and mass spectrometric investigations demonstrated that distinctin is constituted of two different polypeptide chains connected by an intermolecular disulphide bridge. Circular dichroism and Fourier-transformed infrared spectroscopy studies showed that this molecule adopts, in water, a structure containing a significant percentage of anti-parallel beta-sheet. A conformational variation was observed under experimental conditions mimicking a membrane-like environment. Database searches did not show sequence similarities with any known antimicrobial peptides. In the light of these results, we can consider distinctin as the first example of a new class of antimicrobial heterodimeric peptides from frog skin.

Antimicrobial peptides from the Brazilian frog Phyllomedusa distincta

Different peptides were purified by chromatographic procedures from the skin-secretory glands of the frog Phyllomedusa distincta. These are the first peptides reported from this frog species. Their primary structure was determined by a combination of automated Edman degradation and mass spectrometry. Peptide Q2 contains 25 amino acid residues, peptide Q1 and L have 28 each, peptide M contains 31, and peptide K has 33 amino acid residues. They all showed potent antimicrobial activity against Gram-negative and Gram-positive bacteria, presenting minimal inhibitory concentrations from 0.6 to 40 microM, when tested against Enterococcus faecalis, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Peptides K, L, and Q1 were chemically synthesized and shown to be active.

A tetrodotoxin-like substance found in the Brazilian frog Brachycephalus ephippium

A tetrodotoxin-like substance, denoted ephippiotoxin, was obtained from the tissue of Brachycephalus ephippium, a small pumpkin-coloured frog collected in the Atlantic Forest of the southeast region of Brazil. Ephippiotoxin is a dialyzable substance soluble in water, methanol and ethanol, but insoluble in organic solvents such as chloroform and other apolar solvents. After treatment with active charcoal (Norit-A) and purification with ion-exchange Amberlite IRC-50 resin (NH4 + form), a freeze-dried residue was obtained, with a toxicity of c. 117 micrograms/kg (mice, i.p.). Ephippiotoxin showed the same mobility as crystalline tetrodotoxin (Sankyo) when submitted to thin-layer chromatography (silica gel G) using seven different solvent systems. White mice (20 +/- 1 g) injected i.p. with either B. ephippium tissue extracts or semi-purified toxin showed partial paralysis of the hind limbs, lethargy, altered breathing rhythm and clonic convulsions. Death occurred within 1.5-30 min after injection, depending on the dose. Ephippiotoxin induced atrioventricular diastolic blockade in the toad heart. It also inhibited the response of toad striated muscle to direct and indirect electric stimulation and blocked the compound action potential of isolated frog sciatic nerve.

Indirect cardiotoxic activity of the caecilian Siphonops paulensis (Gymnophiona, Amphibia) skin secretion

The skin secretion of the caecilian S. paulensis has an indirect cardiotoxic effect. It induces a rapid blockage of electrical activity and subsequent diastolic arrest on in situ toad heart preparations. This action is not blocked by atropine and is therefore not mediated through a cholinergic mechanism. In addition, S. paulensis skin secretion is ineffective in inducing any response in isolated perfused toad heart assay, in the spontaneously beating isolated toad atria or in the electrically driven toad ventricle strip. These results, and the observation that S. paulensis skin secretion exhibits an hemolytic activity ([Schwartz, E. F., Schwartz, C. A., Sebben, A., Mendes E. G. (1997) Cardiotoxic and hemolytic activities on the caecilian Siphonops paulensis skin secretion. J. Venom. Anim. Toxins 3(1), 190]), suggest that the skin secretion cardiotoxicity could be mediated through an endogenous agent. The cardiotoxic action of S. paulensis skin secretion was investigated in isolated toad cardiac tissues in the presence of toad red blood cells (TRBC). In both atria and ventricle it evoked the same responses observed in the in situ heart. The potassium concentrations of the suspending media, as determined by atomic absorption spectroscopy were 9.5 and 11.7 times greater, respectively, in the presence of TRBC than in its absence. Given that increased levels of potassium also showed a negative inotropic effect in the isolated ventricle strip, the action of the skin secretion was attributed to the hemolytic activity, which causesan increase in K+ concentration of the medium.

Osteologia de Melanosuchus niger (Crocodylia: Alligatoridae) e a evidência evolutiva

RESUMO: O objetivo foi realizar a descrição anatômica do esqueleto de Melanosuchus niger, com o intuito de contribuir com informações evolutivas sobre a espécie. Utilizaram-se três espécimes adultos de M. niger, com comprimento médio de 2,40m, provenientes da coleção biológica do Lapas-UFU. Na cintura peitoral, a escápula é maior do que o coracóide. Já nos elementos da cintura pelvina, o púbis não participa da formação do acetábulo, o contato com o ilío, ocorre por ligamentos, e sua articulação com o ísquio, permite movimentos dorso-ventrais. Nos membros torácicos, o úmero figura como elemento do estilopódio, a ulna e rádio como elementos do zeugopódio. No carpo há o ulnar do carpo, fusão do radial+intermédio, fusão dos distais do carpo 3+4+5 e o pisiforme; possui cinco metacarpos, numerados lateromedialmente e a fórmula falângica 2:3:4:3:2. Nos membros pelvinos, o estilopódio é formado pelo fêmur e o zeugopódio pela tíbia e fíbula. No tarso há a fusão do intermédio+central, fibular do tarso, distal do tarso 3, distal do tarso 4; possui quatro metatarsos longos I, II, III e IV, sendo os metatarsos II e III maiores que os demais. O metatarso V é um osso bastante reduzido e o pé possui a fórmula falângica 2:3:4:4. No crânio, a abertura nasal é única, o palatino, vômer, pterigóide, pré-maxila e maxila formam a estrutura óssea do palato secundário; o osso parietal é o único elemento no teto craniano. No esqueleto pós- axial em pares de costelas distintas que se articulam com as vértebras cervicais, dorsais, lombares, sacrais e caudais. A gastrália é formada por sete fileiras de ossos finos localizados entre o púbis e a região caudal do esterno.

Occurrence of hemolytic activity in the skin secretion of the caecilian siphonops paulensis

The skin secretion of the caecilian Siphonops paulensis (SpSS) induces a time-and dose-dependent hemolytic response on red blood cells (RBC). When RBC from various animals species were subjected to the action of SpSS, a range of sensitivities was evident, sheep erythrocytes being the most susceptible, human, mouse and rabbit having moderate susceptibility, cow, snake and toad erythrocytes being more resistant, while S. paulensis RBC were entirely resistant. The hemolytic activity of SpSS was inhibited at temperatures higher than 60 degrees C. Both trypsin- and chymotrypsin-treated SpSS were ineffective in inducing RBC lysis. The treatment of SpSS with sheep RBC ghosts reduced its activity. There is no phospholipase activity in the SpSS.

The peptide secreted at the water to land transition in a model amphibian has antioxidant effects

In addition to the morphophysiological changes experienced by amphibians during metamorphosis, they must also deal with a different set of environmental constraints when they shift from the water to the land. We found that Pithecopus azureus secretes a single peptide ([M + H]+ = 658.38 Da) at the developmental stage that precedes the onset of terrestrial behaviour. De novo peptide and cDNA sequencing revealed that the peptide, named PaT-2, is expressed in tandem and is a member of the tryptophyllins family. In silico studies allowed us to identify the position of reactive sites and infer possible antioxidant mechanisms of the compounds. Cell-based assays confirmed the predicted antioxidant activity in mammalian microglia and neuroblast cells. The potential neuroprotective effect of PaT-2 was further corroborated in FRET-based live cell imaging assays, where the peptide prevented lipopolysaccharide-induced ROS production and glutamate release in human microglia. In summary, PaT-2 is the first peptide expressed during the ontogeny of P. azureus, right before the metamorphosing froglet leaves the aquatic environment to occupy terrestrial habitats. The antioxidant activity of PaT-2, predicted by in silico analyses and confirmed by cell-based assays, might be relevant for the protection of the skin of P. azureus adults against increased O₂ levels and UV exposure on land compared with aquatic environments.

Ontogeny of the Appendicular Skeleton in Melanosuchus niger (Crocodylia: Alligatoridae)

The objective of the present study was to analyze chondrogenesis and the ossification pattern of the limbs of Melanosuchus niger in order to contribute with possible discussions on homology and the fusion pattern of autopodial elements and phylogeny. In the Reserva Extrativista do Lago Cuniã, Rondônia, Brazil, six nests were marked and two eggs removed from each nest at 24-hour intervals until hatching. Embryos were cleared using KOH; bone tissue was stained with alizarin red S and cartilage with Alcian blue. Routine staining with HE was also performed. In the pectoral girdle, the scapula showed ossification centers before the coracoid process. In the pelvic girdle, the ilium and the ischium were condensed as a single cartilage, although ossification took place through two separate centers, forming distinct elements in the adult. The pubis developed from an independent cartilaginous center with free end, which reflects its function in breathing. In the initial stages, the stylopodium and the zeugopodium developed from the condensation of a Y-shaped cartilage in the limbs, and differentiation of the primary axis and digital arch were observed. The greatest changes were observed in the mesopodia. In their evolution, Crocodylia underwent a vast reduction in the number of autopodial elements as a consequence of fusions and ossification of some elements. This study shows that the chondrogenesis and ossification sequences are dissociated. Moreover, the differences between M. niger and other species show clear variation in the patterns for these events in Alligatoridae.

Ontogeny of the skull of the Black Caiman (Melanosuchus niger) (Crocodylia: Alligatoridae)

We describe the formation of the chondrocranium and the ossification pattern of the skull of the Black Caiman (Melanosuchus niger (Spix, 1825)). The embryos were cleared and double-stained with Alizarin Red S and Alcian Blue 8GX. Additionally, they were visualized by histological hematoxylin and eosin staining and computed tomography imaging. The chondrocranium of M. niger comprised the nasal capsule, orbitotemporal, and optic–occipital regions. Its development began at stage 9, with the chondrification of the acrochordal cartilage, trabeculae, and mandibular cartilage. The optic capsule was formed in the caudolateral portion of the chondrocranium at stage 13. The basal plate appeared at stage 14, with foramina for the hypoglossal. The chondrocranium was completely formed at stage 16. The first osteogenic events were noted at stage 13, in the bones, maxilla, jugal, postorbital, and pterygoid. The quadratojugal, prefrontal, frontal, and squamosal began their ossification at stage 14. The parietal bone began to ossify only at stage 20. The basisphenoid began at stage 15 and the parasphenoid began at stage 16. The jaw bones ossified between stages 13 and 16. The dermal elements started their ossification prior to the endochondral bones.