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

Abstract

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

LyeTxI-b, a Synthetic Peptide Derived From Lycosa erythrognatha Spider Venom, Shows Potent Antibiotic Activity in Vitro and in Vivo

“…Upon addition of TFE, the peptide adopts a helical conformation, as noticed by the appearance of two minima near 208 and 222 nm and a maximum near 192 nm ( Figure 2A ), which show relatively small intensities up to 20% of TFE, however, significant increases are observed in solutions containing 30–50% of TFE, which present very similar spectral profiles. This is a very common feature of linear cationic AMPs peptides, which show no conformational preferences in aqueous environments, whereas well-defined conformations are observed in the presence of organic co-solvents or other membrane mimetic environments ( Gusmao et al, 2017 ). Interestingly the spectrum obtained for the peptide in the presence of 60% of TFE is consistent with even higher helical contents.…”

“…The peptide concentration, as determined from the tryptophan molar absorptivity ( e = 5,550 M -1 cm -1 at 280 nm), was at 36.5 nmol.L -1 in all CD studies. The POPC:POPG (3:1) phospholipid vesicles were prepared as described elsewhere ( Gusmao et al, 2017 ).…”

Conformational Changes of Anoplin, W-MreB1–9, and (KFF)3K Peptides near the Membranes

“…First, we determined to what extent the peptides affect membrane disruption by monitoring the release of calcein from large unilamellar vesicles (LUVs) ( Figure 1 ). Monitoring the change of calcein fluorescence exerted by membrane-active peptides is a well-documented technique [ 31 , 40 , 41 , 42 , 43 ]. Second, we examined the antibacterial activities of the peptides by determining their minimum inhibitory concentrations (MIC) on two E. coli strains: K12 [ 44 ]—the wild type laboratory strain and BL21(DE3)—a strain deficient in the outer-membrane protease OmpT [ 39 ].…”

Antimicrobial alumina nanobiostructures of disulfide- and triazole-linked peptides: Synthesis, characterization, membrane interactions and biological activity

“…CD spectroscopy indicated that the peptides and triazole-peptides adopt random coil conformations in aqueous environments, whereas membrane-active helical arrangements are observed in the presence of phospholipid vesicles. This is a quite common feature of linear antimicrobial peptides, which present well-defined structural arrangements after membrane binding [43]. Interestingly, the nanoparticle-bound species adopt β-sheet conformations in aqueous buffer.…”