Ocellatin-1

Ocellatin AMPs (antimicrobial peptides) are considered to be promising alternative therapeutics to conventional antibiotics. Three-dimensional (3D) structures of ocellatin-F1 with 25 residues have been reported to be potent in terms of bacterial membrane permeability. To investigate the influence of similar ocellatin peptides with 25 residues pertaining to antimicrobial effect, ocellatin-1, K1 and S1 peptides were modelled with ocellatin-F1 as template. Comparative analyses between these peptides were carried out, using computational approaches. From the results of in silico toxicity profile, all peptides were found to be non-toxic with no haemolytic activity. Further sequence analysis, net charge, hydrophobicity and hydrophobic moment revealed the membrane permeable efficacy of ocellatin-1 peptide. Besides, the investigation of peptide electronic structures through density functional theory and quantum chemical (HOMO and LUMO) calculations predicted ocellatin-1 to be a suitable peptide, which can be used as a scaffold for therapeutics. Furthermore, the determination of structural contours such as RMSD, RMSF and Rg through trajectory analysis revealed that ocellatin-1 exhibited strong structural stability. In addition, the trajectory analysis of elements of secondary structure illustrated the alpha helical conformations to be retained in all peptides, except ocellatin-1. On the aforementioned grounds, ocellatin-1 was found to possess the important role of peptide penetration of the bacterial membrane. This study becomes significant, since it is the first time where the structural importance of ocellatin peptides were explored in detail and the therapeutic potential of ocellatin-1 as a peptide-based antimicrobial drug have been theoretically revealed.

The emergence, in recent years, of microbial resistance to commonly used antibiotics has aroused a search for new naturally occurring bactericidal and fungicidal agents that may have clinical utility. In the present study, three new antimicrobial peptides were purified from the electrical-stimulated skin secretion of the South American frog Leptodactylus ocellatus by reversed-phase chromatographic procedures. Ocellatin 1 (1GVVDILKGAGKDLLAHLVGKISEKV25-CONH2), ocellatin 2 (1GVLDIFKDAAKQILAHAAEKQI25-CONH2) and ocellatin 3 (1GVLDILKNAAKNILAHAAEQI21-CONH2) are structurally related peptides. These peptides present hemolytic activity against human erythrocytes and are also active against Escherichia coli. Ocellatins exhibit significant sequence similarity to other amphibian antimicrobial peptides, mainly to brevinin 2ED from Rana esculenta.

It is proposed that the current nomenclature by which individual antimicrobial peptides from the skins of frogs belonging to the genus Leptodactylus are named from the species of frog from which they were isolated should be replaced by one that emphasizes the fact that these peptides are evolutionarily related. As the ocellatins from Leptodactylus ocellatus were the first such peptides to be characterized, it is suggested that all orthologous peptides should be described as "ocellatins". Consistent with accepted terminology for other families of antimicrobial peptides, the upper case initial letter of the species is used to indicate their origin and isoforms are designated by numbers. When two species begin with the same initial letter, a second distinguishing letter shall be employed. Thus, the terms ocellatin-1, -2, -3, and -4 are retained for the parent peptides. Fallaxin is replaced by ocellatin-F1, pentadactylin by ocellatin-P1, laticeptin by ocellatin-L1, syphaxin by ocellatin-S1, and the paralogs from L. validus are termed ocellatin-V1, -V2, and -V3.