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Research article - Vol. 23, 2017 |
Ocellatin peptides from the skin secretion of the South American frog Leptodactylus labyrinthicus (Leptodactylidae): characterization, antimicrobial activities and membrane interactions
1 Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
2 Instituto de Engenharia, Ciência e Tecnologia, Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), Janaúba, MG, Brazil.
3 Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
4 Departamento de Odontologia Restauradora, Faculdade de Odontologia, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
5 Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
6 Departamento de Química, Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), Diamantina, MG, Brazil.
ABSTRACT
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.
Key words: Leptodactylus labyrinthicus; Ocellatins; Antimicrobial peptides; Peptide membrane interactions.
Funding
KAGG, MEC, PVMR, DPV and MEL acknowledge grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). DMS and VMS acknowledge grants from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). We thank CNPq, Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), Rede Mineira de Química (RQ-MG), Instituto Nacional de Ciência e Tecnologia em Toxinas (INCTOX) and PRPq-UFMG for financial support. This work was also supported by the Edital Toxinologia CAPES no. 063/2010, Process no. 230.38.006280/2011-07, AUXPE Toxinologia 1810/2011.
Received: September 21, 2016.
Revised: January 6, 2017.
Accepted: January 19, 2017.
Correspondence: jmr@ufmg.br