Influence of N-terminus modifications on the biological activity, membrane interaction, and secondary structure of the antimicrobial peptide hylin-a1

Recently the peptide Hy-a1 (IFGAILPLALGALKNLIK), with antimicrobial activity, was isolated from the skin secretion of the frog Hypsiboas albopunctatus. The aim of the present work was to evaluate four analogues with introduction of acetyl group, Asp or Lys at the N-terminus of antimicrobial peptide Hy-al to supply information about the relationship of structure-biological activity. The antimicrobial activities were assayed by measuring growth inhibition of four species of bacteria and four species of fungus. The hemolytic activity was also tested. The peptide containing Trp instead of Leu in position 6 (for fluorescence studies) presented MIC values comparable to wild type sequence: 32 μmol L(-1) , 32 μmol L(-1) , 8 μmol L(-1) , and 2 μmol L(-1) for E. coli, P. aeruginosa, S. aureus, and B. subtilis, respectively. Two peptides with this modification and containing one acetyl group or Asp residue at the N-terminal region showed activities only against Gram-positive bacteria. Different results were observed when the residue added was Lys. In this case, the activity against the microorganisms was sustained or increased. Conformational properties were investigated by CD techniques in water, TFE, and in zwitterionic micelles (LPC). The CD experiments demonstrated that, in water, the peptides had a random structure, but in TFE and LPC solutions they acquired an ordered structure, composed mainly by α-helix. However, these data have no relationship with activity against Gram-positive bacteria. These results showed that the N-terminal region of the peptide Hy-a1 has key roles in its antibacterial action toward different types of bacteria.