Structural
changes on the buforin II increased its activity by the substitution of only a single amino acid residue [35]. The halocidin suchlike were designed and one of them, di-K19Hc emerged as the most promising candidate for the development of a new antibiotic against antibiotic-resistant bacteria, presenting both antifungal and antibacterial properties [33] and [35]. Finally structural and functional relation was evaluated by in silico theoretical analyses. In spite of all peptides showing helical structure and also hydrophobic ratio values of spectra of 20–80%, minor differences between them were evaluated here. Firstly, similar values of hydrophobic ratio and peptides studied here were observed in Antimicrobial Database (APD) for antibacterial, antifungal, antiviral and anticancer peptides [46]. The P1 peptide presented α-helix conformation with the cationic residues of lysine organized in line that favors a Cell Cycle inhibitor membrane-peptide interaction, despite a surprising absence of antibacterial activity. These data clearly show that the antibacterial activity could be related with other factors in addition to the presence of hydrophobic and cationic residues in the surface. Otherwise, P1 showed a remarkable activity toward pathogenic yeasts ( Table 2). These data could be
explained by the hydrophobic residues that are also exposed on the structure surface such as Phe1, Leu2, Leu14, Val6, and Leu18, which could interact to membrane ( Fig. 4). In Table 2 the P1 peptide demonstrates a Boman index value of −0.88 kcal mol−1, which is INCB024360 similar to aurein 2.5, an antifungal peptide from Litoria aurea and Litoria raniformis (−0.89 kcal mol−1), which shows antifungal activity toward Candida
tropicalis, Candida kefyr, Candida krusei, Candida parapsilosis and Candida glabata [49]. This peptide clearly shows the residues Leu2, Phe3, Iso5, Val6, Val9, Val10, Phe13 and Leu16 in the structural surface, showing clear homology with P1 peptide surface. Moreover, others aureins isoforms also presented similar Boman-Index with values ranging from −1.06 to 0.12 kcal mol−1, reinforcing that structures that yield similar Niclosamide Boman index values could present antifungal activity as observed for P1 peptide [38]. The P2 peptide presented a predominant α-helix conformation with cationic residues of arginine (positions 10, 13 and 16), histidine (position 12) and lysine (positions 1 and 17) exposed on the surface in the C-terminal region (Fig. 4). On the other hand, the Pro7 break the helix formation causing a turn at C-termini region. In opposite side hydrophilic residues some hydrophobic residues are also exposed on surface such as Leu4, Phe6, Val8, Val11, and Leu15. Another interesting issue consists in the homology (88%) of P2 with histone H2A.1 chain C of yeast nucleosome core structure [45]. The antimicrobial properties of histones have long been recognized despite their low activity [24].