Comparative In-Vitro Functional Analysis of Synthetic Defensins and Their Corresponding Peptide Variants Against HIV-1NL4.3, E. coli, S. aureus and P. aeruginosa

Defensins found in mammals belong to mainly two subfamilies α- and β-defensins. Mammalian defensins are small molecules (18–45 residues) that are cysteine, arginine rich compounds. Antimicrobial activities of these peptides were shown against a wide variety of microbes including bacteria, fungi, viruses and protozoan parasites. To investigate the structure and activity relationship, amino acid substitutions that alter charge were introduced into synthetic defensin peptides by adding 2–2 Arg (RR) and Asp (DD) at both the terminal and tested their effects on HIV-1, E. coli, S. aureus, and P. aeruginosa. In the present study, we have chemically synthesized native defensin peptides and their variants with Arg (RR) and Asp (DD) amino acid residues at N- and C-termini. Later, we assayed their anti-HIV, anti-microbial activities, stability, cytotoxicity and hemolytic properties. We reported that anti-HIV and antimicrobial activities of native defensins is increased significantly by adding Arg (RR) residues at both the termini while the substitution of Arg (RR) with Asp (DD), eliminate anti-HIV and antimicrobial activity against all bacterial species tested. While other physical features i.e. stability, cell toxicity and hemolytic property were not affected by any of the changes in the sequence. The results suggest that the terminal residues in defensins are crucial functional elements that determine their microbicidal potency. The enhanced microbicidal activity observed for defensin peptides with Arg (RR) residues could be due to optimization of amphiphilicity of the structure, which could facilitate specific interactions with the microbial membranes.