Structure-function studies of amphiphilic antibacterial peptides

Abstract

The synthesis of 11 peptides, ranging in composition from 9 to 17 amino acid residues, by solid-phase methodology was accomplished with the purpose of studying how the amphiphilic and hydrophobic character, the size of the molecule, and the charge distribution modulate the antibacterial activity. It was found that peptides composed of 16 and 17 amino acid residues, with high hydrophobic (mainly due to Trp or Phe) and hydrophilic (due to Lys) character distributed along opposite amphiphilic faces, showed considerable antibacterial activity against clinically isolated bacteria together with Gram positive and Gram negative ATCC bacterial strains. However, the hemolytic capacity of the peptides was also significant. Decreasing the hydrophobic character of the molecule by replacing Trp or Phe with Leu residues while maintaining the basic contribution of Lys drastically reduced the hemolytic activity and only slightly decreased the bioactivity. Peptides composed of 9-10 amino acid residues with high hydrophobic and basic nature possess antibacterial activity but, in general, are less active than the larger counterpart peptides. By replacing all Trp residues of a short peptide by Leu residues, the activity was considerably reduced. Circular dichroism studies and antibacterial assays showed that shorter peptides with very low helical content, and thus deprived of amphiphilic character, still have appreciable bioactivity. This observation, coupled with the fact that due to their small size they cannot span the bacterial outer lipid bilayer, may suggest different mechanisms of action for long-chain vis-a-vis short-chain peptides.

Peptoids that mimic the structure, function, and mechanism of helical antimicrobial peptides

“…Regardless of structural class (i.e., ␣-helix, ␤-sheet, loop, or extended), nonselective AMPs typically (i) are very hydrophobic, such that their interactions with membranes are governed primarily by the hydrophobic effect (10)(11)(12)(13)(14)(15), and (ii) have a well defined amphipathic structure (4,11,(14)(15)(16)(17). In contrast, the antibacterial activity of selective AMPs depends on (i) high net cationic charge (12)(13)(14)18) (although excessive cationic charge can also lead to hemolytic activity) (18, 19) and (ii) only moderate hydrophobicity (16,19,21,22). Perhaps counterintuitively, a well defined amphipathic structure is not necessary for selective antimicrobial activity (7,16); destabilization of AMP secondary structure often leads to improvements in selectivity (15,20).…”

“…In contrast, the antibacterial activity of selective AMPs depends on (i) high net cationic charge (12)(13)(14)18) (although excessive cationic charge can also lead to hemolytic activity) (18, 19) and (ii) only moderate hydrophobicity (16,19,21,22). Perhaps counterintuitively, a well defined amphipathic structure is not necessary for selective antimicrobial activity (7,16); destabilization of AMP secondary structure often leads to improvements in selectivity (15,20).…”

“…The precise nature of AMP-membrane interactions remains controversial and actively debated; a variety of mechanisms have been proposed, including the carpet (4), barrel-stave pore (4), toroidal pore (8), and aggregate (9) models. Nevertheless, a considerable number of structure-activity investigations have elucidated how the physicochemical properties of these molecules relate to their biological activities (4,7,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”

Antimalarial Activities of Dermaseptin S4 Derivatives

“…8A and B, respectively) demonstrates a remarkable parallelism in the way each modification affects both activities. Thus, S4 and all substitution derivatives are the most active, successive truncation of four residues from the C terminus leads to a gradual loss of activity, all N-terminal deletions result in inactivity except for S4(5-28), which retains partial activity, amidation of the C-terminal carboxyl increases potency of K 4 -S4 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), and successive C-terminal deletions of the substituted short derivatives gradually lead to inactivity.…”

“…Antimicrobial peptides are potentially active against a large spectrum of microorganisms, yet they are generally nontoxic to normal mammalian cells. The molecular basis for this selectivity is also ill defined, but it is believed to result from differences in the membrane fluidity and negative charge density in target microbial cells versus non-target cells, which result from differences in the lipid composition (3,4,11,12,14,16,31,42,46,53). Isomers composed of all D-amino acids display a potency identical to that of all the L counterparts, which implies that the mechanism of their antimicrobial activity is not mediated by interaction with specific receptors.…”