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Aurein 2.5 (GLFDIVKKVVGAFGSL-NH(2)) is an amphibian antimicrobial peptide. Here, characterisation studies showed the peptide to exhibit molecular areas at an air / water interface (1.77 - 3.1 nm(2)), which are in agreement with the adoption of alpha-helical structures. Lipid monolayer studies showed aurein 2.5 to induce maximal surface pressure changes of circa 7 mN m(-1) in monolayers formed from phosphatidylglycerol (PG) and circa 6 mN m(-1) in those formed from phosphatidylethanolamine (PE). These data indicate that the membrane interactions of the peptide are amphiphilicity driven with no apparent electrostatic requirement. Individually mutating the phenylalanine residues of aurein 2.5 to leucine had no major effect on the levels of PG and PE interactions, suggesting that these residues are not essential to the membrane interactions of the peptide, contrasting to other aureins where corresponding phenylalanine residues are required for efficient membrane interaction and antibacterial activity. This difference in the requirement is suggested to relate to the surface architecture as proposed by the concept of the molecular perturbation potential.

Here, it is shown that amphiphilicity profiling based on the mean hydrophobic moment provides a simple visual guide for the identification of oblique orientated a-helices. The methodology has an efficiency of circa 70% and predicts that approximately 40% of transmembrane a-helices may possess these structures.

To facilitate microbial membrane invasion, amphiphilic α-helical antimicrobial peptides (α-AMPs) show a spatial segregation of hydrophobic and hydrophilic residues about the α-helical long axis. Here we discuss potential mechanisms by which these peptides are able to disrupt membrane structure and the structural characteristics, which are required for function.

A database of alpha-helical antimicrobial peptides (AMP) was established and their minimum inhibitory concentrations (MIC) were compared with their physiochemical characteristics in an attempt to establish those features that determine efficacy. There is no significant difference in AMP sensitivity between Gram-positive and Gram-negative bacteria but fungi did require higher concentrations to achieve the same degree of growth inhibition. For antibacterial peptides there appears to be a positive correlation between MIC and hydrophobic arc size and a negative correlation between MIC and net charge.

Oblique orientated α-helices are highly specialised protein structural elements that penetrate membranes at a shallow angle and are used to promote membrane destabilisation by a number of protein classes. Here, the use of extended hydrophobic moment methodology shows that the amphibian extrudates, aurein 1.2 and citropin 1.1, may use oblique orientated α-helices in their antimicrobial action and that such use may be shared by other antimicrobial peptides. This appears to be the first systematic analysis of these peptides for the possession of oblique orientated a-helical structure.