Aurein 1.2 is a 13 residue antimicrobial peptide secreted by the Australian tree frog Litoria Aurea. It is a surface-acting membrane disrupting peptide that permeabilizes bacterial membranes via the carpet mechanism; the molecular details of this process are mostly unknown. Here the mechanism of action of Aurein 1.2 was investigated with an emphasis on the role of membrane charge and C-terminal amidation of the peptide. Using quartz crystal microbalance (QCM) fingerprinting it was found that the membrane charge correlates with membrane affinity of the peptide, however the binding and the membrane disrupting processes are not charge driven; increased membrane charge reduces the membrane disrupting activity. Coarse grain simulations revealed that phenylalanine residues act as membrane anchors. Accordingly Aurein 1.2 has the ability to bind to any membrane. Furthermore, bundling precludes membrane disruption in case of wild type peptides, while non C-terminal amidated peptides form random aggregates leading to detachment from the membrane. Hence C-terminal amidation is crucial for Aurein 1.2 action. Our results suggest that Aurein 1.2 acts via aggregation driven membrane penetration. The concomitant change in the tension of the outer leaflet imposes a spontaneous curvature on the membrane, leading to disintegration.

Membrane-disrupting antimicrobial peptides provide broad-spectrum defence against localized bacterial invasion in a range of hosts including humans. The most generally held consensus is that targeting to pathogens is based on interactions with the head groups of membrane lipids. Here we show that the action of LL-37, a human antimicrobial peptide switches the mode of action based on the structure of the alkyl chains, and not the head groups of the membrane forming lipids. We demonstrate that LL-37 exhibits two distinct interaction pathways: pore formation in bilayers of unsaturated phospholipids and membrane modulation with saturated phospholipids. Uniquely, the membrane modulation yields helical-rich fibrous peptide-lipid superstructures. Our results point at alternative design strategies for peptide antimicrobials.

Copper oxide (CuO) nanosheets synthesized in polyvinylpyrrolidone (PVP) were characterized with respect to antimicrobial activity by quick precipitation method. Different sizes and shapes of CuO nanosheets were obtained by simple variations of PVP concentrations. The x-ray diffraction results revealed the formation of pure-phase CuO with monoclinic structure. Transmission electron microscopy analysis showed that the average ratio of length to width of these nanosheets increased with increasing PVP concentrations. Due to the quantum size effect, CuO nanosheets exhibit a blue shift in the ultraviolet-visible spectra. Field emission scanning electron microscopy results showed that as the concentration of PVP increased, well-defined morphologies were formed on the surface of the products. Energy dispersive analysis of x-ray clearly confirmed the presence of Cu and O with an atomic ratio of 1:1. Fourier transform infrared spectroscopy results showed that C5O in PVP coordinated with CuO and formed a protective layer. The mechanism of the reaction was also discussed. CuO nanosheets in suspension showed activity against a range of bacterial pathogens and fungi with minimum bactericidal concentrations (MBCs) ranging from 100 to 5000 lg/mL. The extent of the inhibition zones and the MBCs was found to be size-dependent.

Caenorhabditis elegans are typically cultured in a monoxenic medium consisting of live bacteria. However, this introduces a secondary organism to experiments, and restricts the manipulation of the nutritional environment. Due to the intricate link between genes and environment, greater control and understanding of nutritional factors are required to push the C. elegans field into new areas. For decades, attempts to develop a chemically defined, axenic medium as an alternative for culturing C. elegans have been made. However, the mechanism by which the filter feeder C. elegans obtains nutrients from these liquid media is not known. Using a fluorescence-activated cell sorting based approach, we demonstrate growth in all past axenic C. elegans media to be dependent on the presence of previously unknown particles. This particle requirement of C. elegans led to development of liposome-based, nanoparticle culturing that allows full control of nutrients delivered to C. elegans.

Aurein 1.2 is a small cationic antimicrobial peptide, one of the shortest peptides that can exert antimicrobial activity at low micromolar concentrations. Aurein 1.2 is a surface acting peptide, following the "carpet" mechanism of thresholded membrane disruption. It is generally assumed that the activity of such cationic α-helical membrane disrupting peptides is charge driven. Here, the authors show that instead of charge interactions, aromatic phenylalanine residues of the Aurein 1.2 sequence facilitate the membrane binding. The activity of the wild type peptide was compared to mutants in which the Phe residues were substituted, singly and in tandem, with alanine. Measurements by quartz crystal microbalance, impedance spectroscopy, and dye leakage experiments demonstrated that single residue mutants retain a much-reduced activity whereas the deletion of both Phe residues prevents membrane disruption entirely. The single residue mutants exhibited an altered mechanism of action, permeabilizing but not dissolving the target membranes. These results offer a new design rule for membrane disrupting peptides with potential pharmacological applications.