Metals are found associated with β-pleated sheets of Aβ42 in vivo and may be involved in their formation. Metal chelation has been proposed as a therapy for Alzheimer's disease on the basis that it may safely dissolve precipitated Aβ peptides. We have followed fibrillisation of Aβ42 in the presence of an additional metal ion (Al(III), Fe(III), Zn(II), Cu(II)) over a period of 32 weeks and we have investigated the dissolution of these aged peptide aggregates in the presence of both desferrioxamine (DFO) and ethylenediaminetetraacetic acid (EDTA). Aβ42 either alone or in the presence of Al(III) or Fe(III) formed β-pleated sheets of plaque-like amyloids which were dissolved upon incubation with either chelator. Zn(II) inhibited whilst Cu(II) prevented the formation of β-pleated sheets of Aβ42 and neither of these influences were affected by incubation of the aged peptide aggregates with either DFO or EDTA. Freshly prepared solutions of Aβ42 either alone or in the presence of added Al(III) or Fe(III) did not form β-pleated amyloid in the presence of DFO when incubated for up to 8 weeks. EDTA did not prevent β-pleated amyloid formation in the same treatments and promoted β-pleated amyloid formation in the presence of either Zn(II) or Cu(II). The presence of significant concentrations of Al(III) and Fe(III) as contaminants of 'Aβ42 only' preparations suggested that both of these metals were involved in either triggering the formation or stabilising the structure of β-pleated amyloid. If the formation of such amyloid is critical to the aetiology of AD then the chelation of Al(III) and Fe(III) may prove to be a protective mechanism whilst the chelation of Cu(II) and Zn(II) without also chelating Al(III) and Fe(III) might actually exacerbate the condition.

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Bacteria have developed several evolutionary strategies to protect their cell membranes (CMs) from the attack of antibiotics and antimicrobial peptides (AMPs) produced by the innate immune system, including remodeling of phospholipid content and localization. Multidrug-resistantEnterococcus faecalis,an opportunistic human pathogen, evolves resistance to the lipopeptide daptomycin and AMPs by diverting the antibiotic away from critical septal targets using CM anionic phospholipid redistribution. The LiaFSR stress response system regulates this CM remodeling via the LiaR response regulator by a previously unknown mechanism. Here, we characterize a LiaR-regulated protein, LiaX, that senses daptomycin or AMPs and triggers protective CM remodeling. LiaX is surface exposed, and in daptomycin-resistant clinical strains, both LiaX and the N-terminal domain alone are released into the extracellular milieu. The N-terminal domain of LiaX binds daptomycin and AMPs (such as human LL-37) and functions as an extracellular sentinel that activates the cell envelope stress response. The C-terminal domain of LiaX plays a role in inhibiting the LiaFSR system, and when this domain is absent, it leads to activation of anionic phospholipid redistribution. Strains that exhibit LiaX-mediated CM remodeling and AMP resistance show enhanced virulence in theCaenorhabditis elegansmodel, an effect that is abolished in animals lacking an innate immune pathway crucial for producing AMPs. In conclusion, we report a mechanism of antibiotic and AMP resistance that couples bacterial stress sensing to major changes in CM architecture, ultimately also affecting host–pathogen interactions.

Unbiased molecular simulation is a powerful tool to study the atomic details driving functional structural changes or folding pathways of highly fluid systems, which present great challenges experimentally. Here we apply unbiased long-timescale molecular dynamics simulation to study the ab initio folding and partitioning of melittin, a template amphiphilic membrane active peptide. The simulations reveal that the peptide binds strongly to the lipid bilayer in an unstructured configuration. Interfacial folding results in a localized bilayer deformation. Akin to purely hydrophobic transmembrane segments the surface bound native helical conformer is highly resistant against thermal denaturation. Circular dichroism spectroscopy experiments confirm the strong binding and thermostability of the peptide. The study highlights the utility of molecular dynamics simulations for studying transient mechanisms in fluid lipid bilayer systems. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.