A current hypothesis for the pathology of Alzheimer's disease (AD) proposes that amyloid-beta (A[beta]) peptides induce uncontrolled, neurotoxic ion flux across cellular membranes. The resulting inability of neurons to regulate their intracellular concentration of ions, in particular calcium ions, has been associated with cell death and may thus contribute to cognitive impairment typical for AD. The mechanism of the ion flux is not fully understood since no experimentally based A[beta] channel structures at atomic resolution are currently available, and few polymorphisms have been predicted by computational models. Structural models and experimental evidence suggest that A[beta] channel is an assembly of loosely-associated mobile [beta]-sheet subunits. Using planar lipid bilayers, we present a study showing that amino acidic substitutions can be used to infer which residues are essential for channel structure and/or line the pore. We tested: A[beta]42-F19P, A[beta]42-F20C, A[beta]42-A42C, and A[beta]42-D1C. The substitution of F19P inhibited channel formation. All the cysteine mutants tested are capable of forming channels, but with different characteristics. This and other structural information on or in membrane are needed to aid the understanding of channel formation and structure. Additionally, this information should aid studies of drug design aiming to control unregulated A[beta] ion fluxes

Alzheimer's disease (AD) is the most common type of senile dementia in aging populations. Amyloid β (Aβ)-mediated dysregulation of ionic homeostasis is the prevailing underlying mechanism leading to synaptic degeneration and neuronal death. Aβ-dependent ionic dysregulation most likely occurs either directly via unregulated ionic transport through the membrane or indirectly via Aβ binding to cell membrane receptors and subsequent opening of existing ion channels or transporters. Receptor binding is expected to involve a high degree of stereospecificity. Here, we investigated whether an Aβ peptide enantiomer, whose entire sequence consists of d-amino acids, can form ion-conducting channels; these channels can directly mediate Aβ effects even in the absence of receptor-peptide interactions. Using complementary approaches of planar lipid bilayer (PLB) electrophysiological recordings and molecular dynamics (MD) simulations, we show that the d-Aβ isomer exhibits ion conductance behavior in the bilayer indistinguishable from that described earlier for the l-Aβ isomer. The d isomer forms channel-like pores with heterogeneous ionic conductance similar to the l-Aβ isomer channels, and the d-isomer channel conductance is blocked by Zn(2+), a known blocker of l-Aβ isomer channels. MD simulations further verify formation of β-barrel-like Aβ channels with d- and l-isomers, illustrating that both d- and l-Aβ barrels can conduct cations. The calculated values of the single-channel conductance are approximately in the range of the experimental values. These findings are in agreement with amyloids forming Ca(2+) leaking, unregulated channels in AD, and suggest that Aβ toxicity is mediated through a receptor-independent, nonstereoselective mechanism.