Structural and functional characterization of unmodified and pyroglutamylated amyloid beta peptides in lipid bilayers

The amyloid β (Aβ) peptide forms soluble oligomers, which play a key role in the etiology of Alzheimer’s disease (AD). N-terminal truncation and pyroglutamylation of Aβ significantly affects its biophysical/biochemical properties and enhances cytotoxicity. One of the mechanisms of neurotoxicity of Aβ is membrane destabilization or pore formation and dysregulation of cellular ionic homeostasis. Here, the structural features and ion-conducting channel formation in lipid bilayers by four Aβ variants (Aβ_1-42, Aβ_1-40, Aβ_pE3-42, Aβ_pE3-40) are reported. Voltage clamp bilayer electrophysiology studies indicate that all variants exhibit ion channel activity in phosphatidylcholine/phosphatidylglycerol/cholesterol (6:3:1 mol%) bilayers with distinct conductance behaviors. Aβ_1-42 and Aβ_pE3-42 show step-like conductance changes with well-defined open-close states whereas Aβ_1-40 and Aβ_pE3-40 show high-frequency burst-like activity with multi-state conductance. Structural data from circular dichroism and infrared spectroscopy identify significant β-sheet content for the peptides in lipid membranes. In all cases, the channel activity could be blocked by Zn²⁺ ions to varying degrees. Overall, these results suggest that pyroglutamylated variants of Aβ, like unmodified Aβ, are capable of forming ion channels in cell membranes. Characterization of the molecular structure and ion channel formation activities of the most abundant and toxic Aβ species may help in rational drug design for AD.