A Disulfide-Stabilized Aβ that Forms Dimers but Does Not Form Fibrils

A beta dimers are a basic building block of many larger A beta oligomers and are among the most neurotoxic and pathologically relevant species in Alzheimer's disease. Homogeneous A beta dimers are difficult to prepare, characterize, and study because A beta forms heterogeneous mixtures of oligomers that vary in size and can rapidly aggregate into more stable fibrils. This paper introduces A beta(C18C33) as a disulfide-stabilized analogue of A beta(42) that forms stable homogeneous dimers in lipid environments but does not aggregate to form insoluble fibrils. The A beta(C18C33) peptide is readily expressed in Escherichia coli and purified by reverse-phase HPLC to give ca. 8 mg of pure peptide per liter of bacterial culture. SDS-PAGE establishes that A beta(C18C33) forms homogeneous dimers in the membrane-like environment of SDS and that conformational stabilization of the peptide with a disulfide bond prevents the formation of heterogeneous mixtures of oligomers. Mass spectrometric (MS) studies in the presence of dodecyl maltoside (DDM) further confirm the formation of stable noncovalent dimers. Circular dichroism (CD) (C18C33) adopts a beta-sheet conformation in detergent solutions and supports a model in which the intramolecular disulfide bond induces beta-hairpin folding and dimer formation in lipid environments. Thioflavin T (ThT) fluorescence assays and transmission electron microscopy (TEM) studies indicate that A beta buffer solutions and demonstrate that the intramolecular disulfide bond prevents fibril formation. The recently published NMR structure of an A beta(42) tetramer (PDB: 6RHY) provides a working model for the A beta (C18C33) dimer, in which two beta-hairpins assemble through hydrogen bonding to form a four-stranded antiparallel beta-sheet. It is anticipated that A beta(C18C33) will serve as a stable, nonfibrilizing, and noncovalent A beta dimer model for amyloid and Alzheimer's disease research.

Automated summary

A beta dimers are neurotoxic and pathologically relevant species in Alzheimer's disease. This paper introduces a stable A beta(C18C33) dimer model that forms pure dimers in lipid environments without aggregation into fibrils. This model is important for amyloid and Alzheimer's disease research.