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

Biochemistry. 2022 Feb 15;61(4):252-264. doi: 10.1021/acs.biochem.1c00739. Epub 2022 Jan 26.

Abstract

Aβ dimers are a basic building block of many larger Aβ oligomers and are among the most neurotoxic and pathologically relevant species in Alzheimer's disease. Homogeneous Aβ dimers are difficult to prepare, characterize, and study because Aβ forms heterogeneous mixtures of oligomers that vary in size and can rapidly aggregate into more stable fibrils. This paper introduces AβC18C33 as a disulfide-stabilized analogue of Aβ42 that forms stable homogeneous dimers in lipid environments but does not aggregate to form insoluble fibrils. The AβC18C33 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 AβC18C33 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) spectroscopy establishes that AβC18C33 adopts a β-sheet conformation in detergent solutions and supports a model in which the intramolecular disulfide bond induces β-hairpin folding and dimer formation in lipid environments. Thioflavin T (ThT) fluorescence assays and transmission electron microscopy (TEM) studies indicate that AβC18C33 does not undergo fibril formation in aqueous buffer solutions and demonstrate that the intramolecular disulfide bond prevents fibril formation. The recently published NMR structure of an Aβ42 tetramer (PDB: 6RHY) provides a working model for the AβC18C33 dimer, in which two β-hairpins assemble through hydrogen bonding to form a four-stranded antiparallel β-sheet. It is anticipated that AβC18C33 will serve as a stable, nonfibrilizing, and noncovalent Aβ dimer model for amyloid and Alzheimer's disease research.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alzheimer Disease / metabolism*
  • Amyloid / chemistry
  • Amyloid / metabolism*
  • Amyloid beta-Peptides / chemistry
  • Amyloid beta-Peptides / metabolism*
  • Circular Dichroism / methods
  • Disulfides / chemistry
  • Disulfides / metabolism*
  • Humans
  • Hydrogen Bonding
  • Microscopy, Electron, Transmission / methods
  • Models, Molecular
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Protein Conformation
  • Protein Conformation, beta-Strand

Substances

  • Amyloid
  • Amyloid beta-Peptides
  • Disulfides
  • Peptide Fragments
  • amyloid beta-protein (40-42)