Structure‐Activity Analyses of β‐Amyloid Peptides: Contributions of the β25–35 Region to Aggregation and Neurotoxicity

TLDR

Alzheimer’s disease neurodegeneration is thought to be driven by insoluble β‑amyloid plaques, with in‑vitro neurotoxicity linked to the peptide’s aggregated conformation. The study aims to analyze how modifications of β‑amyloid peptides, particularly the β25–35 fragment and full‑length β1–42, affect aggregation and neurotoxicity. The authors used systematic deletions and substitutions of residues in β‑amyloid peptides to assess their capacity to form sedimentable aggregates and to induce toxicity in cultured hippocampal neurons. The analyses revealed that aggregation and neurotoxicity are tightly linked, with the β33–35 region of β25–35 being essential for both, while full‑length β1–42 aggregation disruption is evident from altered electrophoretic profiles, fibril morphology, and loss of β‑sheet CD signatures, thereby delineating the structural determinants of β‑amyloid toxicity.

Abstract

Abstract: The neurodegeneration of Alzheimer's disease has been theorized to be mediated, at least in part, by insoluble aggregates of β‐amyloid protein that are widely distributed in the form of plaques throughout brain regions affected by the disease. Previous studies by our laboratory and others have demonstrated that the neurotoxicity of β‐amyloid in vitro is dependent upon its spontaneous adoption of an aggregated structure. In this study, we report extensive structure‐activity analyses of a series of peptides derived from both the proposed active fragment of β‐amyloid, β25–35, and the full‐length protein, β1–42. We examine the effects of amino acid residue deletions and substitutions on the ability of β‐amyloid peptides to both form sedimentable aggregates and induce toxicity in cultured hippocampal neurons. We observe that significant levels of peptide aggregation are always associated with significant β‐amyloid‐induced neurotoxicity. Further, both N‐ and C‐terminal regions of β25–35 appear to contribute to these processes. In particular, significant disruption of peptide aggregation and toxicity result from alterations in the β33–35 region. In β1–42 peptides, aggregation disruption is evidenced by changes in both electrophoresis profiles and fibril morphology visualized at the light and electron microscope levels. Using circular dichroism analysis in a subset of peptides, we observed classic features of β‐sheet secondary structure in aggregating, toxic β‐amyloid peptides but not in nonaggregating, nontoxic β‐amyloid peptides. Together, these data further define the primary and secondary structures of β‐amyloid that are involved in its in vitro assembly into neurotoxic peptide aggregates and may underlie both its pathological deposition and subsequent degenerative effects in Alzheimer's disease.