Amyloid peptides are a class of misfolded proteins that aggregate into insoluble fibrils, playing a central role in neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and systemic amyloidosis. Despite decades of research, the mechanisms underlying amyloid toxicity remain incompletely understood. 

Amyloid peptides are short protein fragments that self-assemble into β-sheet-rich fibrils, forming amyloid plaques in tissues. The most studied amyloid peptide, amyloid-β (Aβ), is implicated in Alzheimer's disease, while others, such as α-synuclein and islet amyloid polypeptide (IAPP), are linked to Parkinson's disease and type 2 diabetes, respectively. These peptides share a common structural motif but exhibit distinct pathological mechanisms, making them challenging therapeutic targets.

Structural Properties of Amyloid Peptides

Amyloid peptides have distinct structural features that contribute to their aggregation and toxicity:

• Primary Structure: Amyloid peptides are typically 20–40 amino acids long, with hydrophobic regions that promote aggregation. For example, Aβ peptides (e.g., Aβ40 and Aβ42) are derived from the amyloid precursor protein (APP) via proteolytic cleavage.
• Secondary Structure: Amyloid peptides adopt a β-sheet conformation, enabling the formation of cross-β structures that stack into fibrils.
• Tertiary and Quaternary Structure: Fibrils are stabilized by hydrogen bonds and hydrophobic interactions, forming highly ordered, insoluble aggregates.

Pathogenesis of Amyloid Peptides

Amyloid peptides contribute to disease through various mechanisms:

• Neurotoxicity:
  • Aβ Peptides: Aβ oligomers disrupt synaptic function, induce oxidative stress, and trigger neuroinflammation, leading to neuronal death.
  • α-Synuclein: Aggregates of α-synuclein form Lewy bodies, impairing dopamine signaling and contributing to PD pathology.
• Systemic Effects:
  • IAPP: Aggregated IAPP damages pancreatic β-cells, contributing to insulin deficiency in type 2 diabetes.
• Prion-like Propagation: Amyloid aggregates can spread between cells in a prion-like manner, propagating pathology across tissues.