Detailed Explanation
Amyloids are abnormal fibrillar aggregates formed when peptides or proteins misfold and stack into highly ordered structures called cross-β sheets. In this arrangement, individual peptide strands run perpendicular to the fiber axis and are held together by extensive hydrogen bonding between backbone atoms. The resulting fibrils are extraordinarily stable — resistant to proteases, detergents, and heat.
Amyloid formation is implicated in over 50 diseases. In Alzheimer's disease, the amyloid-β peptide (Aβ, 40–42 amino acids cleaved from amyloid precursor protein) aggregates into plaques in the brain. In type 2 diabetes, the 37-amino-acid islet amyloid polypeptide (IAPP/amylin) forms deposits in pancreatic islets. In Parkinson's disease, α-synuclein (140 amino acids) forms amyloid fibrils in neurons.
Not all amyloids are pathological. Functional amyloids exist in bacteria (curli fibers for biofilm formation), in humans (Pmel17 for melanin biosynthesis), and in hormone storage (peptide hormones are stored as amyloid-like aggregates in secretory granules). Understanding the distinction between toxic and functional amyloid is an active area of research.
Key Facts
- Cross-β sheet structure: strands perpendicular to fiber axis
- Implicated in 50+ diseases including Alzheimer's, Parkinson's, type 2 diabetes
- Extremely stable: resists proteases, detergents, heat
- Functional amyloids also exist (biofilm, melanin synthesis, hormone storage)
- Aβ peptide (40–42 aa) is the Alzheimer's amyloid
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