Amyloid

Amyloid is an ordered protein aggregate whose molecules form fibrils rich in cross-β-sheet structure. Amyloids occur in many diseases and also serve normal biological functions.

Cross-β structure: A protein architecture in which β-strands run roughly perpendicular to a fibril’s long axis, forming stacked β-sheets. This repeating arrangement gives amyloid fibrils their characteristic structural signature.
Protein folding: The process by which a protein adopts a three-dimensional structure determined by its sequence and environment. Amyloid assembly competes with the folding routes that produce soluble protein structures.
Alzheimer's disease: A progressive neurodegenerative disorder associated with cognitive decline and characteristic brain pathology. Amyloid-β deposits are a defining pathological feature, though they do not alone explain the disease.
Inclusion body: An abnormal intracellular accumulation of proteins or other materials visible in cells. Many inclusions contain aggregated protein, but an inclusion is not necessarily amyloid.
Amyloid oligomer: A small assembly of amyloid-forming protein molecules that exists before or alongside mature fibrils. Which oligomer structures are toxic, and how they cause damage, remain active research questions.
Protein misfolding: The adoption of a protein structure that differs from its functional native state. Misfolded conformations can expose surfaces that promote amyloid assembly.
Beta sheet: A protein secondary structure formed by hydrogen-bonded, extended polypeptide strands. Amyloid fibrils build their cross-β architecture from β-sheet interactions.
Systemic amyloidosis: A group of disorders in which amyloid deposits accumulate in organs or tissues beyond the central nervous system. These diseases show how amyloid deposition can damage many different organs.
Amorphous protein aggregate: A disordered cluster of aggregated proteins lacking the regular fibrillar architecture of amyloid. Amyloid is distinguished by ordered cross-β fibrils rather than aggregation alone.
Amyloid cascade hypothesis: A hypothesis that amyloid-β accumulation initiates a chain of events leading to Alzheimer's disease pathology. Clinical and experimental findings continue to test how directly amyloid-β drives disease.

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