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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Amyloids are insoluble fibrous protein aggregations sharing specific structural traits.

Definition Controversy

  • The name amyloid comes from the early mistaken identification of the substance "starch" (amylum in Latin), based on crude iodine-staining techniques. For a period, the scientific community debated whether or not amyloid deposits were fatty deposits or carbohydrate deposits until it was finally resolved that it was neither, but rather a deposition of proteinaceous mass.[1]

Diseases Featuring Amyloids

Non-Disease Amyloids

(Mostly using the biophysical definition)

Amyloid Biophysics

  • Amyloid is characterized by a cross-beta sheet quaternary structure; that is, the strands come from different monomers and align perpendicular to the axis of the fibril. While amyloid is usually identified using fluorescent dyes, stain polarimetry, circular dichroism, or FTIR (all indirect measurements), the gold standard test to see if a structure contains cross-beta fibers is by placing a sample in an x-ray diffraction beam; there are two characteristic scattering diffraction signals produced at 4.7 and 10 Ångstroms (0.47 nm and 1.0 nm), corresponding to the interstrand and stacking distances in beta sheets. It should be noted that the "stacks" of beta sheet are short and traverse the breadth of the amyloid fibril; the length of the amyloid fibril is built by aligned strands.
  • For these peptides, cross-polymerization (fibrils of one polypeptide sequence causing other fibrils of another sequence to form) is a phenomenon observed in vitro. This phenomenon is important since it would explain interspecies prion propagation and amyloid biophysics differential rates of propagation, as well as a statistical link between Alzheimer's and diabetes. In general, cross-polymerization is more efficient the more similar the peptide sequence, though entirely dissimilar sequences can cross-polymerize and highly similar sequences can even be "blockers" which prevent polymerization. Polypeptides will not cross-polymerize their mirror-image counterparts, indicating that the phenomenon involves specific binding and recognition events.
  • Xu, using atomic force microscopy, has shown in both lysozyme and human tau40, the formation of amyloid fibers is a two-step process in which proteins first aggregate into uniform colloidal spheres of ~20nm diameter. The spheres then join to form characteristic linear chains, which evolve over time into mature amyloid fibers. He proposes that aggregation drives conformational change and that a conformational change is not essential to initiate the aggregation process.[4]

Amyloid Pathology

  • The reasons for amyloid association with disease is unclear. In many cases, the deposits physically disrupt tissue architecture, suggesting disruption of function by some bulk process.
  • In other cases, cell death is believed to precede amyloid deposition, suggesting that small amyloid-like oligomers (possibly but not necessarily biophysically amyloid) cause cell death. There is significant speculation that amyloid fibrils can also puncture cells or cause problems such as ionic imbalance in cells.
  • Further speculation has led to the hypothesis that while amyloid association may be the cause of health issues, the association itself is initiated by an underlying problem, such as one/some of the above mentioned side effects like calcium ion concentration imbalances.
  • For more information on the deposition of amyloid protein in the body (amyloidosis), click here.

Histological Staining

See also


  1. Kyle, R.A. (2001) Amyloidosis: a convoluted story. Brit. J. Haem. 114:529-538. PMID 11552976
  2. Sipe, J. D. and Cohen, A.S. (2000) Review: History of the Amyloid Fibril. J. Struct. Biol. 130:88-98. PMID 10940217
  3. Nakayashiki, PNAS, 2005
  4. Xu S. Aggregation drives "misfolding" in protein amyloid fiber formation. Amyloid 2007 Jun;14(2):119-31. PMID 17577685

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