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Encyclopedia > Amyloid

Amyloids are insoluble fibrous protein aggregations sharing specific structural traits. The term amyloid may refer to the following: A blue to black chemical reaction to iodine in mycology - (amyloid (mycology)). A similar reaction and use in medicine for human or animal tissues - (amyloid). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...


Definition controversy

The name amyloid comes from the early mistaken identification of the substance as 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] Starch (CAS# 9005-25-8) is a complex carbohydrate which is insoluble in water; it is used by plants as a way to store excess glucose. ... For other uses, see Latin (disambiguation). ... A polyunsaturated triglyceride. ... Lactose is a disaccharide found in milk. ...

  • The classical, histopathological definition of amyloid is an extracellular, proteinaceous deposit exhibiting cross-beta structure. This is due to mis-folding of unstable proteins. Common to most cross-beta type structures they are generally identified by apple-green birefringence when stained with congo red and seen under polarized light. These deposits often recruit various sugars and other components such as Serum Amyloid P component, resulting in complex, and sometimes inhomogenous structures.[2] Recently this definition has come into question as some classic, amyloid species have been observed in distinctly intracellular locations.
  • A more recent, biophysical definition is broader, including any polypeptide which adopts a cross-beta polymerization, in vivo, or in vitro. Some of these, although demonstrably cross-beta sheet, fail other characteristic tests of amyloid, such as the congo red birefringence test. Microbiologists and biophysicists have largely adopted this definition, leading to some conflict in the biological community over an issue of language.

The remainder of this article will be inclusive with due deference to the controversy by indicating where amyloid species are observed only in the biophysical context. Histopathology is a field of pathology which specialises in the histologic study of diseased tissue. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Chemical structure of congo red Congo red is the sodium salt of benzidinedflandersiazo-bis-1-naphtylamine-4-sulfonic acid (formula: C32H22N6Na2O6S2; molecular weight: 696. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... Serum Amyloid P component (SAP) is the identical serum form of Amyloid P component (AP), a 25kDa pentameric protein first identified as the pentagonal constituent of in vivo pathological deposits called amyloid (Cathcart et al, 1967). ... In linguistics, prescription is the laying down or prescribing of normative rules for the use of a language, or the making of recommendations for effective language usage. ...

Diseases featuring amyloids

Transmissible spongiform encephalopathies (TSEs, also known as prion diseases) are a group of progressive conditions that affect the brain and nervous system of humans and animals and are transmitted by prions. ...

Non-disease amyloids

(mostly using the biophysical definition)

  • Native amyloids in organisms
    • Curli E. coli Protein (curlin)
    • Yeast Prions [Sup35] [3], Rnq1
    • Podospora Anserina Prion Het-s
    • Malarial coat protein
    • Spider silk (some but not all spiders)
    • Mammalian melanosomes (pMel)
    • Tissue-type plasminogen activator (tPA), a hemodynamic factor
  • Proteins and peptides known to make amyloid without any known disease
  • Proteins and peptides engineered to make amyloid

Binomial name Escherichia coli T. Escherich, 1885 Escherichia coli (usually abbreviated to E. coli) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of food. ... Malaria is a vector-borne infectious disease caused by protozoan parasites. ... Spider silk is a fibre secreted by spiders. ... Melanosome - Cellular A melanosome is a cellular organelle containing melanin, the commonest light-absorbing pigment found in the animal kingdom. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ...

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 fibres is by placing a sample in an X-ray diffraction beam; there are two characteristic scattering diffraction signals produced at 4.7 and 10 Ã…ngstroms (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. Diagram of β-pleated sheet with H-bonding between protein strands The β sheet (also β-pleated sheet) is the second form of regular secondary structure in proteins — the first is the alpha helix — consisting of beta strands connected laterally by three or more hydrogen bonds, forming a generally twisted, pleated sheet. ... In biochemistry, many proteins are actually assemblies of more than one protein (polypeptide) molecule, which in the context of the larger assemblage are known as protein subunits. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... An angstrom, angström, or Ã¥ngström (symbol Ã…) is a unit of length. ...

Amyloid polymerization is generally sequence-sensitive, that is, causing mutations in the sequence can prevent self-assembly, especially if the mutation is a beta-sheet breaker, such as proline. For example, humans produce an amyloidogenic peptide associated with type II diabetes, but, in Rodentia, a proline is substituted in a critical location and amyloidogenesis does not occur. A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... This article is about modern humans. ... Suborders Sciuromorpha Castorimorpha Myomorpha Anomaluromorpha Hystricomorpha Rodentia is an order of mammals also known as rodents. ...

There are two broad classes of amyloid-forming polypeptide sequences. Glutamine-rich polypeptides are important in the amyloidogenesis of Yeast and mammalian prions, as well as Huntington's disease. When peptides are in a beta-sheet conformation, particularly when the residues are parallel and in-register (causing alignment), glutamines can brace the structure by forming intrastrand hydrogen bonding between its amide carbonyls and nitrogens. In general, for this class of diseases, toxicity correlates with glutamine content. This has been observed in studies of onset age for Huntington's disease (the longer the polyglutamine sequence, the sooner the symptoms appear), and has been confirmed in a C. elegans model system with engineered polyglutamine peptides. For the bird called a prion, see Prion (bird) Prions - short for proteinaceous infectious particle - are infectious self-reproducing protein structures. ... Binomial name Caenorhabditis elegans Wild-type C. elegans hermaphrodite stained to highlight the nuclei of all cells Caenorhabditis elegans () is a free-living nematode (a roundworm), about 1 mm in length, which lives in a temperate soil environment. ...

Other polypeptides and proteins such as amylin and the Alzheimer's beta protein do not have a simple consensus sequence and are thought to operate by hydrophobic association. Among the hydrophobic residues, aromatic amino-acids are found to have the highest amyloidogenic propensity. Amylin, or Islet Amyloid Polypeptide (IAPP), is a 37-residue peptide hormone secreted by pancreatic β-cells at the same time as insulin (in a roughly 100:1 ratio). ...

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. A prion (IPA: [1] ) — short for proteinaceous infectious particle (-on by analogy to virion) — is a type of infectious agent composed only of protein. ...

Xu [4], using atomic force microscopy, has shown in both lysozyme and human tau40 that 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.

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 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 intiated by an underlying problem, such as one/some of the above mentioned side effects like calcium ion concentration imbalances.

Histological staining

Amyloid is typically identified by a change in the fluorescence intensity of planar aromatic dyes such as Thioflavin T or Congo Red. Congo red postitivity remains the gold standard for diagnosis of amyloidosis. This is generally attributed to the environmental change, as these dyes intercalate between beta-strands. Congophillic amyloid plaques generally cause apple-green birefringence, when viewed through crossed polarimetric filters. To avoid nonspecific staining, histology stains, such as haematoxylin and eosin stain, are used to quench the dyes' activity in other places where the dye might bind, such as the nucleus. The dawn of antibody technology and immunohistochemistry has made specific staining easier, but often this can cause trouble because epitopes can be concealed in the amyloid fold; an amyloid protein structure is generally a different conformation from that which the antibody recognizes. Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. ... Look up dye in Wiktionary, the free dictionary. ... Thioflavin T mw: 318. ... Chemical structure of congo red Congo red is the sodium salt of benzidinedflandersiazo-bis-1-naphtylamine-4-sulfonic acid (formula: C32H22N6Na2O6S2; molecular weight: 696. ... A thin section of lung tissue stained with hematoxylin and eosin. ... Haematein Haematoxylin, hematoxylin, Natural Black 1, or C.I. 75290 is extracted from the wood of the logwood tree. ... Eosin is an orange-pink dye derived from coal tar. ... Immunohistochemistry or IHC refers to the process of localizing proteins in cells of a tissue section exploiting the principle of antibodies binding specifically to antigens in biological tissues. ...

See also

A prion (IPA: [1] ) — short for proteinaceous infectious particle (-on by analogy to virion) — is a type of infectious agent composed only of protein. ... Proteopathy (Proteo- [pref. ...


  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

External links

  • Amyloid Precursor Protein, CTF fragments at rpeptide.com
  • Amyloid Treatment and Research Program at Boston University
  • Amyloid: Journal of Protein Folding Disorders web page at tandf.co.uk
  • Amyloidosis web page at Cornell University
  • Information, support and advice to anyone with Amyloidosis, particularly in Australia (www.amyloidosisaustralia.org)
  • Amyloidosis Support Network at amyloidosis.org
  • UK National Amyloidosis Centre - one of the largest amyloid diagnosis and research centres at ucl.ac.uk
  • Engineering Amyloid for material at University of California, Berkeley
  • Amyloidosis Research Foundation amyloidosisresearchfoundation.org
  • National Kidney and Urologic Diseases Information Clearinghouse at National Institute of Health
  • Eubanks L, Rogers C, Beuscher A, Koob G, Olson A, Dickerson T, Janda K (2006). "A molecular link between the active component of marijuana and Alzheimer's disease pathology". Mol. Pharm. 3 (6): 773-7. PMID 17140265. 

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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, rather a deposition of proteinaceous mass.
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