| Revision as of 02:14, 13 December 2004 editGene Nygaard (talk | contribs)Extended confirmed users90,047 editsm →Amyloid biophysics: link and conversion← Previous edit | Revision as of 11:56, 13 December 2004 edit undoJfdwolff (talk | contribs)Administrators81,547 edits fmt, moved external link to appropriate section (we really need a seperate clinical page on the amyloidoses)Next edit → | ||
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| '''Amyloid''' describes various types of ] aggregations that share specific traits when examined ]. The name ''amyloid'' comes from the early mistaken identification of the substance as ] |
'''Amyloid''' describes various types of ] aggregations that share specific traits when examined ]. The name ''amyloid'' comes from the early mistaken identification of the substance as ] (''amylum'' in ]), based on crude iodine-staining techniques. For a period the scientific community debated whether or not amyloid deposits were ] deposits or ] deposits until it was finally resolved that it was neither, rather a deposition of proteinaceous mass. | ||
| The phenotypes of genetically transmitted amyloid diseases are often inherited in an ] fashion; (] is in fact in most genetics texts the canonical autosomal dominant disease). Sometimes the difference between aggressive amyloid diseases and senescent amyloid diseases is |
The phenotypes of genetically transmitted amyloid diseases are often inherited in an ] fashion; (] is in fact in most genetics texts the canonical autosomal dominant disease). Sometimes, the difference between aggressive amyloid diseases and senescent amyloid diseases is due to a mutation which makes the protein more prone to aggregation. Most commonly seen are point mutations which affect the cohesiveness of the protein and promote misfolding; other mutations cause aggregation-prone pieces of the protein to be cleaved off from the rest of the protein. | ||
| ==Diseases |
==Diseases featuring amyloid== | ||
| It should be noted that in almost all of the organ-specific pathologies, there is significant debate as to whether the amyloid plaques are the causal agent of the disease or if they are instead a symptom downstream of a common ideopathic agent. The associated proteins are indicated in parentheses. | It should be noted that in almost all of the organ-specific pathologies, there is significant debate as to whether the amyloid plaques are the causal agent of the disease or if they are instead a symptom downstream of a common ideopathic agent. The associated proteins are indicated in parentheses. | ||
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| *** Mutations in ], ], ], ] | *** Mutations in ], ], ], ] | ||
| ** Secondary amyloidosis | ** Secondary amyloidosis | ||
| *** ''AA amyloidosis'' (] |
*** ''AA amyloidosis'' (amyloid A protein, an ] due to chronic ]) | ||
| *** ''AL amyloidosis'' (] light chains) | *** ''AL amyloidosis'' (] light chains) | ||
| *** ''Gelsolin |
*** ''Gelsolin amyloidosis'' (plasma gelsolin fragments). | ||
| * Organ-specific amyloidosis | * Organ-specific amyloidosis | ||
| ** ] (amylin |
** ] (amylin, also known as IAPP) | ||
| ** ] | ** ] | ||
| *** ] (a<math>\beta</math> 1-40) | *** ] (a<math>\beta</math> 1-40) | ||
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| ** ]l coat protein | ** ]l coat protein | ||
| ** ] | ** ] | ||
| ⚫ | * | ||
| ⚫ | ==Histological staining |
||
| ⚫ | Amyloid is typically identified by a change in the fluorescence intensity of planar aromatic dyes such as Thioflavin T or ]. This is generally attributed to the environmental change as these dyes intercolate between beta-strands. Congophillic amyloid plaques generally cause apple-green birefringence, when viewed through crossed polarimetric filters. To avoid nonspecific staining ] stains such as ] 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 ] 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. | ||
| ==Amyloid biophysics== | ==Amyloid biophysics== | ||
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| 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. Cross-polymerization is a phenomenon observed in vitro, and this is a putative mechanism explaining a link between diabetes and Alzheimer's disease. This is also the mechanism of ] propagation. | 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. Cross-polymerization is a phenomenon observed in vitro, and this is a putative mechanism explaining a link between diabetes and Alzheimer's disease. This is also the mechanism of ] propagation. | ||
| ⚫ | ==Histological staining== | ||
| ⚫ | Amyloid is typically identified by a change in the fluorescence intensity of planar aromatic dyes such as Thioflavin T or ]. This is generally attributed to the environmental change as these dyes intercolate between beta-strands. Congophillic amyloid plaques generally cause apple-green birefringence, when viewed through crossed polarimetric filters. To avoid nonspecific staining ] stains such as ] 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 ] 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. | ||
| ==External links== | ==External links== | ||
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| * | * | ||
| * (research institute) | * (research institute) | ||
| ⚫ | * | ||
Revision as of 11:56, 13 December 2004
Amyloid describes various types of protein aggregations that share specific traits when examined microscopically. 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, rather a deposition of proteinaceous mass.
The phenotypes of genetically transmitted amyloid diseases are often inherited in an autosomal dominant fashion; (Huntington's disease is in fact in most genetics texts the canonical autosomal dominant disease). Sometimes, the difference between aggressive amyloid diseases and senescent amyloid diseases is due to a mutation which makes the protein more prone to aggregation. Most commonly seen are point mutations which affect the cohesiveness of the protein and promote misfolding; other mutations cause aggregation-prone pieces of the protein to be cleaved off from the rest of the protein.
Diseases featuring amyloid
It should be noted that in almost all of the organ-specific pathologies, there is significant debate as to whether the amyloid plaques are the causal agent of the disease or if they are instead a symptom downstream of a common ideopathic agent. The associated proteins are indicated in parentheses.
- Systemic amyloidosis
- Primary amyloidosis
- Mutations in lysozyme, transthyretin, apolipoprotein B, fibrinogen
- Secondary amyloidosis
- AA amyloidosis (amyloid A protein, an acute phase protein due to chronic inflammation)
- AL amyloidosis (immunoglobulin light chains)
- Gelsolin amyloidosis (plasma gelsolin fragments).
- Primary amyloidosis
- Organ-specific amyloidosis
- Diabetes mellitus type 2 (amylin, also known as IAPP)
- Neurology
- Alzheimer's disease (a 1-40)
- Parkinson's disease (alpha-synuclein)
- Huntington's disease (huntingtin)
- Spongiform encephalopathies
- Creutzfeldt-Jakob disease (PrP in cerebrum)
- Kuru (diffuse PrP deposits in brain)
- Fatal Familial Insomnia (PrP in thalamus)
- Bovine spongiform encephalopathy (PrP in cerebrum)
1-40)Non-disease amyloids
- Native amyloids in organisms
- Yeast Prion
- Curli E. coli Protein
- Malarial coat protein
- Spider silk
Amyloid biophysics
The amyloid fold is characterized by a cross-beta sheet quaternary structure, that is, a monomeric unit contributes a beta strand to a beta sheet which spans across more than one molecule. 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 is amyloid is by placing a sample in an X-ray diffraction beam; there are two characteristic scattering bands produced at 4 and 10 angstroms (0.4 nm and 1.0 nm}, corresponding to the interstrand distances in the beta sheet structure.
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. Cross-polymerization is a phenomenon observed in vitro, and this is a putative mechanism explaining a link between diabetes and Alzheimer's disease. This is also the mechanism of prion propagation.
Histological staining
Amyloid is typically identified by a change in the fluorescence intensity of planar aromatic dyes such as Thioflavin T or Congo Red. This is generally attributed to the environmental change as these dyes intercolate 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 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.