Read more about this disease, some with Classification – Types – Signs and symptoms – Genetics – Pathophysiology – Diagnosis – Screening – Prevention – Treatment and management – Cures and much more, some including pictures and video when available.
Amyloids are insoluble fibrous protein aggregates sharing specific structural traits. Abnormal accumulation of amyloid in organs may lead to amyloidosis, and may play a role in various other neurodegenerative diseases.
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]
The remainder of this article will use the biophysical context.
Amyloid is characterized by a cross-beta sheet quaternary structure; that is, the beta-strands of the stacked beta-sheets come from different protein 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 Ångstroms (0.47 nm and 1.0 nm), corresponding to the interstrand and stacking distances in beta sheets.[citation needed] 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.
Amyloid polymerization (aggregation or non-covalent 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 amylin, an amyloidogenic peptide associated with type II diabetes, but in rats and mice prolines are substituted in critical locations and amyloidogenesis does not occur.[citation needed]
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.[citation needed] 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.[citation needed]
[tubepress mode=’tag’, tagValue=’Amyloid’]