Amyloid

Amyloids are aggregates of proteins that become folded into a shape that allows many copies of that protein to stick together forming fibrils. In the human body, amyloids may cause various diseases, as previously healthy proteins lose their normal physiological functions and form fibrous deposits in plaques around cells that disrupt the healthy function of tissues and organs. Such amyloids have been associated with more than 20 human diseases, known as amyloidosis, and may play a role in some neurodegenerative disorders. Some amyloid proteins are infectious; these are called prions in which the infectious form can act as a template to convert other non-infectious proteins into infectious form. Amyloids however may also have normal biological functions; for example, in the formation of fimbriae in some genera of bacteria, transmission of epigenetic traits in fungi, as well as pigment deposition and hormone release in humans.

Amyloids have been known to arise from many different proteins and polypeptides. These polypeptide chains generally form β-sheet structures that aggregate into long fibers; however, identical polypeptides can fold into multiple distinct amyloid conformations. The diversity of the conformations may have led to different forms of the prion diseases.

The name amyloid comes from the early mistaken identification by Rudolf Virchow of the substance as starch (amylum in Latin, from Greek ἄμυλον amylon), based on crude iodine-staining techniques. For a period, the scientific community debated whether or not amyloid deposits are fatty deposits or carbohydrate deposits until it was finally found (in 1859) that they are, in fact, deposits of albumoid proteinaceous material.

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