Functional amyloids signal their arrival.

Amyloids have traditionally been associated with misfolded protein aggregates and debilitating neurodegenerative diseases. However, a growing number of functional amyloids have now been described that demonstrate that amyloid formation can be an integral part of normal cellular physiology. Functional amyloid production is highly regulated, and the resulting fibers serve a variety of roles for the cells that produce them. A new role for amyloid as storage reservoirs for peptide hormones within mammalian secretory granules has been discovered. More than 30 different peptide hormones have been found to form amyloids in vitro, and both rats and mice have been shown to store hormone amyloid deposits in secretory granules. Thus, the emerging evidence adds to the diverse roles of amyloid and raises intriguing questions for both the peptide hormone and the functional amyloid fields.