Dispersed in the brains of Alzheimer's patients are disk-shaped lesions, about 100 µm across. Whether those lesions, or plaques, are a cause or a consequence of Alzheimer's disease is controversial, but their composition is clear. The plaques are made from fibrous aggregates—amyloid—of protein or their shorter cousins, peptides. Once sequestered in amyloid, a protein or a peptide can no longer perform its function. Even if amyloid does not directly cause Alzheimer's and other diseases, it seems at best a useless, dead-end repository of proteinaceous material. But as a new paper exemplifies, a less malign view of amyloid is emerging. Roland Riek of ETH Zürich and his collaborators have demonstrated that our bodies exploit amyloid as a temporary storage medium for a wide range of peptide hormones. Riek suspected a hormone–amyloid connection when he found that a stress hormone formed amyloid fibrils. He and his collaborators then subjected 41 other peptide hormones to a battery of biochemical, biophysical, and crystallographic tests. The finding: 75% of the peptide hormones form amyloid; and, as befits a storage medium, the amyloid can also disaggregate to release the peptides. In a final test, the team stained slices of mouse brain with hormone-sensitive and amyloid-sensitive dyes. The stained regions coincided. Riek's discovery adds to the modest but growing list of examples of so-called functional amyloid that perform useful tasks in living organisms. Evidently, amyloid is not always pernicious. (S. K. Maji et al., Science 325, 328, 2009.)—Charles Day
Hormones stored in structures usually thought toxic
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