Hormone amyloids in sickness and in health

Amyloids are highly ordered cross-β-sheet containing protein aggregates associated with several dozens diseases including Alzheimer's, Creutzfeldt-Jakob and Parkinson's disease, and are also associated with functional states such as hormone storage in secretory granules. In the protein fold universe unique cross-β-sheet entity composed of an intermolecular motif repetitive in nature is key for the multiple properties of amyloids. The repeating motifs can translate a rather nonspecific interaction into a specific one through cooperativity and/or avidity, while the cross-β-sheet entity can grow by recruitment of the corresponding amyloid peptide/proteins. Because of these properties, activities of amyloids including peptide storage, template assistant, loss of function, gain of function, generation of toxicity, membrane binding, infectivity, and so on are manifold. In this review, we will discuss the possible role of the amyloid entity in the storage of hormones in secretory granules of endocrine cells as well as the disease association of hormone amyloids with particular focus on diabetes insipidus. Thus, the structure–activity relationship of hormone amyloids in health and disease will be described.