Structural Biology of Calcitonin: From Aqueous Therapeutic Properties to Amyloid Aggregation

Abstract

AbstractUnder appropriate conditions, peptides and proteins can assemble from their native state into prefibrillar oligomers and then mature into fibrillar aggregates. This transition forms the molecular basis of several pathologies, often related to the deposition of these amyloid fibrils. Several hormone peptides involved in fundamental biological processes have the tendency to self‐assemble into amyloid fibrils, resulting in a loss of their native functions, and more importantly, entailing devastating consequences, such as the formation of amyloid depositions. Calcitonin is a 32 amino‐acid hormone peptide that can be considered a molecular paradigm for the central events associated with hormone misfolding. Calcitonin in its native form is involved in various physiological functions, including mediating calcium homeostasis and maintaining bone structure. It is the latter function that has motivated the use of calcitonin as an aqueous therapeutic agent for the treatment of bone‐related pathologies such as osteoporosis and Paget's disease. Despite some success as a therapeutic, calcitonin's ability to control these diseases is limited by its aggregation along the canonical amyloid aggregation pathway, compromising its long‐term stability as a therapeutic agent. A better understanding of the misfolding process would not only provide the structural basis to improve calcitonin's long‐term stability and activity as a therapeutic, but also provide valuable insights into pathological aggregation of other amyloids. In this work, we review the physiological roles of calcitonin, its structure, and aggregation process, and consider the effects of calcitonin's structure on its role as a therapeutic.