Modulation of amylin and calcitonin receptor activation by hybrid peptides.

Calcitonin peptide hormone controls calcium homeostasis by activating the calcitonin receptor. When the calcitonin receptor forms a complex with an accessory protein, the complex functions as the receptors for another peptide hormone amylin. The amylin receptors are the drug target for diabetes and obesity treatment. Since human amylin can produce aggregates, rat amylin that does not form aggregates has been commonly used for research. Interestingly, calcitonin originated from salmons was reported to interact with human amylin receptors with higher affinity/potency than endogenous rat amylin. Here, the peptide hybrid was made of a rat amylin N-terminal fragment and a salmon calcitonin C-terminal fragment. This novel hybrid peptide showed higher potency for human amylin receptor 1/2 activation by 6- to 8-fold than endogenous rat amylin. To further examine the role of the peptide C-terminal fragment in receptor activation, another hybrid peptide was made where salmon calcitonin N-terminal 21 amino acids were fused with rat amylin C-terminal 11 amino acids. The rat amylin C-terminal fragment was previously reported to have relatively low affinity for calcitonin receptor extracellular domain. As expected, this calcitonin-amylin hybrid peptide decreased the potency for calcitonin receptor activation by 3-fold compared to salmon calcitonin. The hybrid strategy used in this study significantly changed the peptide potency for amylin and calcitonin receptor activation. These results provide insight into the role of peptide C-terminal fragments in modulating amylin and calcitonin receptor activation.