Computational insights into the aggregation mechanism of human calcitonin

Human calcitonin (hCT) is a peptide hormone that regulates calcium homeostasis, but its abnormal aggregation can disrupt physiological functions and increase the risk of medullary thyroid carcinoma. To elucidate the mechanisms underlying hCT aggregation, we investigated the self-assembly dynamics of hCT segments (hCT_1-14, hCT_15-25, and hCT_26-32) and the folding and dimerization of full-length hCT_1-32 through microsecond atomistic discrete molecular dynamics (DMD) simulations. Our results revealed that hCT_1-14 and hCT_26-32 predominantly existed as isolated monomers with transient small-sized oligomers, indicating weak aggregation tendencies. In contrast, hCT_15-25 exhibited robust aggregation capability, forming stable β-sheet aggregates independently. Full-length hCT_1-32 monomers displayed dynamic helical structures, with dimerization decreasing helix content and enhancing β-sheet formation. The transition to β-sheets in full-length hCT_1-32 correlated with the loss of helical structure in the hCT_15-25 region. Conformations with high helical content in hCT_15-25 corresponded to significantly reduced β-sheet structures across the peptide, underscoring the importance of helical stability in preventing β-sheet conversion. Thus, the development of amyloid-resistant hCT analogues should focus on enhancing helical stability in this crucial region. Overall, our study not only elucidates the aggregation mechanism of hCT but also identifies a critical target for designing drug inhibitors to prevent hCT aggregation.