New insights into side effect of solvents on the aggregation of human islet amyloid polypeptide 11–20

Abstract

The formation of highly ordered fibrils for the human islet amyloid polypeptide (hIAPP) is considered as one of the precipitating factors of type 2 diabetes mellitus. In this study, an emerging new approach microscale thermophoresis and conventional ThT fluorescence assay were utilized to investigate the aggregation behavior of hIAPP11–20, giving a new insight of the solvent effect on the aggregation of hIAPP11–20. hIAPP11–20 displayed different aggregation behaviors in various buffers, revealing that hIAPP11–20 not only self-aggregates but also binds to solvent components. hIAPP11–20 had a higher binding affinity for Tris than other selected buffers because multiple hydrogen bonds form, resulting in weaker self-aggregation of hIAPP11–20 at the early stage of aggregation and prolonging the fibril formation process. hIAPP11–20 displayed similar self-aggregation in both HEPES and pure water. Negatively charged phosphate ions in the PBS solution ‘neutralize’ the charges carried by hIAPP11–20 itself to some extent, causing rapid aggregation of hIAPP11–20, and leading to a shorter fibrillation process of hIAPP11–20. These results revealed that solvents contribute to the aggregation of hIAPP11–20 and demonstrated the affect of solvents on the activity of biomolecules. Additionally, as a new technique, microscale thermophoresis offers a powerful and promising approach to study the early stages of aggregation of peptides or proteins.