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Human insulin fibrillogenesis in the presence of epigallocatechin gallate and melatonin: Structural insights from a biophysical approach

Carbonaro, M., Ripanti, F., Filabozzi, A., Minicozzi, V., Stellato, F., Placidi, E., Morante, S., Di Venere, A., Nicolai, E., Postorino, P., Nucara, A.
International journal of biological macromolecules 2018 v.115 pp. 1157-1164
Raman spectroscopy, atomic force microscopy, epigallocatechin gallate, fluorescence, humans, hydrophobicity, infrared spectroscopy, insulin, light scattering, melatonin
Fibrillogenesis of monomeric human insulin in the presence or absence of (-)-epigallocatechin-3-gallate and melatonin was here investigated using a multi-technique approach. Results from Raman and Infrared spectroscopy pointed out that a high content of intermolecular β-sheet aggregates is formed after long-term incubation. However, near UV experiments, Dynamic Light Scattering, Thioflavin-T fluorescence measurements and Atomic Force Microscopy revealed that the kinetics from native-to-fibrillar state of insulin is hampered only in the presence of (-)-epigallocatechin-3-gallate. Molecular dynamic simulations indicated that this compound binds near the B11–B18 protein segment, where hydrophobic residues responsible for the beginning of cooperative aggregation are located. Such a preferential binding region is not recognized by melatonin, a highly mobile molecule, which indeed does not affect fibril formation. The results of the present study demonstrate that (-)-epigallocatechin-3-gallate interferes with the insulin nucleation phase, giving rise to amorphous aggregates in the early stages of the aggregation process.