Concentration-Dependent Effect of Nickel Ions on Amyloid Fibril Formation Kinetics of Hen Egg White Lysozyme: a Raman Spectroscopy Study

Nickel, an important transition metal element, is one of the trace elements for human body and has a crucial impact on life and health. Some evidences show the excess exposure to metal ions might be associated with neurological diseases. Herein, we applied Raman spectroscopy to study the Ni(II) ion effect on kinetics of amyloid fibrillation of hen egg white lysozyme (HEWL) in thermal and acidic conditions. Using the well-known Raman indicators for protein tertiary and secondary structures, we monitored and analyzed the concentration effect of Ni(II) ions on the unfolding of tertiary structures and the transformation of secondary structures. The experimental evidence validates the accelerator role of the metal ion in the kinetics. Notably, the additional analysis of the amide I band profile, combined with thioflavin-T fluorescence assays, clearly indicates the inhibitory effect of Ni(II) ions on the formation of amyloid fibrils with organized β-sheets structures. Instead, a more significant promotion influence is affirmed on the assembly into other aggregates with disordered structures. The present results provide rich information about the specific metal-mediated protein fibrillation.