Manganese Ion-Induced Amyloid Fibrillation Kinetics of Hen Egg White-Lysozyme in Thermal and Acidic Conditions.

As manganese ions (Mn) are identified as an environmental risk factor for neurodegenerative diseases, uncovering their action mechanism on protein amyloid fibril formation is crucial for related disease treatments. Herein, we performed a combined study of Raman spectroscopy, atomic force microscopy (AFM), thioflavin T (ThT) fluorescence, and UV-vis absorption spectroscopy assays, in which the distinctive effect of Mn on the amyloid fibrillation kinetics of hen egg white-lysozyme (HEWL) was clarified at the molecular level. With thermal and acid treatments, the unfolding of protein tertiary structures is efficiently accelerated by Mn to form oligomers, as indicated by two Raman markers for the Trp residues on protein side chains: the FWHM at 759 cm and the / ratio. Meanwhile, the inconsistent evolutionary kinetics of the two indicators, as well as AFM images and UV-vis absorption spectroscopy assays, validate the tendency of Mn toward the formation of amorphous aggregates instead of amyloid fibrils. Moreover, Mn plays an accelerator role in the secondary structure transition from α-helix to organized β-sheet structures, as indicated by the N-C-C intensity at 933 cm and the amide I position of Raman spectroscopy and ThT fluorescence assays. Notably, the more significant promotion effect of Mn on the formation of amorphous aggregates provides credible clues to understand the fact that excess exposure to manganese is associated with neurological diseases