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

[Image: see text] As manganese ions (Mn(2+)) 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(2+) 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(2+) to form oligomers, as indicated by two Raman markers for the Trp residues on protein side chains: the FWHM at 759 cm(–1) and the I(1340)/I(1360) 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(2+) toward the formation of amorphous aggregates instead of amyloid fibrils. Moreover, Mn(2+) plays an accelerator role in the secondary structure transition from α-helix to organized β-sheet structures, as indicated by the N–C(α)-C intensity at 933 cm(–1) and the amide I position of Raman spectroscopy and ThT fluorescence assays. Notably, the more significant promotion effect of Mn(2+) on the formation of amorphous aggregates provides credible clues to understand the fact that excess exposure to manganese is associated with neurological diseases(.)