文摘
Amyloid fibrils are large aggregates of misfolded proteins, which are often associated with various neurodegenerative diseases such as Alzheimer鈥檚, Parkinson鈥檚, Huntington鈥檚, and vascular dementia. The amount of hydrogen sulfide (H<sub>2sub>S) is known to be significantly reduced in the brain tissue of people diagnosed with Alzheimer鈥檚 disease relative to that of healthy individuals. These findings prompted us to investigate the effects of H<sub>2sub>S on the formation of amyloids in vitro using a model fibrillogenic protein hen egg white lysozyme (HEWL). HEWL forms typical 尾-sheet rich fibrils during the course of 70 min at low pH and high temperatures. The addition of H<sub>2sub>S completely inhibits the formation of 尾-sheet and amyloid fibrils, as revealed by deep UV resonance Raman (DUVRR) spectroscopy and ThT fluorescence. Nonresonance Raman spectroscopy shows that disulfide bonds undergo significant rearrangements in the presence of H<sub>2sub>S. Raman bands corresponding to disulfide (RSSR) vibrational modes in the 550鈥?00 cm<sup>鈥?sup> spectral range decrease in intensity and are accompanied by the appearance of a new 490 cm<sup>鈥?sup> band assigned to the trisulfide group (RSSSR) based on the comparison with model compounds. The formation of RSSSR was proven further using a reaction with TCEP reduction agent and LC-MS analysis of the products. Intrinsic tryptophan fluorescence study shows a strong denaturation of HEWL containing trisulfide bonds. The presented evidence indicates that H<sub>2sub>S causes the formation of trisulfide bridges, which destabilizes HEWL structure, preventing protein fibrillation. As a result, small spherical aggregates of unordered protein form, which exhibit no cytotoxicity by contrast with HEWL fibrils.