The fibrous protein aggregates, so-called β-amyloids, are implicated in a variety of neurodegenerative disorders such as Alzheimer’s, Parkinson’s, Huntington’s disease or cerebral β-amyloid angiopathy. Study of protein folding and misfolding is therefore crucial for further diagnostics and treatment of these diseases. Traditional techniques for protein structure determination such as X-ray or NMR are often not suitable to quickly track changes in 3D protein structures in solutions. Moreover, limited solubility and molecular size of β-amyloids represent another problem.
In the presented work, chiral spectroscopic methods based on Vibrational Optical Activity (VOA), were used to study fibrous protein aggregates formed from model proteins polyglutamic acid (PGA) and hen-egg lysozyme (HEL). Infrared absorption and vibrational circular dichroism (VCD) proved to be very valuable in detection of such extended structures. The amide I band provides information on the peptide secondary structure, while enhanced VCD signal and its sign indicate a longer range arrangement. On the other hand, Raman optical activity (ROA) was not sensitive enough to study β-amyloid structures alone. Therefore EuCl3 and water soluble europium complexes were used as probes of molecular chirality in ROA measurements. It was shown that β-amyloids can interact with solvated Eu3+ ions or their complexes inducing a strong ROA signal due to chirality transfer.
Support from the Grant Agency of the Czech Republic (grant numbers 16-04902S and 15-09072S) is gratefully acknowledged.