Application of Raman Spectroscopy in Amyloid Research

<div>Raman scattering spectroscopy was discovered in 1928 by CV Raman and</div><div>KS Krishnan. The technique has developed enormously and it is becoming useful in</div><div>many ways for studying biochemical events and structural intricacy of biological</div><div>macromolecules such as RNA, DNA, protein and their assemblies. The focus of this</div><div>review is on the recent application of Raman spectroscopy to research achievements of</div><div>protein aggregation and fibrillation of several proteins and peptides. Particularly we</div><div>analyzed the protein secondary structure of different assembly structures captured in</div><div>the fibril formation pathway with a particular focus on oligomeric intermediate which</div><div>is believed now to be most cytotoxic. This intermediate structure attains characteristic</div><div>morphological features while the constituent protein may/may not differ much in their</div><div>secondary and tertiary structure in the native physiological conditions. Conformation</div><div>states of proteins in the oligomeric state obtained by Raman spectroscopic analysis,</div><div>particularly aid in comprehending the structure of the oligomer and overall mechanisms</div><div>of fibrillation and amyloid formation. It has been established that the backbone amide</div><div>band and side-chain vibrations of amino acid residues present in protein molecules</div><div>largely affected the fibril formation pathway and it follows a concerted reaction</div><div>pathway, i.e. the protein molecule transform into β- sheet rich amyloid fibril via</div><div>formation of an oligomeric intermediate. However, the intriguing and interesting fact is</div><div>that the proteins maintain/attain some helical pattern in the oligomeric step. Raman</div><div>analyses established the distribution of residues in both helical and β-domain, possesses</div><div>similarity with molten globule like structure. However, in the fibrillar state, the protein</div><div>backbone attains anti-parallel β-sheet structure and several side-chain residues may be</div><div>exposed on the surface of the protein and it is evidenced in the Raman spectra of the</div><div>fibrils. The review particularly focuses on the aggregation and amyloid-like fibril</div><div>formation of hen egg-white lysozyme (HEWL) and discusses different aspects of fibril</div><div>formation mechanisms based on Raman spectroscopic data analysis.</div>