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