Journal
JOURNAL OF PHYSICAL CHEMISTRY B
Volume 124, Issue 1, Pages 50-60Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcb.9b09139
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Funding
- CSIR [BSC0113, BSC0115, BSC0121]
- UGC
- DBT, New Delhi [GAP -299]
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Lysozyme, like many other well-folded globular proteins, under stressful conditions produces nanoscale oligomer assembly and amyloid-like fibrillar aggregates. With engaging Raman microscopy, we made a critical structural analysis of oligomer and other assembly structures of lysozyme obtained from hen egg white and provided a quantitative estimation of a protein secondary structure in different states of its fibrillation. A strong amide I Raman band at 1660 cm(-1) and a N-C alpha-C stretching band at similar to 930 cm(-1) clearly indicated the presence of a substantial amount of alpha-helical folds of the protein in its oligomeric assembly state. In addition, analysis of the amide III region and Raman difference spectra suggested an ample presence of a PPII-like secondary structure in these oligomers without causing major loss of alpha-helical folds, which is found in the case of monomeric samples. Circular dichroism study also revealed the presence of typical alpha-helical folds in the oligomeric state. Nonetheless, most of the Raman bands associated with aromatic residues and disulfide (-S-S-) linkages broadened in the oligomeric state and indicated a collapse in the tertiary structure. In the fibrillar state of assembly, the amide I band became much sharper and enriched with the beta-sheet secondary structure. Also, the disulfide bond vibration in matured fibrils became much weaker compared to monomer and oligomers and thus confirmed certain loss/cleavage of this bond during fibrillation. The Raman band of tryptophan and tyrosine residues indicated that some of these residues experienced a greater hydrophobic microenvironment in the fibrillar state than the protein in the oligomeric state of the assembly structure.
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