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–Cα–C stretching band at ∼930 cm–1 clearly indicated the presence of a substantial amount of α-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 α-helical folds, which is found in the case of monomeric samples. Circular dichroism study also revealed the presence of typical α-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 β-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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Reactive oxygen species e.g. O(2)(*-), H(2)O(2) and *OH generated by the induction of oxidative stress exert a potential threat on the activity of endogenous antioxidant enzymes and substantially influence the aging process and age-dependant neuropathology. Chemical antioxidant is almost ineffective in protecting neuronal cells from oxidative damage as Blood Brain Barrier exists in between blood and brain interstitial fluid that restricts undegradable influx from the circulation into cerebral region. Quercetin (QC), a flavonoidal antioxidant is known as a potent antioxidant for its polyphenolic configuration. Formulation of QC in polylactide nanocapsule has been done and the efficacy of this vesicular flavonoid has been tested against cerebral ischemia induced oxidative damage in young and old rat brains. Antioxidant potential of QC loaded in nanocapsule (QC 7.2 mmol/kg b.wt., size 50 nm) was investigated by an in vivo model of cerebral ischemia and reperfusion on Sprague Dawley young (2 months, b.wt. 160-180 g) and aged (20 months, b.wt. 415-440 g) rats. Diene level, the index of lipid peroxidation and GSSG/GSH ratio were found to be higher in normal aged, compared to normal young rat brain. Endogenous antioxidants activities were lower in aged rat brain compared to young. Further reduction of these antioxidants were observed in aged rat brain by the induction of cerebral ischemia - reperfusion. Nanocapsule encapsulated QC treatment resulted a significant protection to endogenous antioxidant enzymes against ischemia induced oxidative damage in neuronal cells of young and old rats.

An amyloidogenic region (AR) in a protein sequence plays a significant role in protein aggregation and amyloid formation. We have investigated the sequence complexity of AR that is present in intrinsically disordered human proteins. More than 80% human proteins in the disordered protein databases (DisProt+IDEAL) contained one or more ARs. With decrease of protein disorder, AR content in the protein sequence was decreased. A probability density distribution analysis and discrete analysis of AR sequences showed that ∼8% residue in a protein sequence was in AR and the region was in average 8 residues long. The residues in the AR were high in sequence complexity and it seldom overlapped with low complexity regions (LCR), which was largely abundant in disorder proteins. The sequences in the AR showed mixed conformational adaptability towards α-helix, β-sheet/strand and coil conformations.