Biophysical investigations of hen Iysozyme aggregation and its inhibition at alkaline pH

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Protein aggregation has been considered as undesired product, while incorrect folding of proteins. It is associated with the many of consequences like neurodegenerative diseases (e.g. AlzheimerDs and ParkinsonDs) and non-neurodegenerative disease (e.g. Type II diabetes, systemic amylodosis), recovery of over expressed therapeutics proteins, and formulation for the protein drug. Protein aggregation occurs through different and complex pathway, forming intermediate products like oligomers. These oligomers further participate into amyloid fibril formation. Previously it has been considered that amyloid fibrils are responsible for amyloidogenic diseases. However recent finding indicates that oligomeric products are likely have a role in causing diseases like AlzheimerDs, ParkinsonDs in late age. Apart from clinical significance of amyloid fibril, recent study impresses that amyloid fibers have a great potential to be used as biomaterials and nanodevices like nanovechicles, nano wire, nanopores and nanoscaffold. These intrinsic properties were developed because of its ordered cross D D sheet structure and self assembling property at a nanoscale. Hence, in this thesis some salient biophysical investigation was carried out on growth of hen lysozyme oligomers, amyloid fibers formation and its inhibition. It has shown that hen lysozyme forms amorphous and ordered (fibrillar) aggregates in pH 12.2 at room temperature. These aggregates later stabilized through intermolecular disulfide bond formation among aggregates. Subsequently, it was also studied that how surfactants (SDS, CTAB) and DTT affects the aggregation of lysozyme. For this investigation, the lysozyme was incubated in pH 12.2 at room temperature and aggregation was monitored at different incubation period. Size heterogeneity and morphology of hen lysozyme aggregates was monitored employing gel filtration chromatography and atomic force microscopy techniques. The size heterogeneity was observed based on the spectral profile of gel filtration elution volume. Here, it was found that at early time lysozyme spontaneously forms mixture of aggregates containing more populated small aggregates in pH 12.2 at room temperature. However as time of incubation increases nearly 120 hours the big aggregates predominate. However in presence of SDS, HEWL forms large molecular mass or unusual shape. In presence of CTAB lysozyme aggregate was found relatively smaller and compact compare to SDS. Although in presence of DTT lysozyme conformation was remain compact and its size/shape was comparatively similar to monomer..
Supervisor: R Swaminathon