The Impact Of Morin On HEWL Amyloid Fibril Formation

Fibrillar amyloid formed by the aggregation of misfolded proteins, deposits in tissue or organ. Currently, at least 30 different fibril proteins are known to be involved in human amyloid diseases. A number of chronic degenerative diseases, including Parkinson’s disease, Alzheimer’s disease, type-2 diabetes and some of the coronary heart diseases are associated with amyloid fibrils. Interestingly, a generic property has been found in all fibrillogenic polypeptides irrespective of their protein sequences or tertiary structure. Thus, as a result of the similar structure, toxicity and tinctorial properties found across different forms of amyloid fibrils, the concept of developing a therapeutic agent against amyloidosis has attracted more interest among investigators working in this field.Currently, almost no therapies had been developed for human diseases associated with amyloid formation. Consequently, the search for new compounds interfering with aggregation of amyloid proteins is thought to be a rewarding strategy to develop new therapies. Natural polyphenolic compounds are found extensively in foods and herbal remedies and considered as promising pharmaceuticals against amyloid diseases.Hen egg white lysozyme (HEWL) is a structural homologue of human lysozyme, whose amyloidogenic variants correlate with the incidence of systemic amyloidosis. HEWL is also one of the best characterized and most studied proteins. Its folding-unfolding process has been studied in detail and unfolding intermediates have been identified. In this study we showed that Morin could significantly inhibit the fibrillation of HEWL, a generic amyloid-forming model protein. Spectrofluorometric and computational studies showed that Morin inhibited the amyloid fibril formation of HEWL by entering the cleft of HEWL to bind to the aggregation prone region of the β-domain of HEWL, thereby stabilizing the molecule in its native-like state as opposed to redirecting aggregation toward amorphous aggregates. TEM observations confirmed the inhibitory effect of Morin on fibril formation by HEWL and showed that it attenuated the capacity of HEWL fibrillation in a dose-dependent manner. Interestingly, along with increases in Morin concentration, the observed amorphous aggregates consisting of Morin and HEWL became bigger, and MTT assay confirmed that Morin could decrease the cytotoxicity of HEWL fibril. We proposed that after entering the cleft, the excess Morin would stick to the protein surface, thereby reducing the interaction between the protein and water molecules. The mechanism by which Morin inhibited HEWL fibrillation not only allows us to better understand the molecular action of a molecule, but this information can also be applied to the designing of new inhibitors specific for targeting fibril-forming polypeptide.