Objective

Misfolding and aggregation of human prion protein (HuPrP) is linked to a variety of neurological disorders, commonly known as the Transmissible Spongiform Encephalopathies (TSEs). Despite several efforts to recognize effective small molecule inhibitors of amyloid disorders, at present no effective therapeutic agent is available for the neurodengerative amyloidosis. Green tea polyphenols inhibit the aggregation of some amyloidogenic proteins and may initiate the formation of non-toxic, off pathway unstructured oligomers. Herein, we examined the protective efficacy of two green tea polyphenols, Epicatechin gallate (ECG) and Epigallocatechin (EGC) against the amyloid conversion of cellular human prion protein to the disease forming scrapie conformation, employing a combination of computational and experimental approach. Collective results from ThT, TEM, AFM, DLS and CD experiments show that ECG and EGC both exhibit an inhibitory effect on the structural transition of HuPrP monomers and protofibrillar structures into beta sheet rich structures, thereby reducing the amyloid fibrillization of HuPrP. Further, MTT assay and confocal microscopy revealed that both the catechins increase the cell viability by reducing toxicity associated with oligomeric species in neuronal cell models. But interestingly, ECG has a stronger inhibitory effect on HuPrP amyloidogenesis as compared to EGC due to minor differences in the structure of these two polyphenols. Both the compounds stably interact with the hydrophobic residues in the binding pocket of HuPrP which encompasses the β2-α2 loop and the C-terminal region of the α3 helix. Binding mechanisms of ECG and EGC with HuPrP was analyzed by molecular dynamics simulations. The 4Å region of HuPrP binding pocket around these two compounds reveals that ECG forms more hydrogen bonds and hydrophobic interactions (as compared to EGC) with the residues critical in the conversion of cellular to scrapie form of HuPrP, this may be the reason behind making ECG a more potent inhibitor. Thus, small molecules (like catechins and polyphenols) that can directly interact with the critical hydrophobic patches of HuPrP can act as inhibitors of prion amyloidogenesis and hold a substantial therapeutic potential. The green tea polyphenols might also be of synergistic benefit in treating the prion diseases.