title: (-)-epigallocatechin-3-gallate (EGCG) maintains kappa-casein in its pre-fibrillar state without redirecting its aggregation pathway.
abstract: The polyphenol (-)-epigallocatechin-3-gallate (EGCG) has recently attracted much research interest in the field of protein-misfolding diseases because of its potent anti-amyloid activity against amyloid-beta, alpha-synuclein and huntingtin, the amyloid-fibril-forming proteins involved in Alzheimer's, Parkinson's and Huntington's diseases, respectively. EGCG redirects the aggregation of these polypeptides to a disordered off-folding pathway that results in the formation of non-toxic amorphous aggregates. Whether this anti-fibril activity is specific to these disease-related target proteins or is more generic remains to be established. In addition, the mechanism by which EGCG exerts its effects, as with all anti-amyloidogenic polyphenols, remains unclear. To address these aspects, we have investigated the ability of EGCG to inhibit amyloidogenesis of the generic model fibril-forming protein RCMkappa-CN (reduced and carboxymethylated kappa-casein) and thereby protect pheochromocytoma-12 cells from RCMkappa-CN amyloid-induced toxicity. We found that EGCG potently inhibits in vitro fibril formation by RCMkappa-CN [the IC(50) for 50 microM RCMkappa-CN is 13+/-1 microM]. Biophysical studies reveal that EGCG prevents RCMkappa-CN fibril formation by stabilising RCMkappa-CN in its native-like state rather than by redirecting its aggregation to the disordered, amorphous aggregation pathway. Thus, while it appears that EGCG is a generic inhibitor of amyloid-fibril formation, the mechanism by which it achieves this inhibition is specific to the target fibril-forming polypeptide. It is proposed that EGCG is directed to the amyloidogenic sheet-turn-sheet motif of monomeric RCMkappa-CN with high affinity by strong non-specific hydrophobic associations. Additional non-covalent pi-pi stacking interactions between the polyphenolic and aromatic residues common to the amyloidogenic sequence are also implicated.
authors.affiliation: The University of Adelaide, South Australia, Australia.
authors.forename: Sean A
authors.initials: SA
authors.lastname: Hudson
authors.forename: Heath
authors.initials: H
authors.lastname: Ecroyd
authors.forename: Francis C
authors.initials: FC
authors.lastname: Dehle
authors.forename: Ian F
authors.initials: IF
authors.lastname: Musgrave
authors.forename: John A
authors.initials: JA
authors.lastname: Carver
mesh_terms: D000682:Amyloid / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D002364:Caseins / Q000737:chemistry / Q000378:metabolism; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D006801:Humans; D015394:Molecular Structure; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D000682:Amyloid; D002364:Caseins; D002392:Catechin; C045651:epigallocatechin gallate