title: Docking studies and model development of tea polyphenol proteasome inhibitors: applications to rational drug design.
abstract: Previously, we demonstrated that natural and synthetic ester bond-containing green tea polyphenols were potent and specific non-peptide proteasome inhibitors. However, the molecular mechanism of inhibition is currently unknown. Here, we report that inhibition of the chymotrypsin activity of the 20S proteasome by (-)-epigallocatechin-3-gallate (EGCG) is time-dependent and irreversible, implicating acylation of the beta5-subunit's catalytic N-terminal threonine (Thr 1). This knowledge is used, along with in silico docking experiments, to aid in the understanding of binding and inhibition. On the basis of these docking experiments, we propose that (-)-EGCG binds the chymotrypsin site in an orientation and conformation that is suitable for a nucleophilic attack by Thr 1. Consistently, the distance from the electrophilic carbonyl carbon of (-)-EGCG to the hydroxyl group of Thr 1 was measured as 3.18 A. Furthermore, the A ring of (-)-EGCG acts as a tyrosine mimic, binding to the hydrophobic S1 pocket of the beta5-subunit. In the process, the (-)-EGCG scissile bond may become strained, which could lower the activation energy for attack by the hydroxyl group of Thr 1. This model is validated by comparison of predicted and actual activities of several EGCG analogs, either naturally occurring, previously synthesized, or rationally synthesized.
authors.affiliation: Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, and Department of Biochemistry and Molecular Biology, College of Medicine, University of South Florida, Tampa, Florida, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Smith
authors.forename: Kenyon G
authors.initials: KG
authors.lastname: Daniel
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Wang
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Guida
authors.forename: Tak-Hang
authors.initials: TH
authors.lastname: Chan
authors.forename: Q Ping
authors.initials: QP
authors.lastname: Dou
mesh_terms: D000577:Amides / Q000737:chemistry; D001665:Binding Sites; D028241:Camellia sinensis / Q000737:chemistry; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D002918:Chymotrypsin / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D015195:Drug Design; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D010636:Phenols / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D059808:Polyphenols; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism
chemical_list: D000577:Amides; D015853:Cysteine Proteinase Inhibitors; D005419:Flavonoids; D009097:Multienzyme Complexes; D010636:Phenols; D059808:Polyphenols; D021122:Protein Subunits; D002392:Catechin; C045651:epigallocatechin gallate; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex