title: Green tea polyphenol epigallocatechin-3-gallate (EGCG) induced intermolecular cross-linking of membrane proteins.
abstract: Increasing evidence has demonstrated that EGCG possesses prooxidant potential in biological systems, including modifying proteins, breaking DNA strands and inducing the generation of reactive oxygen species. In the present study, the prooxidant effect of EGCG on erythrocyte membranes was investigated. SDS-PAGE and NBT-staining assay were utilized to detect the catechol-protein adducts that generated upon treating the membranes with EGCG. The results indicated that EGCG was able to bind covalently to sulfhydryl groups of membrane proteins, leading to the formation of protein aggregates with intermolecular cross-linking. We suggested that the catechol-quinone originated from the oxidation of EGCG acted as a cross-linker on which peptide chains were combined through thiol-S-alkylation at the C2- and C6-sites of the gallyl ring. EGC showed similar effects as EGCG on the ghost membranes, whereas ECG and EC did not, suggesting that a structure with a gallyl moiety is a prerequisite for a catechin to induce the aggregation of membrane proteins and to deplete membrane sulfhydryls. EDTA and ascorbic acid inhibited the EGCG-induced aggregation of membrane proteins by blocking the formation of catechol-quinone. The information of the present study may provide a fresh insight into the prooxidant effect and cytotoxicity of tea catechins.
authors.affiliation: Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, College of Chemistry and Material Science, Shaanxi Normal University, Xi'an 710062, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Chen
authors.forename: Jian-Bo
authors.initials: JB
authors.lastname: Wang
authors.forename: Xian-Qing
authors.initials: XQ
authors.lastname: Zhang
authors.forename: Jing
authors.initials: J
authors.lastname: Ren
authors.forename: Cheng-Ming
authors.initials: CM
authors.lastname: Zeng
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology; D016227:Benzoquinones / Q000737:chemistry / Q000494:pharmacology; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008970:Molecular Weight; D010636:Phenols / Q000494:pharmacology*; D059808:Polyphenols; D055503:Protein Multimerization / Q000187:drug effects; D020836:Protein Structure, Quaternary; D017382:Reactive Oxygen Species / Q000494:pharmacology; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013662:Tea / Q000737:chemistry*
chemical_list: D016227:Benzoquinones; D003432:Cross-Linking Reagents; D005419:Flavonoids; D008565:Membrane Proteins; D010636:Phenols; D059808:Polyphenols; D017382:Reactive Oxygen Species; D013438:Sulfhydryl Compounds; D013662:Tea; C004532:quinone; D002392:Catechin; D004492:Edetic Acid; C045651:epigallocatechin gallate; D001205:Ascorbic Acid