title: Systematic characterization of the covalent interactions between (-)-epigallocatechin gallate and peptides under physiological conditions by mass spectrometry.
abstract: (-)-Epigallocatechin gallate (EGCG) is a major bioactive component in leaves of green tea, and has been widely investigated for its anti-tumor activity. The interaction between EGCG and the key peptides or proteins (e.g. glutathione, enzymes) in vivo is thought to be involved in the toxicity and anti-cancer mechanism of EGCG. However, the true anti-tumor mechanism of EGCG is not clear, and few studies have focused on the reactivity of EGCG toward peptides or proteins under physiological conditions (pH 7.4, 37 degrees C). In this work, the covalent interactions between EGCG and model peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and alpha-NH(2) of the N-terminus of peptides) under physiological condition were fully characterized using mass spectrometry. It was found that EGCG can react with the thiol groups of peptides to form adducts under physiological conditions (pH 7.4, 37 degrees C), even in the absence of the peroxidase/hydrogen peroxide system. Besides the thiol groups of peptides, it is firstly reported that EGCG also reacts with alpha-NH(2) of the N-terminus or arginine residues of model peptides to form Schiff base adducts, and the methionine residues of model peptides can be easily oxidized by hydrogen peroxide (H(2)O(2)) generated during the process of EGCG auto-oxidation to form methionine sulfoxide products. The preference for the reaction of nucleophlic residues of peptides with EGCG was determined to have the following order: Cys > alpha-NH(2) of the N-terminus > Arg. The neutral loss ions of [M+H-170](+) and [M+H-138](+) were detected in all tandem mass spectra of the EGCG adducts of peptides, which indicates that these two neutral loss ions can be considered as the characteristic neutral loss ions of peptides modified by EGCG. Results of the present research provide insights into the toxicology and anti-tumor mechanism of EGCG in vivo.
authors.affiliation: State Key Laboratory of Proteomics, Beijing Proteome Research Center, Beijing Institute of Radiation Medicine, 33 Life Science Park Road, Changping District, Beijing 102206, China.
authors.forename: Dong
authors.initials: D
authors.lastname: Cao
authors.forename: Yangjun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Huihui
authors.initials: H
authors.lastname: Zhang
authors.forename: Liangwei
authors.initials: L
authors.lastname: Zhong
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Qian
mesh_terms: D001120:Arginine / Q000737:chemistry; D002392:Catechin / Q000031:analogs & derivatives* / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry / Q000379:methods*; D008715:Methionine / Q000737:chemistry; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000737:chemistry; D053719:Tandem Mass Spectrometry / Q000379:methods; D013696:Temperature
chemical_list: D010455:Peptides; D013438:Sulfhydryl Compounds; D002392:Catechin; D001120:Arginine; D008715:Methionine; C045651:epigallocatechin gallate; D003545:Cysteine