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Systematic characterization of the covalent interactions between (−)‐epigallocatechin gallate and peptides under physiological conditions by mass spectrometry
Author(s) -
Cao Dong,
Zhang Yangjun,
Zhang Huihui,
Zhong Liangwei,
Qian Xiaohong
Publication year - 2009
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.3985
Subject(s) - chemistry , mass spectrometry , gallate , characterization (materials science) , covalent bond , protein mass spectrometry , chromatography , epigallocatechin gallate , combinatorial chemistry , tandem mass spectrometry , nanotechnology , organic chemistry , polyphenol , nuclear chemistry , antioxidant , materials science
(−)‐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°C). In this work, the covalent interactions between EGCG and model peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and α ‐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°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 α ‐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 > α‐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 . Copyright © 2009 John Wiley & Sons, Ltd.