Engineered Protein Nanopore for Real-time Monitoring Single-molecule Reaction between Cadmium Ion and Glutathione / 分析化学

ABSTRACT

The chelating reaction between glutathione peptides and divalent cadmium ion was used as a typical model for investigating the coordination chemistry of SH-containing peptides and heavy metal ions, which was essential to understand the mechanism of intracellular cadmium detoxification.Here, the mutant (CM113R)7 αHL protein nanopore equipped with a first synthesized per-6-quaternary ammonium-β-cyclodextrin (p-QABCD) was used as nanoreactor and detector to investigate the single-molecule reaction of GSH molecules and Cd2+ ions.Different reaction pathways, intermediates, and products could be recognized.Cd2+-GSH reaction was highly dependent on the solution pH.The Cd(GSH)2 was formed at pH 7.4, while the Cd(GSH)2 and Cd2(GSH)2 were formed at pH 9.0.Cd2(GSH)2 was formed by two possible pathways (1) A Cd2+ ion primarily coordinated with the thiol group of two GSH molecules to form Cd(GSH)2, and then the second Cd2+ ion quickly incorporated with the deprotonated amino group of Cd(GSH)2 to form Cd2(GSH)2;(2) Two Cd2+ ions separately coordinated with the thiol and deprotonated amino group of one GSH molecule to form Cd2(GSH)1, and the second GSH molecule quickly bounded to Cd2+ ions to form Cd2(GSH)2.This work studied the chelating reaction between metal ions and bioactive glutathione at single-molecule level without labeling and chemical modification, and would be important to further understand intracellular mechanisms of detoxification of heavy metals and greatly expand the research field of nanopore single-molecule technique.