Issue 4, 2017

Detection of Zn2+ release in nitric oxide treated cells and proteome: dependence on fluorescent sensor and proteomic sulfhydryl groups

Abstract

Nitric oxide (NO) is both an important regulatory molecule in biological systems and a toxic xenobiotic. Its oxidation products react with sulfhydryl groups and either nitrosylate or oxidize them. The aerobic reaction of NO supplied by diethylamine NONOate (DEA-NO) with pig kidney LLC-PK1 cells and Zn-proteins within the isolated proteome was examined with three fluorescent zinc sensors, zinquin (ZQ), TSQ, and FluoZin-3 (FZ-3). Observations of Zn2+ labilization from Zn-proteins depended on the specific sensor used. Upon cellular exposure to DEA-NO, ZQ sequestered about 13% of the proteomic Zn2+ as Zn(ZQ)2 and additional Zn2+ as proteome·Zn–ZQ ternary complexes. TSQ, a sensor structurally related to ZQ with lower affinity for Zn2+, did not form Zn(TSQ)2. Instead, Zn2+ mobilized by DEA-NO was exclusively bound as proteome·Zn–TSQ adducts. Analogous reactions of proteome with ZQ or TSQ in vitro displayed qualitatively similar products. Titration of native proteome with Zn2+ in the presence of ZQ resulted in the sole formation of proteome·Zn–ZQ species. This result suggested that sulfhydryl groups are involved in non-specific proteomic binding of mobile Zn2+ and that the appearance of Zn(ZQ)2 after exposure of cells and proteome to DEA-NO resulted from a reduction in proteomic sulfhydryl ligands, favoring the formation of Zn(ZQ)2 instead of proteome·Zn–ZQ. With the third sensor, FluoZin-3, neither Zn–FZ-3 nor proteome·Zn–FZ-3 was detected during the reaction of proteome with DEA-NO. Instead, it reacted independently with DEA-NO with a modest enhancement of fluorescence.

Graphical abstract: Detection of Zn2+ release in nitric oxide treated cells and proteome: dependence on fluorescent sensor and proteomic sulfhydryl groups

Article information

Article type
Paper
Submitted
30 sep 2016
Accepted
29 nov 2016
First published
29 nov 2016
This article is Open Access
Creative Commons BY license

Metallomics, 2017,9, 391-401

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