Ni^II‐ATCUN‐Catalyzed Tyrosine Nitration in the Presence of Nitrite and Sulfite

Abstract

The nitration of tyrosine residues in proteins represents a specific footprint of the formation of reactive nitrogen species (RNS) in vivo. Here, the fusion product of orange protein (ATCUN‐ORP) was used as an in vitro model system containing an amino terminal Cu(II)‐ and Ni(II)‐binding motif (ATCUN) tag at the N‐terminus and a native tyrosine residue in the metal‐cofactor‐binding region for the formation of 3‐NO2‐Tyr (3‐NT). It is shown that NiII‐ATCUN unusually performs nitration of tyrosine at physiological pH in the presence of the NO2−/SO32−/O2 system, which is revealed by a characteristic absorbance band at 430 nm in basic medium and 350 nm in acidic medium (fingerprint of 3‐NT). Kinetics studies showed that the formation of 3‐NT depends on sulfite concentration over nitrite concentration suggesting key intermediate products, identified as oxysulfur radicals, which are detected by spin‐trap EPR study by using 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO). This study describes a new route in the formation of 3‐NT, which is proposed to be linked with the sulfur metabolism pathway associated with the progression of disease occurrence in vivo.

Copper: An Intracellular Achilles’ Heel Allowing the Targeting of Epigenetics, Kinase Pathways, and Cell Metabolism in Cancer Therapeutics

“…Tetrathiomolybdate (TM) is an inorganic tetrahedral molybdenum‐sulfur anion available as ammonium or choline salt able to sequestrate copper into a stable non‐catalytic cluster, Mo/S/Cu, through a mechanism known as Mo−Cu antagonism [67] . Among the different copper chelators, the importance of TM arises from its ability to not only inhibit the copper transfer to target sites, but, more importantly, to prevent ROS formation because of the high redox stability of Cu/TM cluster [18b] …”

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

“…The above reaction accounts for most of the formation of the nitrating agent • NO 2 in the presence of irradiated nitrite [ 27 , 37 ]. Interestingly, the occurrence of • NO and • NO 2 in the same system triggers an efficient process of nitrite regeneration: • NO + • NO 2 ⇆ N 2 O 3 [ k = 1.1 × 10 9 L mol −1 s −1 ] N 2 O 3 + H 2 O → 2 NO 2 − + 2 H + [ k = 5.3 × 10 2 s −1 ] …”

Cross‐talk Between (Hydrogen)Sulfite and Metalloproteins: Impact on Human Health

“…Indeed, human serum albumin (HSA), a most abundant plasma protein, has a close biological relationship with (bi)sulfite, enabling the sulfite‐induced HSA radicals formation, resulting in the progression of various diseases states via sulfur metabolism pathway [198] . Interestingly, albumin‐containing metal binding ATCUN motif (amino terminal Cu and Ni binding motif) [199] has no report to the formation of sulfite radical from sulfite, but designed metal‐ATCUN has ability to generate sulfite radical at physiological condition in vitro [200] . Therefore, mechanism of synergistic effect of HSA and bi(sulfite), in vivo, still is obscure.…”

“…[198] Interestingly, albumin-containing metal binding ATCUN motif (amino terminal Cu and Ni binding motif) [199] has no report to the formation of sulfite radical from sulfite, but designed metal-ATCUN has ability to generate sulfite radical at physiological condition in vitro. [200] Therefore, mechanism of synergistic effect of HSA and bi(sulfite), in vivo, still is obscure.…”