Two-step reaction mechanism reveals new antioxidant capability of cysteine disulfides against hydroxyl radical attack

Abstract

Cysteine disulfides, which constitute an important component in biological redox buffer systems, are highly reactive toward the hydroxyl radical (•OH). The mechanistic details of this reaction, however, remain unclear, largely due to the difficulty in characterizing unstable reaction products. Herein, we have developed a combined approach involving mass spectrometry (MS) and theoretical calculations to investigate reactions of •OH with cysteine disulfides (Cys–S–S–R) in the gas phase. Four types of first-generation products were identified: protonated ions of the cysteine thiyl radical (+Cys–S•), cysteine (+Cys–SH), cysteine sulfinyl radical (+Cys–SO•), and cysteine sulfenic acid (+Cys–SOH). The relative reaction rates and product branching ratios responded sensitively to the electronic property of the R group, providing key evidence to deriving a two-step reaction mechanism. The first step involved •OH conducting a back-side attack on one of the sulfur atoms, forming sulfenic acid (–SOH) and thiyl radical (–S•) product pairs. A subsequent H transfer step within the product complex was favored for protonated systems, generating sulfinyl radical (–SO•) and thiol (–SH) products. Because sulfenic acid is a potent scavenger of peroxyl radicals, our results implied that cysteine disulfide can form two lines of defense against reactive oxygen species, one using the cysteine disulfide itself and the other using the sulfenic acid product of the conversion of cysteine disulfide. This aspect suggested that, in a nonpolar environment, cysteine disulfides might play a more active role in the antioxidant network than previously appreciated.

Multi-omic screening of invasive GBM cells in engineered biomaterials and patient biopsies reveals targetable transsulfuration pathway alterations

“…CTH knockdown did not alter levels of superoxide in cultured GBM43 cells in normal (400 µM) and low (200 µM) cysteine concentrations as measured by the MitoSOX TM probe (P=0.8 at 400 µM cysteine; P=0.2 at 200 µM cysteine; Extended Data Fig.6d), suggesting that hydroxyl radical accumulates in cells deprived of cysteine due to CTH knockdown. These results are consistent with cell-free chemistry studies implicating cysteine disulfides in the antioxidant response to hydroxyl radical attack 22. Interestingly, levels of ROS assessed by the.…”

“…These results are consistent with cell-free chemistry studies implicating cysteine disulfides in the antioxidant response to hydroxyl radical attack. 22 Interestingly, levels of ROS assessed by the CellROX TM reagent did not differ between the core and invasive fractions of GBM43 control and CTH knockdown cells in 3D hydrogel devices ( Extended Data Figs. 6e-f ), possibly reflecting greater hypoxia in the devices.…”

Multiscale structural control of thiostannate chalcogels with two-dimensional crystalline constituents

“…At pH 2–10, NMSC-1 exhibited 37.4–56.1% (±4–26 mg g −1 standard deviation) of the original Cs + -removal capacity (Fig. 5d ), indicating a potential ion-exchange competition with H 3 O + under acidic conditions and hydroxyl group attacks on the sulfidic sites under basic conditions 66 .…”

Role of Oxidative Stress in Heart Failure: Insights from Gene Transfer Studies

“…Cysteine disulfides, which constitute an important component in biological redox buffer systems, are highly reactive toward the hydroxyl radical (HO . ) [31].…”