TY - JOUR

T1 - Inhibition and crosslinking of the selenoprotein thioredoxin reductase-1 by p-benzoquinone

AU - Shu, Nan

AU - Cheng, Qing

AU - Arner, Elias S. J.

AU - Davies, Michael J.

PY - 2020

Y1 - 2020

N2 - Quinones are common in nature, and often cytotoxic. Their proposed toxicity mechanisms involve redox cycling with radical generation, and/or reactions with nucleophiles, such as protein cysteine (Cys) residues, forming adducts via Michael addition reactions. The selenenyl anion of selenocysteine (Sec) is a stronger nucleophile, more prevalent at physiological pH, and more reactive than the corresponding thiolate anion of Cys. We therefore hypothesized that Sec residues should be readily modified by quinones and with potential consequences for the structure and function of selenoproteins. Here, we report data on the interaction of p-benzoquinone (BQ) with the selenoprotein thioredoxin reductase-1 (TrxR1), which exposes an accessible Sec residue upon physiological reduction by NADPH. Our results reveal that BQ targets NADPH-reduced TrxR1 and inhibits its activity using 5,5'-dithiobis(2-nitrobenzoic acid) or juglone as model substrates, consistent with the targeting of both the Cys and Sec residues of TrxR1. In the absence of NADPH, BQ modified the non-catalytic Cys residues, leading to subunit crosslinking, mainly through disulfides, which also resulted in some loss of activity. This crosslinking was time-dependent and independent of the Sec residue. Addition of NADPH after BQ pre-treatment could resolve the disulfide-linked crosslinking. TrxR activity loss was also observed upon incubation of J774A.1 cells or cell lysates with BQ. These data suggest that BQ readily targets TrxR1, albeit in a rather complex manner, which results in structural changes and loss of enzyme activity. We suggest that TrxR1 targeting can explain some of the cytotoxicity of BQ, and potentially also that of other quinone compounds

AB - Quinones are common in nature, and often cytotoxic. Their proposed toxicity mechanisms involve redox cycling with radical generation, and/or reactions with nucleophiles, such as protein cysteine (Cys) residues, forming adducts via Michael addition reactions. The selenenyl anion of selenocysteine (Sec) is a stronger nucleophile, more prevalent at physiological pH, and more reactive than the corresponding thiolate anion of Cys. We therefore hypothesized that Sec residues should be readily modified by quinones and with potential consequences for the structure and function of selenoproteins. Here, we report data on the interaction of p-benzoquinone (BQ) with the selenoprotein thioredoxin reductase-1 (TrxR1), which exposes an accessible Sec residue upon physiological reduction by NADPH. Our results reveal that BQ targets NADPH-reduced TrxR1 and inhibits its activity using 5,5'-dithiobis(2-nitrobenzoic acid) or juglone as model substrates, consistent with the targeting of both the Cys and Sec residues of TrxR1. In the absence of NADPH, BQ modified the non-catalytic Cys residues, leading to subunit crosslinking, mainly through disulfides, which also resulted in some loss of activity. This crosslinking was time-dependent and independent of the Sec residue. Addition of NADPH after BQ pre-treatment could resolve the disulfide-linked crosslinking. TrxR activity loss was also observed upon incubation of J774A.1 cells or cell lysates with BQ. These data suggest that BQ readily targets TrxR1, albeit in a rather complex manner, which results in structural changes and loss of enzyme activity. We suggest that TrxR1 targeting can explain some of the cytotoxicity of BQ, and potentially also that of other quinone compounds

KW - Quinone

KW - Thioredoxin reductase

KW - Michael addition

KW - Selenocysteine

KW - Selenoprotein

KW - Cysteine

U2 - 10.1016/j.redox.2019.101335

DO - 10.1016/j.redox.2019.101335

M3 - Journal article

C2 - 31590044

VL - 28

JO - Redox Biology

JF - Redox Biology

SN - 2213-2317

M1 - 101335

ER -