Conferring specificity in redox pathways by enzymatic thiol/disulfide exchange reactions

Abstract

Thiol-disulfide exchange reactions are highly reversible, displaying nucleophilic substitutions mechanism (S(N)2 type). For aliphatic, low molecular thiols, these reactions are slow, but can attain million times faster rates in enzymatic processes. Thioredoxin (Trx) proteins were the first enzymes described to accelerate thiol-disulfide exchange reactions and their high reactivity is related to the high nucleophilicity of the attacking thiol. Substrate specificity in Trx is achieved by several factors, including polar, hydrophobic, and topological interactions through a groove in the active site. Glutaredoxin (Grx) enzymes also contain the Trx fold, but they do not share amino acid sequence similarity with Trx. A conserved glutathione binding site is a typical feature of Grx that can reduce substrates by two mechanisms (mono and dithiol). The high reactivity of Grx enzymes is related to the very acid pK(a) values of reactive Cys that plays roles as good leaving groups. Therefore, although distinct oxidoreductases catalyze similar thiol–disulfide exchange reactions, their enzymatic mechanisms vary. PDI and DsbA are two other oxidoreductases, but they are involved in disulfide bond formation, instead of disulfide reduction, which is related to the oxidative environment where they are found. PDI enzymes and DsbC are endowed with disulfide isomerase activity, which is related with their tetra-domain architecture. As illustrative description of specificity in thiol-disulfide exchange, redox aspects of transcription activation in bacteria, yeast, and mammals are presented in an evolutionary perspective. Therefore, thiol-disulfide exchange reactions play important roles in conferring specificity to pathways, a required feature for signaling.

Global Transcriptional Response to Organic Hydroperoxide and the Role of OhrR in the Control of Virulence Traits in Chromobacterium violaceum

“…The thioredoxin system operates in parallel with the glutathione-dependent glutaredoxin system to repair thiol groups from oxidation (32,33). Accordingly, upon CHP stress, we detected the upregulation of genes encoding glutathione synthetase enzymes (CV_4275 and CV_4276) and glutathione S-transferases (GSTs) (CV_1164 and CV_2424) (Table S1).…”

“…1B and Table S2). Considering that the synthesis of deoxyribonucleotides by the ribonucleotide reductase NrdAB requires reduction by thioredoxin and glutaredoxin systems (32,33), the downregulation of nucleotide biosynthesis under CHP stress might be a relevant strategy to direct these thiol-disulfide oxidoreductases for the reduction of antioxidant enzymes.…”

Cysteine residues in a yeast viral A/B toxin crucially control host cell killing via pH-triggered disulfide rearrangements

“…Because the deprotonated form of a cysteine represents a nucleophilic thiolate anion, whereas a protonated thiol is chemically less reactive (Jensen et al. , 2009; Netto et al. , 2016), it can be assumed that any cysteine-mediated rearrangement in K28 would be a direct result of pH-driven thiolate anion activation.…”

“…At higher pH, thiols in proteins tend to be deprotonated and become nucleophilic thiolate anions, which can attack one of the sulfur atoms in a disulfide, resulting in disulfide bond rearrangement (Jensen et al. , 2009; Netto et al. , 2016).…”

Special issue on “Free Radical and Redox Biochemistry of Thiols”

“…Different oxido-reductases, such as thioredoxins, glutaredoxins and protein disulfide isomerase, catalyze thioldisulfide exchange reactions by factors of up to 10 6 . The factors conferring specificity in enzymatic thiol/disulfide exchange reactions are reviewed by Netto et al in this issue [14]. Protein-protein interaction during thioldisulfide exchange reactions provides specificity to different pathways.…”