Protein redox modification as a cellular defense mechanism against tissue ischemic injury

Abstract

Protein oxidative or redox modifications induced by reactive oxygen species (ROS) or reactive nitrogen species (RNS) not only can impair protein function, but also can regulate and expand protein function under a variety of stressful conditions. Protein oxidative modifications can generally be classified into two categories: irreversible oxidation and reversible oxidation. While irreversible oxidation usually leads to protein aggregation and degradation, reversible oxidation that usually occurs on protein cysteine residues can often serve as an "on and off" switch that regulates protein function and redox signaling pathways upon stress challenges. In the context of ischemic tolerance, including preconditioning and postconditioning, increasing evidence has indicated that reversible cysteine redox modifications such as S-sulfonation, S-nitrosylation, S-glutathionylation, and disulfide bond formation can serve as a cellular defense mechanism against tissue ischemic injury. In this review, I highlight evidence of cysteine redox modifications as protective measures in ischemic injury, demonstrating that protein redox modifications can serve as a therapeutic target for attenuating tissue ischemic injury. Prospectively, more oxidatively modified proteins will need to be identified that can play protective roles in tissue ischemic injury, in particular, when the oxidative modifications of such identified proteins can be enhanced by pharmacological agents or drugs that are available or to be developed.

Figure 1

Classification of protein oxidative modifications into two categories: irreversible oxidation and reversible oxidation. *Note: only a few studies so far have reported that sulfinic acid (S-sulfinition) formation could be reversible [180, 181].

Figure 2

Reversible cysteine modification products that are widely studied. These products include S-sulfenation (sulfenic acid, –SOH), S-nitrosylation (–SNO), S-glutathionylation (–P–S–S–G), and either intra- or interdisulfides.

Figure 3

Analysis of reversible cysteine redox modifications. What is shown is a one of the popular methods generally called a “biotin switch” assay, which involves alkylating the free thiol groups (step 1), reducing the modified cysteine residues using specific reductant for each oxidation product (step 2), and relabeling of the newly generated free thiol groups using biotin conjugated probes (step 3). Following biotinylation, the samples can be further analyzed by either western blot (step 5) or affinity purification (step 4). Note that protein sulfenic acids can be directly labeled by dimedone conjugated biotin probes as described in the text.