Ablation of the mammalian methionine sulfoxide reductase A affects the expression level of cysteine deoxygenase Derek B. Oien, Jackob Moskovitz * University of Kansas, School of Pharmacy, Department of Pharmacology and Toxicology, Lawrence, KS 66045, USA Received 1 November 2006 Available online 20 November 2006 Abstract Methionine sulfoxide reductases (Msrs) are able to reduce methionine sulfoxide to methionine both in proteins and free amino acids. By their action it is possible to regulate the function of specific proteins and the cellular antioxidant defense against oxidative damage. Similarly, cysteine deoxygenase (CDO) may be involved in the regulation of protein function and antioxidant defense mechanisms by its ability to oxidized cysteine residues. The two enzymes’ involvement in sulfur amino-acids metabolism seems to be connected. Lack of methionine sulfoxide reductase A (MsrA) in liver of MsrA À / À led to a significant drop in the cellular level of thiol groups and lowered the CDO level of expression. Moreover, following selenium deficient diet (applied to decrease the expression levels of selenoproteins like MsrB), the latter effect was maintained while the basal levels of thiol decreased in both mouse strains. We suggest that both enzymes are working in coordination to balance cellular antioxidant defense. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Cysteine deoxygenase; Thiol groups; Sulfur amino acids; Oxidative stress; Post-translation modification Oxidation of methionine (either as free amino acid as protein-residue) can be readily reversed by the methionine sulfoxide reductase system (Msr), comprised of MsrA and MsrB [1]. Methionine sulfoxide (MetO) has two forms: S-MetO and R-MetO that are reduced to methionine by MsrA and MsrB, respectively [2,3]. Knocking-out the gene for MsrA causes deficiency in antioxidant defense, accumu- lating of oxidized proteins, and shorter life span in various organisms [1] including bacteria, [4] yeast [5], and mouse [6]. The enzyme cysteine deoxygenase (CDO) catalyzes the oxidation of Cysteine to cysteine sulfinic acid while using Fe 2+ as a cofactor in mammals and yeast. The activ- ity of CDO plays an important role in cysteine catabolism, taurine synthesis, and accumulation of pyruvate and sul- fate [7–9]. The special significance of taurine synthesis, mediated by CDO, is mainly due to its involvement in bile salt synthesis, cardiac function, and protection of neuronal cells from ischemia-induced damage [10–12]. It has been suggested that cysteine may act on the N-methyl-D-aspar- tate subtype of glutamate receptor [13] and/or be involved in the formation of reactive oxygen species (ROS) that in- turn oxidize other molecules, like dopamine [14]. The Msr system plays a key role in protecting cells from oxidative damage as well as repairing methionine-oxidized proteins by the system’s components that use thiol groups for their activities. The cellular levels of the sulfur amino-acids cys- teine and methionine regulate the expression level of CDO [7]. Thus, in the absence of MsrA, it is predicted that enhanced oxidation of cysteine and methionine will occur and thereby cause changes in cysteine metabolism and CDO expression. Consequently, the effect of MsrA abla- tion on CDO and free and protein-bound thiol levels were investigated. Both MsrA and CDO are highly expressed in liver; therefore we have used the livers of MsrA À / À and wild-type control mice for the various analyses. Addition- ally, we have analyzed the ability of CDO to affect the activity of MsrA, using pure recombinant proteins of both enzymes. 0006-291X/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2006.11.063 * Correspondent author. Fax: +1 785 864 5219. E-mail address: moskovij@ku.edu (J. Moskovitz). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 352 (2007) 556–559 BBRC