Identification of a novel enzyme and the regulation of key enzymes in mammalian taurine synthesis.

Taurine has many pharmacological roles on various tissues. The maintenance of abundant taurine content in the mammalian body through endogenous synthesis, in addition to exogenous intake, is the essential factor for morphological and functional maintenances in most tissues. The synthesis of taurine from sulfur-containing amino acids is influenced by various factors. Previous literature findings indicate the influence of the intake of proteins and sulfur-containing amino acids on the activity of the rate-limiting enzymes cysteine dioxygenase and cysteine sulfinate decarboxylase. In addition, the regulation of the activity and expression of taurine-synthesis enzymes by hormones, bile acids, and inflammatory cytokines through nuclear receptors have been reported in liver and reproductive tissues. Furthermore, flavin-containing monooxygenase subtype 1 was recently identified as the taurine-synthesis enzyme that converts hypotaurine to taurine. This review introduces the novel taurine synthesis enzyme and the nuclear receptor-associated regulation of key enzymes in taurine synthesis.

Cleavage of a carbon-fluorine bond by an engineered cysteine dioxygenase.

Cysteine dioxygenase (CDO) plays an essential role in sulfur metabolism by regulating homeostatic levels of cysteine. Human CDO contains a post-translationally generated Cys93-Tyr157 cross-linked cofactor. Here, we investigated this Cys-Tyr cross-linking by incorporating unnatural tyrosines in place of Tyr157 via a genetic method. The catalytically active variants were obtained with a thioether bond between Cys93 and the halogen-substituted Tyr157, and we determined the crystal structures of both wild-type and engineered CDO variants in the purely uncross-linked form and with a mature cofactor. Along with mass spectrometry and 19F NMR, these data indicated that the enzyme could catalyze oxidative C-F or C-Cl bond cleavage, resulting in a substantial conformational change of both Cys93 and Tyr157 during cofactor assembly. These findings provide insights into the mechanism of Cys-Tyr cofactor biogenesis and may aid the development of bioinspired aromatic carbon-halogen bond activation.

Addition of an external electron donor to in vitro assays of cysteine dioxygenase precludes the need for exogenous iron.

Cysteine dioxygenase (CDO) utilizes a 3-His facial triad for coordination of its metal center. Recombinant CDO present in cellular lysate exists primarily in the ferrous form and exhibits significant catalytic activity. Removal of CDO from the reducing cellular environment during purification results in the loss of bound iron and oxidation of greater than 99% of the remaining metal centers. The as-isolated recombinant enzyme has comparable activity as the background level of L-cysteine oxidation confirming that CDO is inactive under the aerobic conditions required for catalysis. Including exogenous ferrous iron in assays resulted in non-enzymatic product formation; however, addition of an external reductant in assays of the purified protein resulted in the recovery of CDO activity. EPR spectroscopy of CDO in the presence of a reductant confirms that the recovered activity is consistent with reduction of iron to the ferrous form. The as-isolated enzyme in the presence of L-cysteine was nearly unreactive with the dioxygen analog, but had increased affinity when pre-incubated with an external reductant. These studies shed light on the discrepancies among reported kinetic parameters for CDO and also juxtapose the stability of the 3-His and 2-His/1-carboxylate ferrous enzymes in the presence of dioxygen.

Sézary syndrome is a unique cutaneous T-cell lymphoma as identified by an expanded gene signature including diagnostic marker molecules CDO1 and DNM3.

Sezary syndrome (SS) is a rare, aggressive CD4+ cutaneous T-cell lymphoma (CTCL); molecular traits differentiating SS from nonleukemic mycosis fungoides (MF) and from inflammatory skin diseases (ID) are not sufficiently characterized. Peripheral blood mononuclear cells (PBMC) of 10 SS patients and 10 healthy donors (HD) were screened by Affymetrix U133Plus2.0 chips for differential gene expression. Ten candidate genes were confirmed by qRT-PCR to be significantly overexpressed in CD4+ T cells of SS versus HD/ID. For easier clinical use, these genes were re-analyzed in PBMC; qRT-PCR confirmed five novel (DNM3, IGFL2, CDO1, NEDD4L, KLHDC5) and two known genes (PLS3, TNFSF11) to be significantly overexpressed in SS. Multiple logistic regression analysis revealed that CDO1 and DNM3 had the highest discriminative power in combination. Upon comparison of PBMC and skin samples of SS versus MF, CDO1 and DNM3 were found upregulated only in SS. Using anti-CDO1 antisera, differential expression of CDO1 protein was confirmed in SS CD4+ T cells. Interestingly, DNM3 and CDO1 are known to be regulated by SS-associated transcription factors TWIST1 and c-myb, respectively. Furthermore, CDO1 catalyzes taurine synthesis and taurine inhibits apoptosis and promotes chemoprotection. In summary, CDO1 and DNM3 may improve the diagnosis of SS and open novel clues to its pathogenesis.

Induction of cysteine dioxygenase activity by oral administration of cysteine analogues to the rat: implications for drug efficacy and safety.

One of the major steps in the oxidation of the sulphur-containing amino acid, L-cysteine, is the production of cysteine sulphinic acid, catalysed by the enzyme cysteine dioxygenase. This enzyme plays a key role in the intermediary metabolism of sulphur-containing compounds. The activity of this crucial enzyme is known to be influenced by sulphur-compound intake, being increased in animals fed an excess of L-cysteine or methionine. However, the affects on this enzyme of the chronic administration of drugs similar in structure to cysteine are unknown. This has now been investigated using the anti-rheumatic agent, D-penicillamine, and the mucoactive compound, S-carboxymethyl-L-cysteine. Repeated oral administration of these sulphur-containing drugs to male Wistar rats for five consecutive days led to a significant increase in hepatic cysteine dioxygenase activity. This increase in the production rate of cysteine sulphinic acid remained evident until returning to control levels four days after cessation of drug administration. These observations provide evidence that these two drugs interact with the intermediary biochemistry of sulphur compounds and may provide hitherto unappreciated insights into mechanisms by which therapeutic effects and adverse reactions may occur.