A Rhodanese-Like Enzyme that Catalyzes Desulfination of Ergothioneine Sulfinic Acid

Many actinobacterial species contain structural genes for iron-dependent enzymes that consume ergothioneine by way of O2-dependent dioxygenation. The resulting product ergothioneine sulfinic acid is stable under physiological conditions unless cleavage to sulfur dioxide and trimethyl histidine is catalyzed by a dedicated desulfinase. This report documents that two types of ergothioneine sulfinic desulfinases have evolved by convergent evolution. One type is related to metal-dependent decarboxylases while the other belongs to the superfamily of rhodanese-like enzymes. Pairs of ergothioneine dioxygenases (ETDO) and ergothioneine sulfinic acid desulfinase (ETSD) occur in thousands of sequenced actinobacteria, suggesting that oxidative ergothioneine degradation is a common activity in this phylum.

Structure and Substrate Specificity of S-Methyl Thiourocanate Hydratase

Nicotinamide adenine dinucleotide (NAD+) is a common cofactor in enzyme-catalyzed reactions that involve hydride transfers. In contrast, urocanase and urocanase-like enzymes use NAD+ for covalent electrophilic catalysis. Deciphering avenues by which this unusual catalytic strategy has diversified by evolution may point to approaches for the design of novel enzymes. In this report, we describe the S-methyl thiourocanate hydratase (S-Me-TUC) from Variovorax sp. RA8 as a novel member of this small family of NAD+-dependent hydratases. This enzyme catalyzes the 1,4-addition of water to S-methyl thiourocanate as the second step in the catabolism of S-methyl ergothioneine. The crystal structure of this enzyme in complex with the cofactor and a product analogue identifies critical sequence motifs that explain the narrow and nonoverlapping substrate scopes of S-methyl thiourocanate-, urocanate-, thiourocanate-, and Nτ-methyl urocanate-specific hydratases. The discovery of a S-methyl ergothioneine catabolic pathway also suggests that S-methylation or alkylation may be a significant activity in the biology of ergothioneine.

Enzyme-Catalyzed Oxidative Degradation of Ergothioneine

Ergothioneine is a sulfur-containing metabolite that is produced by bacteria and fungi, and is absorbed by plants and animals as a micronutrient. Ergothioneine reacts with harmful oxidants, including singlet oxygen and hydrogen peroxide, and may therefore protect cells against oxidative stress. Herein we describe two enzymes from actinobacteria that cooperate in the specific oxidative degradation of ergothioneine. The first enzyme is an iron-dependent thiol dioxygenase that produces ergothioneine sulfinic acid. A crystal structure of ergothioneine dioxygenase from Thermocatellispora tengchongensis reveals many similarities with cysteine dioxygenases, suggesting that the two enzymes share a common mechanism. The second enzyme is a metal-dependent ergothioneine sulfinic acid desulfinase that produces Nα-trimethylhistidine and SO2 . The discovery that certain actinobacteria contain the enzymatic machinery for O2 -dependent biosynthesis and O2 -dependent degradation of ergothioneine indicates that these organisms may actively manage their ergothioneine content.

Purification and characterization of 3-(5-oxo-2-thioxoimidazolidin-4-yl) propionic acid desulfhydrase involved in ergothioneine utilization in Burkholderia sp. HME13

Recombinant 3-(5-oxo-2-thioxoimidazolidin-4-yl) propionic acid desulfhydrase (ErtC) derived from Burkholderia sp. HME13 was purified to homogeneity. Here, ErtC's kinetic parameters, optimum reaction temperature and pH, and stability at varying temperatures and pH and the effects of various additives on ErtC activity were determined. Real-time polymerase chain reaction and enzyme assays suggested that ergothioneine induced the expression of ertC.

Characterization of hydantoin-5-propionic acid amidohydrolase involved in ergothioneine utilization in Burkholderia sp. HME13

In our previous study, ertABC genes encoding ergothionase, thiourocanate hydratase, and 3-(5-oxo-2-thioxoimidazolidin-4-yl) propionic acid desulfhydrase were identified, all of which may be involved in ergothioneine utilization of Burkholderia sp. HME13. In this study, we identify the ertD gene encoding metal-dependent hydantoin-5-propionic acid amidohydrolase in this strain. Mn2+-containing ErtD showed maximum activity at 45 °C and pH 8.5 and was stable at temperatures up to 45 °C. The Km and Vmax values of Mn2+-containing ErtD for hydantoin-5-propionic acid were 2.8 m m and 16 U/mg, respectively. Real-time polymerase chain reaction (PCR) revealed that ertD expression levels in Burkholderia sp. HME13 cells cultivated in ergothioneine medium were 3.3-fold higher than those in cells cultivated in Luria-Bertani (LB) medium. ErtD activity in the crude extract from Burkholderia sp. HME13 cells cultured in ergothioneine medium was 0.018 U/mg, whereas that in LB medium was not detected. Accordingly, we suggest that ErtD is involved in ergothioneine utilization in this strain.

Bacterial Degradation of Nτ-Methylhistidine

The first three enzymatic steps by which organisms degrade histidine are universally conserved. A histidine ammonia-lyase (EC 4.3.1.3) catalyzes 1,2-elimination of the α-amino group from l-histidine; a urocanate hydratase (EC 4.2.1.49) converts urocanate to 4-imidazolone-5-propionate, and this intermediate is hydrolyzed to N-formimino-l-glutamate by an imidazolonepropionase (EC 3.5.2.7). Surprisingly, despite broad distribution in many species from all kingdoms of life, this pathway has rarely served as a template for the evolution of other metabolic processes. The only other known pathway with a similar logic is that of ergothioneine degradation. In this report, we describe a new addition to this exclusive collection. We show that the firmicute Bacillus terra and other soil-dwelling bacteria contain enzymes for the degradation of Nτ-methylhistidine to l-glutamate and N-methylformamide. Our results indicate that in some environments, Nτ-methylhistidine can accumulate to concentrations that make its efficient degradation a competitive skill. In addition, this process describes the first biogenic source of N-methylformamide.

In Vitro Reconstitution of a Five-Step Pathway for Bacterial Ergothioneine Catabolism

Ergothioneine is a histidine-derived sulfur metabolite that is biosynthesized by bacteria and fungi. Plants and animals absorb ergothioneine as a micronutrient from their environment or nutrition. Several different mechanisms of microbial ergothioneine production have been described in the past ten years. Much less is known about the genetic and structural basis for ergothioneine catabolism. In this report, we describe the in vitro reconstitution of a five-step pathway that degrades ergothioneine to l-glutamate, trimethylamine, hydrogen sulfide, carbon dioxide, and ammonia. The first two steps are catalyzed by the two enzymes ergothionase and thiourocanate hydratase. These enzymes are closely related to the first two enzymes in histidine catabolism. However, the crystal structure of thiourocanate hydratase from the firmicute Paenibacillus sp. reveals specific structural features that strictly differentiate the activity of this enzyme from that of urocanate hydratases. The final two steps are catalyzed by metal-dependent hydrolases that share most homology with the last two enzymes in uracil catabolism. The early and late part of this pathway are connected by an entirely new enzyme type that catalyzes desulfurization of a thiohydantoin intermediate. Homologous enzymes are encoded in many soil-dwelling firmicutes and proteobacteria, suggesting that bacterial activity may have a significant impact on the environmental availability of ergothioneine.

In Vitro Production of Ergothioneine Isotopologues

Ergothioneine is an emerging component of the redox homeostasis system in human cells and in microbial pathogens, such as Mycobacterium tuberculosis and Burkholderia pseudomallei. The synthesis of stable isotope-labeled ergothioneine derivatives may provide important tools for deciphering the distribution, function, and metabolism of this compound in vivo. We describe a general protocol for the production of ergothioneine isotopologues with programmable ² H, ¹⁵ N, ¹³ C, ³⁴ S, and ³³ S isotope labeling patterns. This enzyme-based approach makes efficient use of commercial isotope reagents and is also directly applicable to the synthesis of radio-isotopologues.

Identification of the gene encoding 3-(5-oxo-2-thioxoimidazolidin-4-yl) propionic acid desulfhydrase in Burkholderia sp. HME13

Here, we report the identification of the gene encoding a novel enzyme, 3-(5-oxo-2-thioxoimidazolidin-4-yl) propionic acid desulfhydrase, in Burkholderia sp. HME13. The enzyme converts 3-(5-oxo-2-thioxoimidazolidin-4-yl) propionic acid and H2O to 3-(2,5-dioxoimidazolidin-4-yl) propionic acid and H2S. Amino acid sequence analysis of the enzyme indicates that it belongs to the DUF917 protein family, which consists of proteins of unknown function.