Abstract
Ergothioneine is a histidine thio-derivative isolated in 1909. In ergothioneine biosynthesis, the combination of a mononuclear non-heme iron enzyme catalyzed oxidative C-S bond formation reaction and a PLP-mediated C-S lyase (EgtE) reaction results in a net sulfur transfer from cysteine to histidine side-chain. This demonstrates a new sulfur transfer strategy in the biosynthesis of sulfur-containing natural products. Due to difficulties associated with the overexpression of Mycobacterium smegmatis EgtE protein, the proposed EgtE functionality remained to be verified biochemically. In this study, we have successfully overexpressed and purified M. smegmatis EgtE enzyme and evaluated its activities under different in vitro conditions: C-S lyase reaction using either thioether or sulfoxide as a substrate in the presence or absence of reductants. Results from our biochemical characterizations support the assignment of sulfoxide 4 as the native EgtE substrate and the involvement of a sulfenic acid intermediate in the ergothioneine C-S lyase reaction.
Highlights
Glutathione, one of the most abundant natural thiols inside the cells, plays a key role in buffering the intracellular redox-state
We sub-cloned M. smegmatis EgtE gene into the pASK-IBA3+ vector and the protein was overexpressed in the E. coli BL21(DE3) strain
We proposed that a sulfenic acid intermediate (12, Fig. 5) is involved when sulfoxide 4 is used as substrate
Summary
Glutathione, one of the most abundant natural thiols inside the cells (up to 10 mM), plays a key role in buffering the intracellular redox-state. 1H-NMR spectrum of EgtE reactions using either thio-ether 8 or sulfoxide 4 as the substrate. When the EgtE reactions using either thio-ether 8 or sulfoxide 4 as substrate were compared, the difference in sulfur oxidation state suggests that redox-chemistries must be considered in order to explain the formation of ergothioneine and ergothioneine-2-sulfinic acid (14).
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