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Structure and mechanism of ergothionase from Treponema denticola.

Ergothioneine is a sulfur-containing histidine derivative that emerges from microbial biosynthesis and enters the human body via intestinal uptake and regulated distribution into specific tissues. While the proteins involved in biosynthesis and uptake are well characterized, less is known about the degradative pathways of ergothioneine. In this report we describe the crystal structure of the active form of ergothionase from the oral pathogen Treponema denticola in complex with the substrate analog desmethyl-ergothioneine sulfonic acid. This enzyme catalyzes 1,2-elimination of trimethylamine from ergothioneine and its oxidation product ergothioneine sulfonic acid using a unique mode of substrate activation combined with acid/base catalysis. This structural and mechanistic investigation revealed four essential catalytic residues that are strictly conserved in homologous proteins from common gastrointestinal bacteria and numerous pathogenic bacteria, suggesting that bacterial activity may play an important role in determining the availability of ergothioneine in healthy and diseased human tissue.