Structure of the Sulfoxide Synthase EgtB from the Ergothioneine Biosynthetic Pathway

Abstract

The non-heme iron enzyme EgtB catalyzes O2 -dependent C-S bond formation between γ-glutamyl cysteine and N-α-trimethyl histidine as the central step in ergothioneine biosynthesis. Both, the catalytic activity and the architecture of EgtB are distinct from known sulfur transferases or thiol dioxygenases. The crystal structure of EgtB from Mycobacterium thermoresistibile in complex with γ-glutamyl cysteine and N-α-trimethyl histidine reveals that the two substrates and three histidine residues serve as ligands in an octahedral iron binding site. This active site geometry is consistent with a catalytic mechanism in which C-S bond formation is initiated by an iron(III)-complexed thiyl radical attacking the imidazole ring of N-α-trimethyl histidine.

Heteroatom–Heteroatom Bond Formation in Natural Product Biosynthesis

“…563,567 The crystal structure of EgtB from Mycobacterium thermoresistibile has been solved which has provided insight into this coupled S -oxygenation/C–S bond forming reaction. 568 Three structures were obtained, including the apo protein, the protein in complex with Fe II and 235 , and the protein in complex with manganese, N -α-dimethyl histidine (DMH) and γGC. Interestingly, although the enzyme contains the conserved 2-His-1-carboxylate motif predicted to bind iron, these crystal structures revealed an unusual binding mode involving three histidine residues coordinating to the iron center.…”

Conservation of the C-type lectin fold for accommodating massive sequence variation in archaeal diversity-generating retroelements

“…Mtd has a C-type lectin (CLec)-fold, and in particular belongs to the formylglycine-generating enzyme (FGE) subclass of the CLec-fold [14]. The CLec-fold is a general ligand-binding motif [15], but can also have enzymatic functionality as seen in FGE [16] and in sulfoxide synthase [17]. The only other structurally characterized DGR variable protein, TvpA from the spirochete Treponema denticola , also has an FGE-type CLec-fold [14].…”

Go it alone: four-electron oxidations by mononuclear non-heme iron enzymes

“…Surprisingly, when the crystal structure of EgtB was determined, the active site iron was coordinated by a 3-His facial triad rather than the anticipated 2-His-1-Glu ligand set [95]. As mentioned previously, the 3-His facial triad coordination sphere has been observed in only a handful of enzymes, including Dke1 [96] and CDO [69], further underscoring mechanistic similarities between these enzymes and the TDOs.…”