High Production of Ergothioneine in Escherichia coli using the Sulfoxide Synthase from Methylobacterium strains

We previously constructed a heterologous production system for ergothioneine (ERG) in Escherichia coli using five ERG biosynthesis genes (egtABCDE) from Mycobacterium smegmatis. However, significant amounts of hercynine (HER), an intermediate of ERG, as ERG were accumulated, suggesting that the reaction of EgtB catalyzing the attachment of gamma-glutamylcysteine (gamma GC) to HER to yield hercynyl-gamma-glutamylcysteine sulfoxide was a bottleneck. In this study, we searched for other EgtBs and found many egtB orthologs in diverse microorganisms. Among these, Methylobacterium strains possessed EgtBs that catalyze the direct conversion of HER into hercynylcysteine sulfoxide with L-cysteine (L-Cys) as a sulfur donor, in a manner similar to those of acidobacterial CthEgtB and fungal Egt1. An in vitro study with recombinant EgtBs from Methylobacterium brachiatum and Methylobacterium pseudosasicola clearly showed that both enzymes accepted L-Cys but not gamma GC. We reconstituted the ERG production system in E. coli with egtB from M. pseudosasicola; ERG productivity reached 657 mg L-1.