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. 2018 Feb 20;28(6):431–444. doi: 10.1089/ars.2017.7300

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© Bridgette M. Cumming, et al., 2018; Published by Mary Ann Liebert, Inc.

This article is available under the Creative Commons License CC-BY-NC (http://creativecommons.org/licenses/by-nc/4.0). This license permits non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited. Permission only needs to be obtained for commercial use and can be done via RightsLink.

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FIG. 4. — Biosynthetic pathways of EGT in (A) mycobacteria and (B) N. crassa and other fungi. (A) In mycobacteria, EGT biosynthesis occurs through five enzymatic steps where L-histidine is methylated into hercynine by methyltransferase (EgtD), followed by formation of a hercynyl γ-glutamylcysteine sulfoxide intermediate after addition of γ-glutamylcysteine by a formylglycine-generating enzyme-like protein (EgtB). Glutamate is removed from this intermediate by a glutamine amidotransferase (EgtC) to form hercynlcysteine sulfoxide that is converted into ergothioneine by a pyridoxal 5-phosphate-dependent β-lyase (EgtE). EgtA is a γ-glutamyl cysteine synthetase. (B) In N. crassa, EGT is synthesized with two enzymes: Egt1 methylates histidine and forms the C-S bond with cysteine to form hercynylcysteine sulfoxide; and Egt2 cleaves the C-S bond to form ergothioneine.