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Single-Step Replacement of an Unreactive C–H Bond by a C–S Bond Using Polysulfide as the Direct Sulfur Source in the Anaerobic Ergothioneine Biosynthesis
journal contribution
posted on 2020-07-30, 14:18 authored by Ronghai Cheng, Lian Wu, Rui Lai, Chao Peng, Nathchar Naowarojna, Weiyao Hu, Xinhao Li, Stephen A. Whelan, Norman Lee, Juan Lopez, Changming Zhao, Youhua Yong, Jiahui Xue, Xuefeng Jiang, Mark W. Grinstaff, Zixin Deng, Jiesheng Chen, Qiang Cui, Jiahai Zhou, Pinghua LiuErgothioneine,
a natural longevity vitamin and antioxidant, is
a thiol-histidine derivative. Recently, two types of biosynthetic
pathways were reported. In the aerobic ergothioneine biosyntheses,
non-heme iron enzymes incorporate a sulfoxide into an sp2 C–H bond from trimethyl-histidine (hercynine) through oxidation
reactions. In contrast, in the anaerobic ergothioneine biosynthetic
pathway in a green-sulfur bacterium, Chlorobium limicola, a rhodanese domain containing protein (EanB), directly replaces
this unreactive hercynine C–H bond with a C–S bond.
Herein, we demonstrate that polysulfide (HSSnSR) is the direct sulfur source in EanB catalysis. After identifying
EanB’s substrates, X-ray crystallography of several intermediate
states along with mass spectrometry results provide additional mechanistic
details for this reaction. Further, quantum mechanics/molecular mechanics
(QM/MM) calculations reveal that the protonation of Nπ of hercynine by Tyr353 with the assistance of Thr414 is a key activation
step for the hercynine sp2 C–H bond in this trans-sulfuration
reaction.
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hercyninenon-heme iron enzymesmass spectrometry resultsDirect Sulfur SourcebondAnaerobic Ergothioneine Biosynthesi...longevity vitaminsulfur sourceergothioneine biosynthetic pathwayTyr 353Chlorobium limicolaSingle-Step ReplacementEanB catalysisThr 414HSS n SRtrans-sulfuration reactionactivation stepgreen-sulfur bacteriumX-ray crystallographyergothioneine biosynthesesbiosynthetic pathwaysN πoxidation reactionsrhodanese domainBondQM