Open AccessImplications for an Imidazole-2-yl Carbene Intermediate in the Rhodanase-Catalyzed C–S Bond Formation Reaction of Anaerobic Ergothioneine Biosynthesis
Author(s) -
Ronghai Cheng,
Rui Lai,
Chao Peng,
Juan Lopez,
Zhihong Li,
Nathchar Naowarojna,
Kelin Li,
Christina Wong,
Norman Lee,
Stephen A. Whelan,
Lu Qiao,
Mark W. Grinstaff,
Jiangyun Wang,
Qiang Cui,
Pinghua Liu
Publication year - 2021
Publication title -
acs catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.898
H-Index - 198
ISSN - 2155-5435
DOI - 10.1021/acscatal.0c04886
Subject(s) - carbene , chemistry , ergothioneine , catalysis , stereochemistry , deuterium , biocatalysis , imidazole , medicinal chemistry , reaction mechanism , organic chemistry , antioxidant , physics , quantum mechanics
In the anaerobic ergothioneine biosynthetic pathway, a rhodanese domain containing enzyme (EanB) activates tne hercynine's sp 2 ε-C-H Dona ana replaces it with a C-S bond to produce ergothioneine. The key intermediate for this trans-sulfuration reaction is the Cys412 persulfide. Substitution of the EanB-Cys412 persulfide with a Cys412 perselenide does not yield the selenium analog of ergothioneine, selenoneine. However, in deuterated buffer, the perselenide-modified EanB catalyzes the deuterium exchange between hercynine's sp 2 ε-C-H bond and D 2 O. Results from QM/MM calculations suggest that the reaction involves a carbene intermediate and that Tyr353 plays a key role. We hypothesize that modulating the pK a of Tyr353 will affect the deuterium-exchange rate. Indeed, the 3,5-difluoro tyrosine containing EanB catalyzes the deuterium exchange reaction with k ex of ~10-fold greater than the wild-type EanB (EanB WT ). With regards to potential mechanisms, these results support the involvement of a carbene intermediate in EanB-catalysis, rendering EanB as one of the few carbene-intermediate involving enzymatic systems.