Implications for an imidazol-2-yl carbene intermediate in the rhodanase-catalyzed C-S bond formation reaction of anaerobic ergothioneine biosynthesis
Files
Accepted manuscript
Date
2021-03-19
Authors
Cheng, Ronghai
Lai, Rui
Peng, Chao
Lopez, Juan
Li, Zhihong
Naowarojna, Nathchar
Li, Kelin
Wong, Christina
Lee, Norman
Whelan, Stephen A.
Version
Accepted manuscript
OA Version
Citation
R. Cheng, R. Lai, C. Peng, J. Lopez, Z. Li, N. Naowarojna, K. Li, C. Wong, N. Lee, S.A. Whelan, L. Qiao, M.W. Grinstaff, J. Wang, Q. Cui, P. Liu. 2021. "Implications for an imidazol-2-yl carbene intermediate in the rhodanase-catalyzed C-S bond formation reaction of anaerobic ergothioneine biosynthesis.." ACS Catal, Volume 11, Issue 6, pp. 3319 - 3334. https://doi.org/10.1021/acscatal.0c04886
Abstract
In the anaerobic ergothioneine biosynthetic pathway, a rhodanese domain containing enzyme (EanB) activates tne hercynine's sp2 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 sp2 ε-C-H bond and D2O. 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 pKa 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 (EanBWT). 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.