Evidence of Diradicals Involved in the Yeast Transketolase Catalyzed Keto‐Transferring Reactions. (18th October 2018)

• Record Type: Journal Article
• Authors: Hsu, Ning‐Shian; Wang, Yung‐Lin; Lin, Kuan‐Hung; Chang, Chi‐Fon; Ke, Shyue‐Chu; Lyu, Syue‐Yi; Hsu, Li‐Jen; Li, Yi‐Shan; Chen, Sheng‐Chia; Wang, Kuei‐Chen; Li, Tsung‐Lin
• Is Part Of: Chembiochem. Volume 19:Number 22(2018)
• Page Start: 2395
• Page End: 2402
• Publication Date: 2018-10-18
• Subjects: C−C coupling -- electron transfer -- enzyme catalysis -- radical reactions -- reaction mechanisms; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pharmaceutical chemistry -- Periodicals; 572
• DOI: 10.1002/cbic.201800378
• Languages: English
• ISSNs: 1439-4227

Abstract

Abstract: Transketolase (TK) catalyzes a reversible transfer of a two‐carbon (C2 ) unit between phosphoketose donors and phosphoaldose acceptors, for which the group‐transfer reaction that follows a one‐ or two‐electron mechanism and the force that breaks the C2"−C3" bond of the ketose donors remain unresolved. Herein, we report ultrahigh‐resolution crystal structures of a TK (TKps) from Pichia stipitis in previously undiscovered intermediate states and support a diradical mechanism for a reversible group‐transfer reaction. In conjunction with MS, NMR spectroscopy, EPR and computational analyses, it is concluded that the enzyme‐catalyzed non‐Kekulé diradical cofactor brings about the C2"−C3" bond cleavage/formation for the C2 ‐unit transfer reaction, for which suppression of activation energy and activation and destabilization of enzymatic intermediates are facilitated. Abstract : Moving C2 units : Transketolase from P. stipitis catalyzes a reversible C2 ‐transfer radical mechanism, in which the thiamine diphosphate cofactor is subject to enzyme‐catalyzed isomerization to form non‐Kekulé diradicals required for bond cleavage/formation because of suppression of the activation energy and activation and destabilization of intermediates.