Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China.
Scientific Computing Department, UKRI STFC Daresbury Laboratory, Sci-Tech Daresbury, Warrington WA4 4AD, United Kingdom.
J Chem Inf Model. 2021 Dec 27;61(12):5871-5882. doi: 10.1021/acs.jcim.1c00978. Epub 2021 Nov 22.
Isethionate sulfite-lyase (IseG) is a recently characterized glycyl radical enzyme (GRE) that catalyzes radical-mediated C-S bond cleavage of isethionate to produce acetaldehyde and sulfite. Herein, we use quantum mechanical/molecular mechanical (QM/MM) calculations to investigate the detailed catalytic reaction mechanism of IseG. Our calculations indicate that a previously proposed direct 1,2-elimination mechanism is disfavored. Instead, we suggest a new 1,2-migration mechanism for this enzymatic reaction: a key stepwise 1,2-SO radical migration occurs after the catalytically active cysteinyl radical grabs a hydrogen atom from isethionate, followed by hydrogen atom transfer from cysteine to a 1-hydroxylethane-1-sulfonate radical intermediate. Finally, the elimination of sulfite from 1-hydroxylethane-1-sulfonate to result in the final product is likely to occur outside the enzyme. Glu468 in the active site is found to help orient the substrate rather than grabbing a proton from the hydroxyl group of the substrate. Our findings help reveal the mechanisms of radical-mediated C-S bond cleavage of organosulfonates catalyzed by GREs and expand the understanding of radical-based enzymatic catalysis.
亚磺酸盐-亚硫酸氢盐裂解酶（IseG）是一种最近被描述的甘氨酰基自由基酶（GRE），它能催化亚磺酸盐的自由基介导的 C-S 键断裂，生成乙醛和亚硫酸盐。在此，我们使用量子力学/分子力学（QM/MM）计算来研究 IseG 的详细催化反应机制。我们的计算表明，以前提出的直接 1,2-消除机制是不利的。相反，我们提出了这种酶促反应的一种新的 1,2-迁移机制：在催化活性半胱氨酸自由基从亚磺酸盐中攫取一个氢原子后，发生关键的分步 1,2-SO 自由基迁移，然后从半胱氨酸向 1-羟乙磺酸自由基中间体转移氢原子。最后，亚硫酸盐从 1-羟乙磺酸中消除生成最终产物很可能发生在酶之外。在活性位点的Glu468 被发现有助于定向底物，而不是从底物的羟基上攫取质子。我们的发现有助于揭示 GRE 催化的有机磺酸盐的自由基介导的 C-S 键断裂机制，并扩展对基于自由基的酶催化的理解。
