Alkylcysteine Sulfoxide C–S Monooxygenase Uses a Flavin-Dependent Pummerer Rearrangement

Abstract

Flavoenzymes are highly versatile and participate in the catalysis of a wide range of reactions, including key reactions in the metabolism of sulfur-containing compounds. S-Alkyl cysteine is formed primarily by the degradation of S-alkyl glutathione generated during electrophile detoxification. A recently discovered S-alkyl cysteine salvage pathway uses two flavoenzymes (CmoO and CmoJ) to dealkylate this metabolite in soil bacteria. CmoO catalyzes a stereospecific sulfoxidation, and CmoJ catalyzes the cleavage of one of the sulfoxide C–S bonds in a new reaction of unknown mechanism. In this paper, we investigate the mechanism of CmoJ. We provide experimental evidence that eliminates carbanion and radical intermediates and conclude that the reaction proceeds via an unprecedented enzyme-mediated modified Pummerer rearrangement. The elucidation of the mechanism of CmoJ adds a new motif to the flavoenzymology of sulfur-containing natural products and demonstrates a new strategy for the enzyme-catalyzed cleavage of C–S bonds.

DszA Catalyzes C–S Bond Cleavage through N5–Hydroperoxyl Formation

“…Our results corroborate that the existence of a hydrophobic O 2 pocket at the re -side of FMN in flavin containing enzymes, which catalyze oxygenase reactions, leads to the formation of a N 5 OOH intermediate instead of the better known C 4a OOH. This further highlights the importance of the N 5 position in flavin-catalyzed oxygenase reactions, as the one conducted by DszA, as observed by other authors, 69 and in particular for flavin-mediated C–S bond cleavage as also demonstrated by Hazra and Begley, 70 which recently elucidated a novel catalytic reaction of the flavin monooxygenase CmoJ that also involves N 5 -hydroperoxyl formation, and by Wu and Chen, which proposed that C–S bond cleavage catalyzed by MsuD requires a N5OO – intermediate. 71 …”