A Selenium-for-Oxygen Swapping Reaction Catalyzed by the Radical S-Adenosyl Methionine Enzyme AbmM.

Selenium is an essential element to organisms; however, few enzymes are known to catalyze the carbon-selenium bond formation. While several carbon-sulfur bond-forming enzymes have been engineered to install carbon-selenium bonds by using paired electron chemistry, the potential of utilizing radical chemistry to facilitate C-Se bond formation is underdeveloped. Herein, the native sulfur-inserting radical S-adenosyl methionine (SAM) enzyme AbmM involved in the biosynthesis of albomycin δ2 is shown to catalyze a selenium-for-oxygen swapping reaction converting the furanose of cytidine 5'-diphosphate to a 4'-hydroxy-4'-selenofuranose diphosphate. The dephosphorylated 4'-seleno product can be further processed by downstream biosynthetic enzymes AbmG and AbmH to yield a 4'-selenoheptose nucleoside. These results establish an enzymatic approach to synthesize 4'-seleno sugars in a radical-mediated manner and provide a likely route to prepare selenium-containing analogues of albomycin δ2 for drug discovery. This work also demonstrates that [Fe4Se4] clusters can support radical SAM redox chemistry and that the radical SAM cluster in AbmM can function as the chalcogen donor.