Discovery of the selenium-containing antioxidant ovoselenol derived from convergent evolution

Selenium is an essential micronutrient, but its presence in biology has been limited to protein and nucleic acid biopolymers. The recent identification of a biosynthetic pathway for selenium-containing small molecules suggests that there is a larger family of selenometabolites that remains to be discovered. Here we identify a recently evolved branch of abundant and uncharacterized metalloenzymes that we predict are involved in selenometabolite biosynthesis using a bioinformatic search strategy that relies on the mapping of composite active site motifs. Biochemical studies confirm this prediction and show that these enzymes form an unusual C–Se bond onto histidine, thus giving rise to a distinct selenometabolite and potent antioxidant that we have termed ovoselenol. Aside from providing insights into the evolution of this enzyme class and the structural basis of C–Se bond formation, our work offers a blueprint for charting the microbial selenometabolome in the future. Although biosynthetic pathways of selenium-containing macromolecules have been known for decades, pathways for specific incorporation of selenium into small molecules have only recently begun to be uncovered. Now the selenometabolome is expanded further through the discovery and biosynthetic elucidation of ovoselenol, a selenium-containing antioxidant found in marine microorganisms.