Mechanistic Studies of the Radical S- Adenosyl- l -methionine Enzyme 4-Demethylwyosine Synthase Reveal the Site of Hydrogen Atom Abstraction

TYW1 catalyzes the formation of 4-demethylwyosine via the condensation of N-methylguanosine (m¹G) with carbons 2 and 3 of pyruvate. In this study, labeled transfer ribonucleic acid (tRNA) and pyruvate were utilized to determine the site of hydrogen atom abstraction and regiochemistry of the pyruvate addition. tRNA containing a ²H-labeled m¹G methyl group was used to identify the methyl group of m¹G as the site of hydrogen atom abstraction by 5′-deoxyadenosyl radical. [2-¹³C₁-3,3,3-²H₃]Pyruvate was used to demonstrate retention of all the pyruvate protons, indicating that C2 of pyruvate forms the bridging carbon of the imidazoline ring and C3 the methyl.