Molybdopterin biosynthesis: Trapping an unusual purine ribose adduct in the MoaA-catalyzed reaction

MoaA/MoaC catalyze a remarkable rearrangement reaction in which guanosine-5′-triphosphate (GTP) is converted to cyclic pyranopterin monophosphate (cPMP). In this reaction, the C8 of GTP is inserted between the C2′ and the C3′ carbons of the GTP ribose. Previous experiments with GTP isotopomers demonstrated that the ribose C3′ hydrogen atom is abstracted by the adenosyl radical. This led to a novel mechanistic proposal involving an intermediate with a bond between the C8 of guanine and C3′ of the ribose. This paper describes the use of 2′,3′-dideoxyGTP to trap this intermediate.