Discovery of a thiamin-utilizing α-keto acid decarboxylase ribozyme: Implications for RNA’s role in primordial metabolism

Vitamins are hypothesized to be relics of an RNA World, and likely participants in an RNA-mediated primordial metabolism. If catalytic RNAs could harness vitamin cofactors to aid their function, in a manner similar to enzymes, it would enable ribozymes to catalyze a much larger set of chemical reactions. The cofactor thiamin diphosphate, a derivative of vitamin B1 (thiamin), is used by enzymes to catalyze difficult metabolic reactions, including decarboxylation of stable α-keto acids such as pyruvate. Here I report a ribozyme that uses free thiamin to decarboxylate a pyruvate-based suicide substrate (LnkPB). Thiamin conjugated to biotin was used to isolate catalytic individuals from a pool of random sequence RNAs attached to LnkPB. Analysis of a stable guanosine adduct obtained via digestion of an RNA sequence (clone dc4) showed the expected decarboxylation product. Discovery of a prototypic thiamin-utilizing ribozyme has implications for RNA's role in orchestrating early metabolic cycles.