Site directed mutagenesis of Catharanthus roseus (+)-vincadifformine 19-hydroxylase (CYP71BY3) results in two distinct enzymatic functions

The most abundant monoterpenoid indole alkaloids (MIAs) in Catharanthus roseus roots include lochnericine and (+)-echitovenine. The formation of (+)-echitovenine involves a 3-step pathway including (+)-vincadifformine-19-hydroxylase (V19H) that differentiates it from a parallel pathway involved in the formation of lochnericine, hörhammericine and its O-acetylated derivative. Homology based modeling and docking experiments in the present study show that (+) and (−) vincadifformine can occupy the V19H active site and is proven experimentally by showing that (−)-vincadifformine is a competitive inhibitor of V19H. Comparative modeling of V19H with tabersonine 3-oxidase (T3O) and tabersonine 19-hydroxylase (T19H) that accept (−)-aspidosperma MIAs identified four conserved amino acid residues in T3O and T19H that were different in the V19H binding site and were used to generate a series of single-, double-, or four-point mutations in V19H. While all mutants retained their ability to convert (+)-vincadifformine to (+)-minovincinine only the four-point mutant gained T3O activity enabling it to convert (−)-tabersonine to tabersonine 2,3-epoxide. The gain of T3O-like activity following mutagenesis without the loss of V19H activity supports the hypothesis that V19H shares a common ancestor to T3O which is involved in vindoline biosynthesis in C. roseus leaves.