| Catharanthus roseus produces vinblastine and vincristine, monoterpenoid indole alkaloids that are clinically effective anticancer agents. As part of an investigation into the biosynthesis of secologanin, the terpenoid precursor for these alkaloids, we have purified and characterized the enzyme that oxidizes 10-hydroxygeraniol to 10-oxygeranial using NADP+ as a cofactor. This activity, which we called 10-hydroxygeraniol oxidoreductase (Cr10HGO), is usually undetectable in plants that do not produce monoterpene indole alkaloids. Nevertheless, protein sequencing of the purified enzyme revealed that the enzyme has a high overall sequence similarity to many zinc-containing long chain alcohol dehydrogenases, including mannitol dehydrogenase (MTD) from celery, an elicitable MTD from parsley and Arabidopsis, and a wound-inducible MTD from alfalfa. Studies on recombinant enzyme expressed from a cDNA in E. coli showed that Cr10HGO is a novel alcohol dehydrogenase with a preference for monoterpene primary alcohols containing allylic double bonds, but little or no activity against typical substrates for MTDs. These results suggest that Cr10HGO is a member of the MTD gene family that has acquired novel expression pattern and substrate specificity and has been recruited to the monoterpenoid indole alkaloid pathway. |
