Nectrisine Biosynthesis Genes in Thelonectria discophora SANK 18292: Identification and Functional Analysis

The fungus Thelonectria discophora SANK 18292 produces the iminosugar nectrisine, which has a nitrogen-containing heterocyclic 5-membered ring and acts as a glycosidase inhibitor. In our previous study, an oxidase (designated NecC) that converts 4-amino-4-deoxyarabinitol to nectrisine was purified from T. discophora cultures. However, the genes required for nectrisine biosynthesis remained unclear. In this study, the nectrisine biosynthetic gene cluster in T. discophora was identified from the contiguous genome sequence around the necC gene. Gene disruption and complementation studies and heterologous expression of the gene showed that necA, necB, and necC could be involved in nectrisine biosynthesis, during which amination, dephosphorylation, and oxidation occur. It was also demonstrated that nectrisine could be produced by recombinant Escherichia coli coexpressing the necA, necB, and necC genes. These findings provide the foundation to develop a bacterial production system for nectrisine or its intermediates through genetic engineering.