Two 3′-<i>O</i>-β-glucosylated nucleoside fluorometabolites related to nucleocidin in <i>Streptomyces calvus</i>

Abstract

The antibiotic nucleocidin is a product of the soil bacterium <i>Streptomyces calvus</i> T-3018. It is among the very rare fluorine containing natural products but is distinct from the other fluorometabolites in that it is not biosynthesised from 5'-fluorodeoxyadenosine <i>via</i> the fluorinase. It seems to have a unique enzymatic fluorination process. We disclose here the structures of two 4'-fluoro-3'-<i>O</i>-β-glucosylated metabolites (F-Mets I and II) which appear and then disappear before nucleocidin production in batch cultures of <i>S. calvus</i>. Full genome sequencing of <i>S. calvus</i> T-3018 and an analysis of the putative biosynthetic gene cluster for nucleocidin identified UDP-glucose dependent glucosyl transferase (<i>nucGT</i>) and glucosidase (n<i>ucGS</i>) genes within the cluster. We demonstrate that these genes express enzymes that have the capacity to attach and remove glucose from the 3'-<i>O</i>-position of adenosine analogues. In the case of F-Met II, deglucosylation with the NucGS glucosidase generates nucleocidin suggesting a role in its biosynthesis. Gene knockouts of <i>nucGT</i> abolished nucelocidin production.