Nitrososynthase-Triggered Oxidative Carbon–Carbon Bond Cleavage in Baumycin Biosynthesis

Abstract

Baumycins are coproduced with clinically important anticancer secondary metabolites daunorubicin and doxorubicin, which are glycosylated anthracyclines isolated from Streptomyces peucetius. The distinguishing feature of baumycins is the presence of an unusual acetal moiety appended to daunosamine, which is hydrolyzed during acidic extraction of daunorubicin from fermentation broth. The structure of the baumycin acetal suggests that it is likely derived from an unknown C-3” methyl deoxysugar cleaved between the C-3” and C-4” positions. This is supported by analysis of the baumycin/daunorubicin biosynthetic gene cluster (dox), which also encodes putative proteins consistent with production of an anthracycline dissacharide containing a branched sugar. Notably, the dnmZ gene in the dox gene cluster possesses high translated sequence similarity to nitrososynthases, which are flavin-dependent amine monooxygenases involved in the four electron oxidation of aminosugars to nitrososugars. Herein we demonstrate that DnmZ is an amino sugar nitrososynthase initiating the conversion of thymidine-5’-diphosphate-l-epi-vancosamine to a ring opened product via a previously uncharacterized retro oxime-aldol reaction.

Heteroatom–Heteroatom Bond Formation in Natural Product Biosynthesis

“…Lastly, a related nitrososynthase, DnmZ (59% amino acid identity to ORF36), has been demonstrated in vitro to also catalyze the four electron oxidation of 123 to 124 in the biosynthesis of the baumycin family of anthracycline natural products. 338 …”

“…In the biosynthesis of baumycin, 124 undergoes a retro oxime-aldol reaction that results in C–C bond cleavage to generate an aldehyde–oxime intermediate instead of further oxidation to the nitrosugar. 338 This unstable intermediate has been characterized extensively by MS/MS. Methylation of 123 at the 4-OH to form TDP-L-evernosamine by RubN7 has been shown to prevent this oxidative cleavage, allowing further N -oxidation of the nitroso group by ORF36.…”

The Enzymology of Organic Transformations: A Survey of Name Reactions in Biological Systems

“…[19] The overall rearrangement is a retro oxime-aldol transformation and bears a resemblance to that by Type I aldolases. The polarized nitroso functional group in this case is the surrogate for the iminium group of an aldolase.…”

Cryptic indole hydroxylation by a non-canonical terpenoid cyclase parallels bacterial xenobiotic detoxification

“…78), and NcnH79 and the glycoside-modifying N -oxygenases KijD3 (ref. 53) and DnmZ80. Thus, it appears that various enzymes that catalyse secondary metabolite tailoring reactions could have evolved from detoxification pathways, yet this relationship has been overlooked.…”