Small molecules containing the N-nitroso group, such as the bacterial natural product streptozotocin, are prominent carcinogens1,2 and important cancer chemotherapeutics3,4. Despite the considerable importance of this functional group to human health, enzymes dedicated to the assembly of the N-nitroso unit have not been identified. Here we show that SznF, a metalloenzyme from the biosynthesis of streptozotocin, catalyses an oxidative rearrangement of the guanidine group of Nω-methyl-l-arginine to generate an N-nitrosourea product. Structural characterization and mutagenesis of SznF reveal two separate active sites that promote distinct steps in this transformation using different iron-containing metallocofactors. This biosynthetic reaction, which has little precedent in enzymology or organic synthesis, expands the catalytic capabilities of non-haem-iron-dependent enzymes to include N–N bond formation. We find that biosynthetic gene clusters that encode SznF homologues are widely distributed among bacteria—including environmental organisms, plant symbionts and human pathogens—which suggests an unexpectedly diverse and uncharacterized microbial reservoir of bioactive N-nitroso metabolites.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The nucleotide sequences for the szn biosynthetic gene cluster and individual genes have been deposited into the NCBI (GenBank accession number for the szn gene cluster: MK303572; Genbank accession numbers for SznA–SznL: MK291255–MK291266). Structural factors and coordinates of SznF have been deposited in the Protein Data Bank (PDB: 6M9R, 6M9S). Additional data that support the conclusions of the paper can be requested from the corresponding authors.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
We thank J. Wang for assistance with LC–MS method development and analysis, M. Wilson for assistance with chemical synthesis and NMR characterization, J. Bergman for assistance with crystallography experiments, and L. Rajakovich for assistance with crystallography data analysis and reading the manuscript. We thank J. M. Bollinger Jr. and C. Krebs for discussions of proposed mechanisms and W. Zhang for providing E. coli WM6026. We acknowledge support from the National Institutes of Health (DP2 GM105434 to E.P.B. and GM119707 to A.K.B.), a Cottrell Scholar Award (to E.P.B.), a Camille Dreyfus Teacher-Scholar Award (to E.P.B.), the Searle Scholars Program (to A.K.B.), and Harvard University. GM/CA@APS has been funded in whole or in part with Federal funds from the National Cancer Institute (ACB-12002) and the National Institute of General Medical Sciences (AGM-12006). This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The Eiger 16M detector was funded by an NIH–Office of Research Infrastructure Programs, High-End Instrumentation Grant (1S10OD012289-01A1). Use of the LS-CAT Sector 21 was supported by the Michigan Economic Development Corporation and the Michigan Technology Tri-Corridor (grant 085P1000817).