Elucidation of Chalkophomycin Biosynthesis Reveals N -Hydroxypyrrole-Forming Enzymes.

Reactive functional groups, such as N -nitrosamines, impart unique bioactivities to the natural products in which they are found. Recent work has illuminated enzymatic N -nitrosation reactions in microbial natural product biosynthesis, motivating interest in discovering additional metabolites constructed using such reactivity. Here, we use a genome mining approach to identify over 400 cryptic biosynthetic gene clusters (BGCs) encoding homologues of the N -nitrosating biosynthetic enzyme SznF, including the BGC for chalkophomycin, a Cu II -binding metabolite that contains a C -type diazeniumdiolate and N -hydroxypyrrole. Characterizing chalkophomycin biosynthetic enzymes reveals previously unknown enzymes responsible for N -hydroxypyrrole biosynthesis, including the first prolyl- N -hydroxylase, and a key step in the assembly of the diazeniumdiolate-containing amino acid graminine. Discovery of this pathway enriches our understanding of the biosynthetic logic employed in constructing unusual heteroatom-heteroatom bond-containing functional groups, enabling future efforts in natural product discovery and biocatalysis.