Abstract
Phosphonate natural products have a history of successful application in medicine and biotechnology due to their ability to inhibit essential cellular pathways. This has inspired efforts to discover phosphonate natural products by prioritizing microbial strains whose genomes encode uncharacterized biosynthetic gene clusters (BGCs). Thus, success in genome mining is dependent on establishing the fundamental principles underlying the biosynthesis of inhibitory chemical moieties to facilitate accurate prediction of BGCs and the bioactivities of their products. Here, we report the complete biosynthetic pathway for the argolaphos phosphonopeptides. We uncovered the biochemical origins of aminomethylphosphonate (AMPn) and N(ε)-hydroxyarginine, two noncanonical amino acids integral to the antimicrobial function of argolaphos. Critical to this pathway were dehydrogenase and transaminase enzymes dedicated to the conversion of hydroxymethylphosphonate to AMPn. The interconnected activities of both enzymes provided a solution to overcome unfavorable energetics, empower cofactor regeneration, and mediate intermediate toxicity during these transformations. Sequential ligation of l-arginine and l-valine was afforded by two GCN5-related N-acetyltransferases in a tRNA-dependent manner. AglA was revealed to be an unusual heme-dependent monooxygenase that hydroxylated the N(ε) position of AMPn-Arg. As the first biochemically characterized member of the YqcI/YcgG protein family, AglA enlightens the potential functions of this elusive group, which remains biochemically distinct from the well-established P450 monooxygenases. The widespread distribution of AMPn and YqcI/YcgG genes among actinobacterial genomes suggests their involvement in diverse metabolic pathways and cellular functions. Our findings illuminate new paradigms in natural product biosynthesis and realize a significant trove of AmPn and N(ε)-hydroxyarginine natural products that await discovery.