UC Berkeley

Through evolution, Nature has developed enzymes that perform challenging reactions. By exploring biosynthetic pathways in bacteria, we can discover and repurpose these enzymes for synthetic applications. Here, we have performed metabolomics and enzyme characterization to elucidate the biosynthesis of β-ethynylserine (βes), an alkyne-containing amino acid made by Streptomyces cattleya. In the process, we discovered a novel FeII/α-ketoglutarate (FeII/αKG)- dependent halogenase, BesD, with unprecedented reactivity toward amino acids. We solved the crystal structure of BesD, discovered homologs that enable the formation of nine new chlorinated amino acids, and demonstrated that the newly discovered enzymes also perform bromination and azidation. Next, we demonstrated that halogenated amino acids can be further transformed enzymatically into chlorinated heterocycles, diamines, keto-acids, and peptides. Finally, we investigated how halogenases achieve regioselectivity, substrate selectivity, and catalytic selectivity (halogenation over the closely related hydroxylation reaction). These radical amino acid halogenases set the stage for the discovery of novel natural products that are formed via halogenated intermediates.