Elucidation of the Biosynthesis of Pantocin A

Pantocin A is a ribosomally synthesized, post-translationally modified peptide (RiPP) natural product that exhibits antibiotic activity through the inhibition of histidine biosynthesis. The gene cluster that gives rise to pantocin A contains genes for two putative biosynthetic enzymes, PaaA and PaaB. PaaA has previously been shown to modify the EEN core of the precursor peptide to generate a bicyclic structure similar to, but distinct from, the final structure of pantocin A; no characterization of PaaB has been reported to date. Herein, we determine the structure of the PaaA product, resolving the outstanding ambiguity in previous structural characterization. Moreover, we show that this species is accepted as a substrate by PaaB, an Fe(II)- and 2-oxoglutarate-dependent enzyme that catalyzes a unique 1,4-dehydrogenation to furnish the mature post-translational modification. These studies complete the biosynthetic pathway of pantocin A and the steps involved in its maturation.