Studies of Heme Enzyme PrnB in Pyrrolnitrin Biosynthesis

Pyrrolnitrin (PRN) is a bioactive halometabolite produced from L-tryptophan (L-Trp) through a four-enzyme biosynthetic pathway involving PrnA, PrnB, PrnC, and PrnD. PrnB catalyzes an oxidative ring rearrangement but remains mechanistically unresolved due to the failure to reconstitute activity in vitro. To address this, we examined two PrnB homologs (PsPrnB and FbPrnB) and characterized the binding conformation and affinities of PrnB with two substrates (7-Cl-Trp and Trp) and two substrate analogs (TAM and IDPA). UV-vis spectroscopy and cocrystal structures confirmed that all four ligands bind to PrnB, with the amino group directly coordinating to the heme iron center. Stopped-flow and HPLC analyses showed that PrnB can generate heme-based oxidants upon reaction with O2 or H2O2; however, these oxidants do not generate product in the absence of additional components, suggesting that PrnB requires redox systems for catalytic turnover. To identify the potential redox component, we have explored several redox systems. This seminar will present our structural and spectroscopic studies on PrnB, along with current progress toward understanding its redox interaction with the associated redox systems.

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