Chloramphenicol is synthesized by Streptomyces venezuelae from L-para-aminophenylalanine (PAPA) using a nonribosomal peptide synthetase (NRPS, CmlP) and associated tailoring enzymes. Two of the latter enzymes employ nonheme dinuclear iron clusters to activate O2 for incorporation of oxygen atoms into the developing antibiotic. CmlA, a β-hydroxylase, and CmlI, an amine oxygenase, are archetypal enzymes for the application of the dinuclear iron cofactor in NRPS-mediated biosynthetic pathways. Ongoing studies suggest that CmlA transfers oxygen to the substrate from a high valent state of the diiron cluster while CmlI employs a diiron(III)-peroxo intermediate to carry out the 6 electron oxidation of an aromatic amine precursor to the aryl-nitro moiety of the active antibiotic. Resonance Raman and XAS spectroscopies suggest that the CmlI-peroxo intermediate has a unique geometry in comparison to other characterized enzymatic peroxo species. Here, crystallographic, kinetic, and spectroscopic studies are combined to provide insight into how the similar diiron clusters of CmlA and CmlI are directed to stabilize different reactive intermediates, and then carry out very distinct chemical reactions.

Diiron enzymes in antibiotic biosynthesis: Similar metal centers - different chemistry

253rd National Meeting (2017)

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