Structural Basis of Regiospecificity of a Mononuclear Iron Enzyme in Antibiotic Fosfomycin Biosynthesis

Hydroxypropylphosphonic acid epoxidase (HppE) is an unusual mononuclear iron enzyme that uses dioxygen to catalyze the oxidative epoxidation of (S)-2-hydroxypropylphosphonic acid (S-HPP) in the biosynthesis of the antibiotic fosfomycin. Additionally, the enzyme converts the R-enantiomer of the substrate (R-HPP) to 2-oxo-propylphosphonic acid. To probe the mechanism of HppE regiospecificity, we determined three X-ray structures: R-HPP with inert cobalt-containing enzyme (Co(II)–HppE) at 2.1 Å [angstrom] resolution; R-HPP with active iron-containing enzyme (Fe(II)–HppE) at 3.0 Å [angstrom] resolution; and S-HPP–Fe(II)–HppE in complex with dioxygen mimic NO at 2.9 Å [angstrom] resolution. These structures, along with previously determined structures of S-HPP–HppE, identify the dioxygen binding site on iron and elegantly illustrate how HppE is able to recognize both substrate enantiomers to catalyze two completely distinct reactions.National Institutes of Health (U.S.) (Grant GM40541)National Institutes of Health (U.S.) (Grant F32 GM079966)National Institutes of Health (U.S.) (Center Grant P30 ES002109)Howard Hughes Medical Institut