Evidence that the fosfomycin-producing epoxidase, HppE, is a non-heme-iron peroxidase

The iron-dependent epoxidase HppE converts (S)-2-hydroxypropyl-1- phosphonate (S-HPP) to the antibiotic fosfomycin [(1R,2S)- epoxypropylphosphonate] in an unusual 1,3-dehydrogenation of a secondary alcohol to an epoxide. HppE has been classified as an oxidase, with proposed mechanisms differing primarily in the identity of the O2-derived iron complex that abstracts hydrogen (H•) from C1 of S-HPP to initiate epoxide ring closure. We show here that the preferred cosubstrate is actually H₂O ₂ and that HppE therefore almost certainly uses an iron(IV)-oxo complex as the H• abstractor. Reaction with H₂O₂ is accelerated by bound substrate and produces fosfomycin catalytically with a stoichiometry of unity. The ability of catalase to suppress the HppE activity previously attributed to its direct utilization of O₂ implies that reduction of O₂ and utilization of the resultant H₂O ₂ were actually operant.