MECHANISTIC STUDIES OF AN UNUSUAL C-O BOND FORMATION IN FOSFOMYCIN BIOSYNTHESIS

The O₂-activating, non-heme iron enzymes catalyze a wide range of oxidation reactions with important biological implications, such as DNA repair, hypoxic response, collagen biosynthesis, and histone demethylation. Most of these enzymes possess a single iron center coordinated by two His and one Asp/Glu residues in a tridentate binding motif referred to as the "2-His-1-carboxylate facial triad". Understanding the mechanism of O₂-activation by these enzymes may provide key insights into the source of their diverse substrate specificities despite similarly coordinated active site metal centers. HppE is a unique member of this class of enzymes and functions as an iron-dependent epoxidase to convert (S)-2-hydroxypropyl-1-phosphonate (S-HPP) to the antibiotic fosfomycin. The reaction catalyzed by HppE is unusual, because it involves the 1,3-dehydrogenation of a secondary alcohol to an epoxide. Several mechanisms have been proposed for HppE catalysis, and these are differentiated primarily in terms of the identity of the O₂-activated iron complex that abstracts a hydrogen atom from C1 of S-HPP to initiate epoxide ring closure. Our recent results have shown that the preferred cosubstrate is H₂O₂ and that HppE uses an iron(IV)-oxo complex as the hydrogen atom abstractor. These results along with recent studies using radical probes to gain insight into the mechanism of this enzyme will be presented.