title: Structure and reactivity of hydroxypropylphosphonic acid epoxidase in fosfomycin biosynthesis by a cation- and flavin-dependent mechanism.
abstract: The biosynthesis of fosfomycin, an oxirane antibiotic in clinical use, involves a unique epoxidation catalyzed by (S)-2-hydroxypropylphosphonic acid epoxidase (HPPE). The reaction is essentially dehydrogenation of a secondary alcohol. A high-resolution crystallographic analysis reveals that the HPPE subunit displays a two-domain combination. The C-terminal or catalytic domain has the cupin fold that binds a divalent cation, whereas the N-terminal domain carries a helix-turn-helix motif with putative DNA-binding helices positioned 34 A apart. The structure of HPPE serves as a model for numerous proteins, of ill-defined function, predicted to be transcription factors but carrying a cupin domain at the C terminus. Structure-reactivity analyses reveal conformational changes near the catalytic center driven by the presence or absence of ligand, that HPPE is a Zn(2+)/Fe(2+)-dependent epoxidase, proof that flavin mononucleotide is required for catalysis, and allow us to propose a simple mechanism that is compatible with previous experimental data. The participation of the redox inert Zn(2+) in the mechanism is surprising and indicates that Lewis acid properties of the metal ions are sufficient to polarize the substrate and, aided by flavin mononucleotide reduction, facilitate the epoxidation.
authors.affiliation: Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.
authors.forename: Karen
authors.initials: K
authors.lastname: McLuskey
authors.forename: Scott
authors.initials: S
authors.lastname: Cameron
authors.forename: Friedrich
authors.initials: F
authors.lastname: Hammerschmidt
authors.forename: William N
authors.initials: WN
authors.lastname: Hunter
mesh_terms: D002151:Calorimetry; D002413:Cations, Divalent / Q000378:metabolism; D003461:Crystallography; D005415:Flavins / Q000378:metabolism; D005578:Fosfomycin / Q000096:biosynthesis*; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D013054:Spectrophotometry, Atomic; D013302:Streptomyces / Q000201:enzymology*
chemical_list: D002413:Cations, Divalent; D005415:Flavins; D005578:Fosfomycin; D010088:Oxidoreductases; C405402:2-hydroxypropylphosphonic acid epoxidase