Structural insight into antibiotic fosfomycin biosynthesis by a mononuclear iron enzyme

The biosynthetic pathway of the clinically important antibiotic fosfomycin uses enzymes that catalyse reactions without precedent in biology. Among these is hydroxypropylphosphonic acid epoxidase, which represents a new subfamily of non-haem mononuclear iron enzymes. Here we present six X-ray structures of this enzyme: the apoenzyme at 2.0 angstrom resolution; a native Fe(II)-bound form at 2.4 angstrom resolution; a tris( hydroxymethyl) aminomethane - Co( II)- enzyme complex structure at 1.8 angstrom resolution; a substrate - Co( II)- enzyme complex structure at 2.5 angstrom resolution; and two substrate - Fe( II)enzyme complexes at 2.1 and 2.3 angstrom resolution. These structural data lead us to suggest how this enzyme is able to recognize and respond to its substrate with a conformational change that protects the radical-based intermediates formed during catalysis. Comparisons with other family members suggest why substrate binding is able to prime iron for dioxygen binding in the absence of alpha-ketoglutarate ( a co-substrate required by many mononuclear iron enzymes), and how the unique epoxidation reaction of hydroxypropylphosphonic acid epoxidase may occur.