Fosfomycin resistance protein (FosA) is a manganese metalloglutathione transferase related to glyoxalase I and the extradiol dioxygenases

The enzyme conferring resistance to the antibiotic fosfomycin [(1R,2S)-1,2-epoxypropylphosphonic acid] originally reported by Suarez and co-workers [Area, P., Hardisson, C., & Suarez, J. E. (1990) Antimicrob. Agents Chemother. 34, 844-848] is demonstrated in this study to be a metalloglutathione transferase. The apoenzyme is a dimer of 16 kDa subunits. Electron paramagnetic resonance spectroscopy and water proton nuclear magnetic resonance longitudinal relaxation rates suggest that each subunit contains a mononuclear Mn2+ center that interacts strongly with the substrate fosfomycin (K-d = 17 mu M) more weakly with the product (K-d = 1.1 mM) and very weakly or not at all with GSH. Inhomogeneous broadening of the EPR signals of enzyme-bound Mn2+ in the presence of (H2O)-O-17 indicates that three of the coordination sites on the metal are occupied by water. Sequence alignments, three-dimensional structures, and mechanistic considerations suggest that FosA is related to at least two other metalloenzymes, glyoxalase I and the Mn2+- or Fe2+-containing extradiol dioxygenases. The mechanistic imperative driving the evolution of this, previously unidentified superfamily of metalloenzymes is proposed to be bidentate coordination of a substrate or intermediate to the metal center in the enzyme-catalyzed reactions.