Fig. 22. Fosfomycin binding to FosA from K. pneumoniae (PDB ID 5V3D). FosA key residues involved in the binding of fosfomycin include Lys93, Ser97, Ser101, Tyr103, and Arg122. The Mn²⁺ ion acts as a Lewis acid during the nucleophilic attack by glutathione. A K⁺ at the active site does not take part in the catalysis reaction but enhances the electrophilicity of the Mn²⁺ ion, increasing the rate of reaction.²²⁹.