Malonate-bound structure of the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ) and characterization of the native Fe²⁺ metal-ion preference

The structure of a malonate-bound form of the glycerophosphodiesterase from Enterobacter aerogenes, GpdQ, has been refined at a resolution of 2.2 Å to a final R factor of 17.1%. The structure was originally solved to 2.9 Å resolution using SAD phases from Zn²⁺ metal ions introduced into the active site of the apoenzyme [Jackson et al. (2007), J. Mol. Biol. 367, 1047-1062]. However, the 2.9 Å resolution was insufficient to discern significant details of the architecture of the binuclear metal centre that constitutes the active site. Furthermore, kinetic analysis revealed that the enzyme lost a significant amount of activity in the presence of Zn²⁺, suggesting that it is unlikely to be a catalytically relevant metal ion. In this communication, a higher resolution structure of GpdQ is presented in which malonate is visibly coordinated in the active site and analysis of the native metal-ion preference is presented using atomic absorption spectroscopy and anomalous scattering. Catalytic implications of the structure and its Fe ²⁺ metal-ion preference are discussed.