The active site electron density observed in the MMNAT-POP complex.

<p>The crystal structure of MMNAT after reaction with compound <b>1</b> showed excess electron density connected to Cys70, into which a 3-phenyl-3-oxopropyl (POP) modification was modelled with full occupancy. All three cysteine residues in the MMNAT structure and the covalent modification (in pink) are shown with the electron density shown using blue 2Fo–Fc electron density contoured at 1 σ. This observation is compatible with the MS data, since the excess inhibitor was washed out prior to crystallisation and the native state of the protein was preserved throughout the structure determination process. The figures were prepared using PyMOL <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052790#pone.0052790-Schrodinger1" target="_blank">[67]</a>.