FIG. 1.

Overview of the binding site inside the catalytic center, which is revealed by the crystal structure of the PA_N complex with rUMP. (A) Overall view of the PA_N and rUMP complex. The rUMP binding site inside the catalytic center is represented by electron density and shown as blue mesh, while the bound Mg²⁺ and coordinated solvent molecules are covered by red mesh. Secondary structure elements of the PA_N polypeptide are colored light pink (helices) and green (strands). (B) Electrostatic surface potential of the rUMP binding site. PA_N is shown covered by an electrostatic surface, colored blue for positive charge and red for negative charge, while bound rUMP is shown as yellow sticks. The Mg²⁺ ions and solvent molecules are shown as spheres, and relevant secondary structure elements are labeled. The location of the second metal ion (corresponding to the Mn²⁺-bound structure) is indicated by a black arrow and small gray sphere.