The energy landscape of ATP binding to the allosteric ATP-binding site of the UMP kinase as a function of the progress of ATP binding.

<p>(A) The six snapshots of the allosteric ATP binding pathway represent the following configurations: A, the unbound state; B, the “encounter complex”; C, an intermediate state featuring unfavorable electrostatic repulsions between Arg117^A,B and adenine; D, the relatively high-energy state; E; an intermediate state featuring favorable electrostatic interactions between the UMP kinase and ATP; F, the fully bound state. The ATP and its interacting residues are shown as sticks, whereas subunits A and B of the UMP kinase are shown in pale cyan and light blue, respectively. The green dashes represent hydrogen bonds. The hydrogen atoms are not displayed for clarity. The error bars represent standard deviations of binding energies for the 20 snapshots from 20 trajectories.