DOI 10.1007/s00249-003-0339-2 ARTICLE

The conformational equilibria of MgATP in solution is studied using molecular dynamics (MD) augmented with umbrella sampling methods. Free energy comparisons show that the Mg ion is equally likely to coordinate the oxygens of the two end phosphates, or of all three phosphates. The MD trajectories reveal two major degrees of freedom of the MgATP molecule in solution, and we compute the free energy as a function of these variables, and determine its elastic properties. Comparing the free energy function with several crystallographic structures of ATP analogs, we find that the crystal structures correspond to states where ATP would be elastically strained. The average water density around MgATP is investigated to show the average number of hydrogen bonds and the hydrophobicity