Why do g_mmpbsa and GMXPBSA2.1 only need the complex trajectory to calculate the binding energy?

Dear all,

As I understand, MM/PBSA method needs three MD trajectories to calculate the binding energy: (1) the complex trajectory; (2) the receptor trajectory; (3) the ligand trajectory. You calculate each energy entity (vdw, electrostatic, etc) for each of the three species (the complex, the receptor and the ligand) from their corresponding trajecotories and obtain the total energy for the three species (G[complex], G[protein], G[ligand]), and then calculate the binding energy with the following formula:
ΔG[binding] = G[complex] − (G[protein] + G[ligand])

However, both g_mmpbsa and GMXPBSA2.1 seem to use only the complex trajectory to calculate all the energy entities for all the three species. Wouldn’t that be wrong?

Best regards

Hi Jason,

indeed, this an approximation that is used in the tool. As the authors of g_mmbpsa mention in the publication related to the implementation:

Note, in the single trajectory approach, the conformation of protein and ligand in the bound and unbound forms are assumed to be identical

To be found here: