Microsecond simulations of mdm2 and its complex with p53 yield insight into force field accuracy and conformational dynamics

The p53-MDM2 complex is both a major target for cancer drug development and a valuable model system for computational predictions of protein-ligand binding. To investigate the accuracy of molecular simulations of MDM2 and its complex with p53, we performed a number of long (200 ns to 1 mu s) explicit-solvent simulations using a range of force fields. We systematically compared nine popular force fields (AMBER ff03, ff12sb, ff14sb, ff99sb, ff99sb-ildn, ff99sb-ildn-nmr, ff99sb-ildn-phi, CHARMM22*, and CHARMM36) against experimental chemical shift data, and found similarly accurate results, with microsecond simulations achieving better agreement compared to 200-ns trajectories. Although the experimentally determined apo structure has a closed binding cleft, simulations in all force fields suggest the apo state of MDM2 is highly flexible, and able to sample holo-like conformations, consistent with a conformational selection model. Initial structuring of the MDM2 lid region, known to competitively bind the binding cleft, is also observed in long simulations. Taken together, these results show molecular simulations can accurately sample conformations relevant for ligand binding. We expect this study to inform future computational work on folding and binding of MDM2 ligands. Proteins 2015; 83:1665-1676. (c) 2015 Wiley Periodicals, Inc.