Restrained molecular dynamics of solvated duplex DNA using the particle mesh Ewald method

Restrained and unrestrained aqueous solution molecular dynamics simulations applying the particle mesh Ewald (PME) method to DNA duplex structures previously determined via in vacuo restrained molecular dynamics with NMR-derived restraints are reported. Without experimental restraints, the DNA decamer, d(CATTTGCATC).d(GATGCAAATG) and trisdecamer, d(AGCTTGCCTTGAG).d(CTCAAGGCAAGCT), structures are stable on the nanosecond time scale and adopt conformations in the B-DNA family. These free DNA simulations exhibit behavior characteristic of PME simulations previously performed on DNA sequences, including a low helical twist, frequent sugar pucker transitions, BI-BII(epsilon-zeta) transitions and coupled crakshaft (alpha-gamma) motion. Refinement protocols similar to the original in vacuo restrained molecular dynamics (RMD) refinements but in aqueous solution using the Cornell et al. force field [Cornell et al. (1995) J. Am. Chem. Soc., 117, 5179-5197] and a particle mesh Ewald treatment produce structures which fit the restraints very well and are very similar to the original in vacuo NMR structure, except for a significant difference in the average helical twist. Figures of merit for the average structure found in the RMD PME decamer simulations in solution are equivalent to the original in vacuo NMR structure while the figures of merit for the free MD simulations are significantly higher. The free MD simulations with the PME method, however, lead to some sequence-dependent structural features in common with the NMR structures, unlike free MD calculations with earlier force fields and protocols. There is some suggestion that the improved handling of electrostatics by PME improves long-range structural aspects which are not well defined by the short-range nature of NMR restraints.