Triplex hydration: nanosecond molecular dynamics simulation of the solvated triplex formed by mixed sequences.

A theoretical model for the hydration pattern and motion of ions around the triple helical DNA with mixed sequences d(GACTGGTGAC)d(GTCACCAGTC)*d(GACTGGTGAC) in solution, during MD simulation, using the particle mesh Ewald sum method, is elaborated here. The AMBER 5.0 force field has been used during the simulation in solvent. The simulation studies support a dynamically stable atmosphere around the DNA triplex in solution over the entire length of the trajectory. The results have been compared with Hoogsteen triplexes and examined in the context of the observed behaviour of hydration in crystallographic data of duplexes. The dynamical organization of counterions and water molecules around the triplex formed by mixed sequences is described here. It has been observed that cations prefer to bind between two adjoining purines of the second and the third strands. The idea of localized complexes (mobile counterions in unspecific electronegative pockets around the DNA triplex with water molecules) may have important implications for understanding the specificity of the interactions of nucleic acids with proteins and other ligands.