SOLUTION STRUCTURE STUDIES OF D(AC)4.D(GT)4 VIA RESTRAINED MOLECULAR-DYNAMICS SIMULATIONS WITH NMR CONSTRAINTS DERIVED FROM 2-DIMENSIONAL NOE AND DOUBLE-QUANTUM-FILTERED COSY EXPERIMENTS

The structure of d(AC)4.d(GT)4 is investigated by constrained molecular dynamics simulations. The constraints include proton pair distances derived from 2D NOE intensities by using the iterative relaxation matrix analysis algorithm MARDIGRAS and sugar pucker phases and amplitudes derived from double-quantum-filtered COSY spectra. Molecular dynamics runs on simulated intensity and distance sets as well as the experimental data were carried out to determine the effects of starting structure, distance constraints derivation, energy functions, and experimental errors on the end result. It was found that structural details could not be elucidated within about 1.5-angstrom overall atomic deviation. This limitation is due in part to the accuracy of the experimental data but, more importantly, is attributable to the quantity of experimental constraints available and to imperfections in the force field utilized in the molecular dynamics calculations. Within the limits of the method, some structural characteristics of d(AC)4.d(GT)4 could be elucidated.