Influence of non-bonded parameters on the quality of NMR structures: A newforce field for NMR structure calculation

The effects of different non-bonded parameters of force fields for NMR stru cture calculation on the quality of the resulting NMR solution structures w ere investigated using Interleukin 4 as a model system. NMR structure ensem bles were calculated with an ab initio protocol using torsion angle dynamic s. The calculations were repeated with five different non-bonded energy fun ctions and parameters. The resulting ensembles were compared with the avail able X-ray structures, and their quality was assessed with common structure validation programs. In addition, the impact of torsion angle restraints a nd dihedral energy terms for the sidechains and the backbone was studied. T he further improvement of the quality by refinement in explicit solvent was demonstrated. The optimal parameters, including those necessary for water refinement, are available in the new version of the PARALLHDG force field.