Combining experimental information from crystal and solution studies: Joint x-ray and NMR refinement

Joint refinement of macromolecules against crystallographic and nuclear magnetic resonance (NMR) observations is presented as a way of combining experimental information from the two methods. The model of interleukin-1β derived by the joint x-ray and NMR refinement is shown to be consistent with the experimental observations of both methods and to have crystallographic R value and geometrical parameters that are of the same quality as or better than those of models obtained by conventional crystallographic studies. The few NMR observations that are violated by the model serve as an indicator for genuine differences between the crystal and solution structures. The joint x-ray-NMR refinement can resolve structural ambiguities encountered in studies of multidomain proteins, in which low- to medium-resolution diffraction data can be complemented by higher resolution NMR data obtained for the individual domains.