The NMR spectroscopy has been utilized widely for a elucidation of the structural change of a protein caused by the change of pH, ionic strength, temperature, and ligand concentration in solution. The X-ray was less utilized for these study excutable easily in solution, but is utilized much for the structural determination of a protein. Such difference has ever lead to the situation that the NMR relied on the structure solved by X-ray and the X-ray argued its struture in reference to the conformational change elucidated by NMR. However, recent developments of NMR spectroscopy made it possible to determine the three-dimensional structure, and the X-ray techniques has also been developped to clarify the structural change of a protein. This review compares the recent development of these two techniques, and will discuss about the future collaborating interaction between NMR and X-ray.
