Nuclear Magnetic Resonance and Molecular Structure Dynamics (R. H. Austin¹)

Abstract

In Part ref Part III we discussed in some detail the evidence for and importance of protein structural dynamics in light of a free-energy landscape. However, there is a major problem with the powerhouse technique of X-ray crystallography that we discussed in Chapter 25: The proteins are locked into a crystal structure. If many proteins really need to make large conformational changes for their biological function, then it is worrisome that the structures we obtain from X-ray crystallography are static and possibly not fully functional structures. While it is possible to obtain a fair amount of dynamic information about proteins from X-ray crystallography using the Debye-Waller factors, it still is by no means the whole picture. The analogy might be to a person tied down in a chair, with a gag in the mouth. The person can struggle to get out; by looking at the little wiggles of the body as the person struggles to get free (these are the Debye-Waller factors), you might get some idea of how that person moves when free, but you will have no idea if the person is a world-class sprinter or a world-class mountain climber, quite different motions! Until fairly recently, it was very difficult to obtain 3-D structures of biomolecules in their native habitat (that is, in a solvent) at high (0.1 nm) resolution. Now, we are beginning to do this, and much more: We are beginning to chart their motions. In this chapter we try to give the reader a brief introduction to this exciting development.