Nuclear Magnetic Resonance and Molecular Structure Dynamics (R. H. Austin1)
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.
KeywordsDensity Matrix Rabi Frequency Free Induction Decay Magnetic Dipole Moment Pickup Coil
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