5 - Experimental Techniques and Data Banks

Abstract

The bulk of knowledge about three-dimensional (3D) structures of biological macromolecules comes from X-ray crystallographic investigations. Macromolecular X-ray crystallography is a later extension of classical X-ray crystallography. A brief outline is necessary for the nonspecialist who uses the coordinates determined from a crystallographic investigation to be able to judge the quality of the results and to understand the limitations of the method. The heart of any X-ray crystallographic experiment is always a crystal. Once the location of all atoms in the asymmetric unit has been determined, application of symmetry generates the full unit cell. Since the mid-1980s, techniques based on Nuclear Magnetic Resonance (NMR) spectroscopy have also allowed the full elucidation of 3D structures of biological macromolecules to atomic detail. Since NMR examines molecules in a solution instead of the crystalline state and it allows investigations into the dynamics of structure whereas the crystal structure is a much more static view, the two methods complement each other extremely well. The chapter presents a qualitative description of NMR phenomena. An NMR spectroscopy takes advantage of the fact that some nuclei have protons with unpaired spins. This spinning charge generates a magnetic field that will either align with (parallel to) or against (antiparallel to) an applied external magnetic field. Experimentally derived structures form the factual foundation on which the knowledge and understanding of biological macromolecular structures are built. Knowledge of the structures of the basic building blocks led to predictions about how polymers of these could arrange themselves in 3D.