Experimental Methods of Structure Determination

Abstract

In this chapter we want to turn to the experimental structure determination methods of ligands and proteins. There are two techniques in particular that deliver information about the three-dimensional structure of small organic molecules all the way to proteins: crystal structure analysis and high-resolution NMR spectroscopy. The first technique is the older method. It goes back to an experiment of Max von Laue in 1912. It was just 17 years earlier that Wilhelm Röntgen had discovered an electromagnetic radiation, which was later named X-rays or “Roentgen rays” in German in honor of him. Together with his collaborators Walter Friedrich and Paul Knipping, Laue was able to demonstrate the wave nature of X-rays with a copper sulfate crystal. At the same time they proved the lattice structure of crystals. Only one year later William Lawrence Bragg and his father William Henry Bragg reaped the rewards of these experiments. They determined the crystal structure of sodium chloride. The technique has grown over the years. Today the structures of proteins with 4,000 amino acids have been determined. In the last years electron microscopy has proven to be a very powerful crystal diffraction technique tool for the structure elucidation of membrane-bound proteins and viruses. NMR spectroscopy is likewise a relatively young technique. In 1945 the research group of Felix Bloch and Edward Purcell in the USA observed the resonance stimulation of hydrogen atom nuclei in a magnetic field for the first time. From this experiment the technique has grown, mostly due to progress with the apparatus, to the extent that the structure determination of proteins with more than 800 amino acids has been accomplished. For this, however, the protein must be extensively labeled with different isotopes.