ABSTRACT
X-ray crystallography is based on diffraction of x-rays in an ordered material. The protein sample has to be prepared as a single crystal, where the molecules are ordered in unit cells. Each unit cell may contain one or more molecules in an ordered arrangement, and then the unit cells have to be packed so that all have the same orientation
10.1 Making Crystals .......................................................................................... 159 10.2 X-Ray Sources ............................................................................................ 160 10.3 The Diffraction Experiment ........................................................................ 161 10.4 The Phase Problem...................................................................................... 162 10.5 Building the Structure Model ...................................................................... 164 10.6 Rening the Structure ................................................................................. 164 10.7 Protein Data Banks ..................................................................................... 164 10.8 Membrane Proteins ..................................................................................... 165
relative to the macroscopic dimensions of the crystal. Since protein molecules typically have irregular shapes, they are surrounded by disordered solvent molecules and make only a few direct molecular contacts among themselves. Making welldiffracting single crystals is a bottleneck in x-ray crystallography. Many procedures have been developed for crystallization, and conditions have to be varied over many parameters and wide ranges in order to produce well-behaving crystals that can be used for investigations.
