Integrative Structural Biology: Using X-ray Crystallography, Small-Angle X-ray Scattering, and Cryogenic Electron Microscopy to Determine Protein Structures

The field of structural biology focuses on determining and studying the structures of macromolecules in order to understand how three-dimensional shape dictates function at the molecular level. There are a variety of experimental tools that can be used to determine protein structures, and each technique has its strengths and weaknesses. This chapter focuses on three of these techniques: X-ray crystallography, small-angle X-ray scattering (SAXS), and cryogenic electron microscopy (cryo-EM). Each technique is introduced, and its strengths and weaknesses as a tool for protein structure determination are discussed. The emphasis of this chapter is that while these techniques on their own can provide a wealth of information regarding protein structure, when combined they complement each other to paint a more complete picture of the three-dimensional architecture of proteins. Two examples from the literature are provided where all three techniques were utilized to learn the fine details of protein structure. The first example reveals the structural details of how multiple proteins assemble to replicate DNA, while the second shows how multiple structures of a single enzyme with and without substrate bound can provide the molecular details of a catalytic cycle