Protein–Protein Interactions in the Solid State: The Troubles of Crystallizing Protein–Protein Complexes

The determination of the tri-dimensional structure of protein-protein interfaces is an important step for every research program aimed to the discovery of molecules able to interfere with protein-protein interactions. The main issue regarding the structure determination by X-ray crystallography of protein-protein interfaces and of the interactions with molecules able to interfere or regulate such interactions, deals with the ability to obtain such complexes in the crystalline state. This chapter deals with the experimental problems related to obtaining pure proteins and protein complexes and their crystallization strategies. Selected examples from the literature are provided.