Messages from ultrahigh resolution crystal structures

The ever growing availability of macromolecular crystal structures determin ed at atomic resolution has now reached a critical size, making it possible to obtain statistically unbiased data on both protein stereochemistry and the validity of the parameters used in their refinement. Besides the determ ination of the precise geometry of proteins and their active sites, high re solution structures have made it possible to check the application of norma l mode calculations, to calculate charge density distributions and to analy ze hydration shells around protein molecules. Even if only a few structures involve protein complexes, either with ligands or prosthetic groups, the i nformation obtained in these cases is of great interest for obtaining the p hysical parameters of these interactions.