But when you can get it, structure can be a wonderful thing. X-ray crystallography of proteins, and protein-ligand complexes has revealed so much useful information that it's hard to know where to start. It's not the magic wand - you can't look at an empty binding site and just design something right at your desk that'll be a potent ligand right off the bat. And you can't look at a series of ligand-bound structures and say which one is the most potent, not in most situations, anyway. But you still learn things from X-ray structures that you could never have known otherwise.
It's not the only game in town, either. NMR structures are very useful, although the X-ray ones can be easier to get, especially in these days of automated synchroton beamlines and powerful number-crunching. But what if your protein doesn't crystallize? And what if there are things happening in solution that you'd never pick up on from the crystallized form? You're not going to watch your protein rearrange into a new ligand-bound conformation with X-ray crystallography, that's for sure. No, even though NMR structures can be a pain to get, and have to be carefully interpreted, they'll also show you things you'd never had seen.
