Water: now you see it, now you don't.

Recent studies of water in and around proteins have made us acutely aware of the critical role that water plays in protein structure and function. They have also highlighted how little we know about the detailed behavior of water molecules. Four general questions can be asked about water molecules interacting with proteins. Where are they? How long do they stay there? How strongly do they interact with the protein? How do they affect protein structure and stability? Although we do not yet have definitive answers, a consensus is emerging, which brings together the three key techniques of modern structural research: crystallography, NMR spectroscopy, and computer methods of analysis and simulation. To reconcile the data produced by these different approaches, it is also necessary to keep clearly in mind what each technique actually measures (or calculates).