DEMONSTRATION OF POSITIONALLY DISORDERED WATER WITHIN A PROTEIN HYDROPHOBIC CAVITY BY NMR

The presence and location of water of hydration (thai is, bound water) in the solution structure of human interleukin-1 beta (hIL-1 beta) wa s investigated with water-selective two-dimensional heteronuclear magn etic resonance spectroscopy. It is shown here that in addition to wate r al the surface of the protein and ordered internal water molecules i nvolved in bridging hydrogen bonds, positionally disordered water is p resent within a large, naturally occurring hydrophobic cavity located at the center oi the molecule. These water molecules of hydration have residency times in the range of 1 to 2 nanoseconds to 100 to 200 micr oseconds and can be readily detected by nuclear magnetic resonance (NM R). Thus, large hydrophobic cavities in proteins may not be truly empt y, as analysis oi crystal structures appears to show, but may contain mobile water molecules that are crystallographically invisible but det ectable by NMR.