NMR IDENTIFICATION OF HYDROPHOBIC CAVITIES WITH LOW WATER OCCUPANCIESIN PROTEIN STRUCTURES USING SMALL GAS MOLECULES

Magnetization transfer through dipole-dipole interactions (nuclear Ove rhauser effects, NOEs) between water protons and the protons lining tw o small hydrophobic cavities in hen egg-white lysozyme demonstrates th e presence of water molecules with occupancies of similar to 10-50 %. Similarly, NOEs were observed between the cavity protons and the proto ns of hydrogen, methane, ethylene or cyclopropane applied at 1-200 bar pressure. These gases can thus be used as general NMR indicators of e mpty or partially hydrated hydrophobic cavities in proteins. All gases reside in the cavities for longer than 1 ns in marked contrast to com mon belief that gas diffusion in proteins is not much slower than in w ater. Binding to otherwise empty cavities may be a major aspect of the anesthetic effect of small organic gas molecules.