Highlighting Cavities in Proteins by NMR Using Sulfur Hexafluoride as a Spy Molecule.

Cavities in proteins can be studied exptl. by using some detectable atoms, such as xenon, or mols. which act as reporter, such as a spy. The interest of sulfur hexafluoride (SF6) for probing hydrophobic cavities by soln.-state NMR is investigated. The wheat nonspecific lipid transfer protein (LTP) was selected as a model system for this purpose. The binding of SF6 is straightforwardly detected by the 19F chem. shift, line width, or longitudinal relaxation time measurements, which can be carried out at low SF6 concn. without interference from resonances of the protein. Most interestingly, the binding of SF6 gives rise to selective intermol. 1H{19F} heteronuclear Overhauser effects (HOEs). Mol. dynamics simulation and NMR spectrum modeling show that the exptl. HOESY spectra are consistent with 1H{19F} HOEs arising from SF6 in the cavity of LTP. SF6 is an advantageous alternative to hyperpolarized 129Xe and small org. compds. for probing cavities in proteins by soln.-state NMR. [on SciFinder(R)]