화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.126, No.48, 15738-15746, 2004
Probing the hydrophobic cavity of Lipid Transfer Protein from Nicotiana tabacum through xenon-based NMR spectroscopy
The hydrophobic cavity of Lipid Transfer Protein 1 from Nicotiana tabacum is investigated in detail by NMR using xenon as a spy. The analysis of the Xe-129 chemical shifts and self-relaxation times gives evidence of protein-xenon interaction. Thermodynamics of the binding is characterized through the study of aliphatic H-1 and C-13 chemical shift variation as a function of xenon pressure. The binding constant is evaluated to 75.5 +/- 1.0 M-1 at 293 K. The location of xenon inside the cavity is deduced from SPINOE experiments. The noble gas appears to occupy four sites, and xenon self-relaxation experiments indicate that it quickly jumps between different sites. The chemical shifts of amide protons and nitrogens also depend on the xenon concentration, either specifically or nonspecifically for atoms at the external surface of the protein. Yet, contrary to aliphatic atoms, they do not correspond to short-range interactions as confirmed by magnetization transfer experiments between laser-polarized xenon and protons in H2O. These N-15 chemical shift variations, used in combination with N-15 transverse self-relaxation rates to determine the lower limit of the binding rate, consequently reveal subtle changes in the structure of the protein upon binding.