Dipolar relaxation, membranes

Brown, M.E 1984. Theory of spin-lattice relaxation in hpid bUayers and biological membranes. Dipolar relaxation. J. Chem. Phys. 80 2808-2831. 

Keywords Dynamics, Solution NMR, Solid-state NMR, Globular proteins. Membrane proteins. Order parameters. Relaxation rates. Dipolar couplings. Dynamic interference... 

The issue of what causes line broadening in solid-state NMR was thoroughly investigated by Su et al To understand the linewidth contributions to membrane protein NMR spectra, T2 relaxation times of uniformly labeled residues which show that the homogeneous line widths are determined by conformation-independent factors, including residual dipolar coupling, J-coupling, and intrinsic T2 relaxation. Examples of this were shown by TAT and other peptides. 

The membrane-bound structure, lipid interaction, and dynamics of the arginine-rich p-hairpin antimicrobial peptide PG-1 has been studied by solid-state NMR. A variety of solid-state NMR techniques, including paramagnetic relaxation enhancement, and spin diffusion, dipolar recoupling distance experiments, and 2D anisotropic-isotropic correlation experiments, were used to elucidate the structural basis for the membrane disruptive activity of this representative p-hairpin antimicrobial peptide. 

Finally, structural investigations of a human calcitonin-derived carrier peptide in a membrane enviromnent by solid-state NMR have been reported. The typical axially symmetric powder patterns of NMR spectra were used to confirm the presence of lamellar bilayers in the samples studied. The chemical shift anisotropy of the NMR spectra was monitored in order to reveal weak interaction of the peptide with the lipid headgroups. In addition, paramagnetic enhancement of relaxation rates and NMR order parameters of the phospholipid fatty acid chains in the absence and presence of the carrier peptide were measured. All peptide signals were resolved and fully assigned in 2D proton-driven spin diffusion experiments. The isotropic chemical shifts of CO, C and provided information about the secondary structure of the carrier peptide. In addition, dipolar eoupling measurements indicated rather high amplitudes of motion of the peptide. 

---