Solution structure by 1H and dynamics by natural abundance 13C NMR of a receptor recognising peptide derived from a C-terminal fragment of neuropeptide Y.

A peptide consisting of 20 amino acid residues, derived from a C-terminal fragment of neuropeptide Y (NPY) and showing high affinity to NPY receptors, was synthesised. Its sequence is PAADLARYRHYINLITRQRY-NH2, and the solution structure was calculated from NMR-derived distance and torsion angle restraints, obtained at 15 degrees C in a solvent mixture of water and 30% (v/v) 1,1,1,3,3,3-hexafluoro-2-propanol, by using DIANA and restrained energy minimisation. The structure was found to consist of a well-defined alpha-helix in the centre, with a few residues at the termini having less well defined conformations. The spin-lattice and spin-spin relaxation rates of alpha-carbons have been determined on 13C at natural abundance. From 1D experiments the global rotational correlation time was determined and from 2D experiments the dynamics of each individual residue was obtained. The results demonstrate that the C alpha-H alpha vectors in the alpha-helix essentially follow the global motion. Towards the termini, contributions from local dynamics increase. This tendency is correlated to the increasing uncertainty of the structure towards the peptide ends. An effective molecular volume was calculated from the temperature dependence of the global rotational correlation time. This is well compatible with a monomeric peptide, solvated by water and 1,1,1,3,3,3-hexafluoro-2-propanol. The presence of peptide dimers was ruled out as being inconsistent with the relaxation data.