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The three-dimensional structure of synthetic human neuropeptide Y in aqueous
solution at pH 3.2 and 37 degrees C was determined from two-dimensional 1H NMR
data recorded at 600 MHz. A restraint set consisting of 440 interproton distance
restraints inferred from NOEs and 11 backbone and 4 side-chain dihedral angle
restraints derived from spin-spin coupling constants was used as input for
distance geometry calculations on DIANA and simulated annealing and restrained
energy minimization in X-PLOR. The final set of 26 structures is well defined in
the region of residues 11-36, with a mean pairwise rmsd of 0.51 A for the
backbone heavy atoms (N, C alpha and C) and 1.34 A for all heavy atoms. Residues
13-36 form an amphipathic alpha-helix. The N-terminal 10 residues are poorly
defined relative to the helical region, although some elements of local
structure are apparent. At least one of the three prolines in the N-terminal
region co-exists in both cis and trans conformations. An additional set of 24
distances was interpreted as intermolecular distances within a dimer. A
combination of distance geometry and restrained simulated annealing yielded a
model of the dimer having antiparallel packing of two helical units, whose
hydrophobic faces form a well-defined core. Sedimentation equilibrium
experiments confirm the observation that neuropeptide Y associates to form
dimers and higher aggregates under the conditions of the NMR experiments. Our
results therefore support the structural features reported for porcine
neuropeptide Y [Cowley, D.J. et al. (1992) Eur. J. Biochem., 205, 1099-1106]
rather than the 'aPP' fold described previously for human neuropeptide Y
[Darbon, H. et al. (1992) Eur. J. Biochem., 209, 765-771].
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