Stabilized structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog N-acetyl[Leu-28,Leu-31]NPY(24-36)

Stabilization of the helical structure of Y2-selective analogues of neuropeptide Y by lactam bridges

The importance of helical structure in an analogue of NPY selective for the Y2 receptor, Ac[Leu28,31]NPY24-36, has been investigated by introducing a lactam bridge between positions 28 and 32. The resulting analogue, Ac-cyclo28/32[Ala24,Lys28,Leu31,Glu32]NPY24-36, is a potent Y2-selective agonist. Structural analysis by NMR shows that this analogue forms a helical structure in a 40% trifluoroethanol/water mixture, whereas in water only the region around the lactam bridge (Lys28-Glu32) adopts helical-like structure, with both N- and C-termini being poorly defined. The observation of well-defined helical structure in aqueous TFE contrasts with that reported for a similar analogue, Ac-cyclo28/32[Lys28,Glu32]NPY25-36 (Rist et al. FEBS Lett. 1996, 394, 169-173), which consisted of a hairpin-like structure that brought the N- and C-termini into proximity. We have therefore determined the structures of this analogue, as well as those of Ac-cyclo28/32[Ala24,Lys28,Leu31,Glu32]NPY24-36 and Ac-cyclo28/32[Ala24,Lys28,Glu32]NPY24-36, under identical solution conditions (30% TFE/H2O mixture at 308 K) and find essentially the same helical structure in all three peptides. These findings support the proposal that these Y2-selective analogues adopt a helical structure when bound to the Y2 receptor.

Structure-activity analysis of N-acetyl [Leu(28,31)] NPY 24-36: a potent neuropeptide Y Y(2) receptor agonist

Neuropeptide Y (NPY) and a C-terminal analog of NPY, N acetyl [Leu(28,31)] NPY 24-36, act at NPY Y(2) receptors to potently inhibit cardiac vagal activity. The C-terminal analog is equipotent as NPY in inhibiting cardiac vagal activity but does not retain any pressor or Y(1) activity. This study investigates the importance of each amino acid in the 13 residue analog for functional activity by systematically substituting each residue with L-alanine. The inhibitory effect on cardiac vagal action decreased with substitution at residues 25,26,28,29 and 31. No decrease in activity was observed with alanine substitution at residues 24, 27 or 30. Residues 32 and 34 retained activity only at high doses, while residues 33, 35 and 36 were not active following alanine substitution. The difference in potency of the effective analogs suggests secondary structure of the peptide is as important for activity as retaining key amino acids.

Helical structure and self-association in a 13 residue neuropeptide Y Y2 receptor agonist: relationship to biological activity

The solution structure and self-association behaviour of a 13 residue peptide analogue of the C-terminal region of human neuropeptide Y (NPY) have been investigated. NMR analysis of Ac[Leu(28,31)]NPY(24-36), a potent Y2 receptor agonist, shows that it is unstructured in aqueous solution at 5-20 degrees C, but forms a well-defined helix (encompassing residues 25-35) in 40% trifluoroethanol/water at 20 degrees C. Sedimentation experiments show that, in contrast to many peptides in aqueous trifluoroethanol, Ac[Leu(28,31)]NPY(24-36) associates to form a trimer or, more likely, a tetramer in 40% trifluoroethanol, even though it is monomeric in water. This is consistent with the observation of inter-molecular nuclear Overhauser enhancements in trifluoroethanol. Possible models of the associated form that are consistent with the NMR data are described. The relevance of the helical structure observed in trifluoroethanol to the structure of this peptide bound to the NPY Y2 receptor is discussed.

Three-dimensional structure of the Y1 receptor agonist [Leu31, Pro34]NPY as determined by NMR and molecular modeling

The solution structure of the Y1 receptor agonist, porcine [Leu31, Pro34]NPY, has been investigated by two-dimensional NMR and molecular modeling. A complete assignment of the NMR resonances was achieved and 201 inter-residue nuclear Overhauser enhancement spectroscopy (NOESY) connectivities could be identified, comprising several connectivities between the N- and C-terminal segments. A molecular model was calculated by distance geometry, simulated annealing and conjugate gradients energy minimization using the NOE constraints. The results indicate that, like NPY and other peptides of the family, [Leu31, Pro34]NPY adopts a folded hairpin structure with the terminal segments in close proximity. Analysis of the secondary chemical shifts for the CH(alpha)'s and of the temperature dependence of the NH chemical shifts combined with the NOE constraints indicates a tendency toward helix structure for the segment 18-30 and the presence of turn structure for the C-terminal segment (residues 31-36). Native NPY and [Leu31, Pro34]NPY have most of their structures in common but differ slightly in their C-terminal portion. Based on the structures of NPY and of its specific agonists, [Leu31, Pro34]NPY and NPY 13-36, conclusions can be drawn about the structural requirements for binding to the Y1 and Y2 receptor subtypes.

Solution structure of neuropeptide tyrosine 13-36, a Y2 receptor agonist, as determined by NMR

The three-dimensional structure of neuropeptide tyrosine (NPY) 13-36, a specific Y2 receptor agonist, has been investigated by two-dimensional 1H-NMR spectroscopy in solution. Analysis of the double-quantum-filtered correlation spectroscopy (DQFCOSY), total correlation spectroscopy (TOCSY) and nuclear Overhauser enhancement spectroscopy (NOESY) spectra provided a complete assignment of the proton signals. The interproton connectivities observed in the NOESY spectra comprised 166 intraresidue and 95 interresidue distance ranges which were used as constraints for molecular modeling by distance geometry, simulated annealing and energy minimization. The optimal structures are characterized by a helical C-terminal fragment Leu30-Tyr36 and a wide loop from Leu17 to Ser22. The structure of NPY 13-36 is analogous to the structure of NPY under the same solvent conditions. Comparison with other reported Y2 agonists suggests that the helical Leu30-Tyr36 fragment is the most critical for activity.

Conformational analysis of neuropeptide Y segments by CD, NMR spectroscopy and restrained molecular dynamics

Neuropeptide Y (NPY), a peptide amide comprising 36 residue has been shown to act as a potent vasoconstrictor. In order to shed light on the structural requirements for the biological activities with respect to the different prerequisites for affinity to the NPY receptor subtypes Y1 and Y2, in the present study the syntheses and conformational analyses of two C-terminal segments, NPY(18-36) and NPY(13-36), are described. The results obtained by CD measurements, two-dimensional NMR spectroscopy and a conformational refinement of the NMR-derived structure by molecular mechanics stimulations support the findings of previously published structure-activity relationship studies for biologically active and selective compounds. In particular, the alpha-helical conformation as well as an appropriate exposure of the side chains of the critical C-terminal dipeptide within NPY(18-36) are in agreement with the prerequisites proposed for Y2 receptor binding of that segment.

Structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog ANA-NPY

Neuropeptide Y analog ANA-NPY or [Leu-17, Gln-19, Ala-20, Ala-23, Leu-28, Leu-31]NPY(13-36)-amide binds to postjunctional or Y1 receptors to raise blood pressure and to prejunctional or Y2 receptors to inhibit neurotransmitter release. ANA-NPY affects Y2 receptors in the same way as intact NPY but exhibits far less potent effects on Y1 receptors. The structure of ANA-NPY was examined using two-dimensional proton nuclear magnetic resonance spectroscopy. Complete assignment of all backbone and side chain hydrogens was accomplished with totally correlated spectroscopy (TOCSY) experiments providing through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy (NOESY), providing the through-space and sequential backbone connectivities. The tertiary solution structure of the peptide was performed using distance geometry and dynamic simulated annealing. ANA-NPY exhibits a helical structure with strong amphipathic character with a bend around Glu-24 indicating that the C-terminal segment 25-35 forms a single alpha-helical motif.