Stabilization of the Helical Structure of Y2-Selective Analogues of Neuropeptide Y by Lactam Bridges

Abstract

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.

Anticonvulsant neuropeptides as drug leads for neurological diseases

“…157,158 Lactam bridges were introduced into the peptide fragments at various positions, with differing lengths (Lys/Glu or Orn/Asp), and different positions of the amide linkage (CO/NH or NH/ CO). Of these analogs, Ac-cyclo28/32[Lys28, Glu32]NPY24-36 was found to have the greatest Y 2 affinity; 157 its in-solution structure was determined by NMR, [159][160][161] and it was found to act as a Y 2 agonist. 162 It was postulated that the central amino acids play purely structural (rather than functional) roles, and the alanine scan showed that they were non-essential for binding to the Y 1 receptor.…”

Over One Hundred Peptide-Activated G Protein-Coupled Receptors Recognize Ligands with Turn Structure

“…NMR solution structures are also available for all three peptides. − The C-terminal helical region of NPY is responsible for biological activity. , Mimetics of the neuropeptide Y helical region are potent antagonists of NPY, and exhibit anti-hypertensive and neuromodulatory activity. An example is the helix in the cyclic NPY analogue 87 , Ac[A24,K28,L31, E32]NPY(24−36), its helical structure being stabilized by a lactam bridge …”

Are Hormones from the Neuropeptide Y Family Recognized by Their Receptors from the Membrane‐Bound State?

“…[61] Other authors have investigated mutants of truncated or cyclized versions of NPY. [62][63][64][65][66] Keire et al also estimated from CD and NMR spectra the helical content of PYY and the highly Y2-subtype-specific PYY fragment PYY . [67] The calculated helicity for PYY is 42 % and for PYY(3-36) is only 23 %, a result showing that the removal of two N-terminal amino acids resulted in major conformational alterations in solution; this observation was confirmed by our own dynamics data on PYY(3-36) (see below).…”