CONFORMATIONAL PROPERTIES OF THE PROLINE REGION OF PORCINE NEUROPEPTIDE-Y BY CD AND H-1-NMR SPECTROSCOPY

We synthesized porcine neuropeptide Y(pNPY) N-terminal fragments by so lid-phase synthesis techniques and analyzed them for solution conforma tional properties by CD and H-1-nmr spectroscopy. The analogues pNPY(1 -9) and PNPY1-14 displayed CD spectra indicative of random structures and showed no evidence for induced alpha-helical structures in trifluo roethanol (TFE) lip to 50%. However, the CD spectra of pNPY(1-9) sugge sted a conformational shift in tetrahyduofuran. Although in aqueous so lution the CD spectra of pNPY(1-21) indicated random structures with i nduction of only a small percentage of alpha-helix in aqueous TFE, pNP Y(1-25) displayed 13% alpha-helical structure in aqueous solution that increased to 40 and 41% by the addition of TFE and methanol, respecti vely. The nmr spectra of pNPY(1-9) and the proline region of pNPY(1-9) indicated extended structures with all-trans conformers at Pro5 and P ro8 for pNPY(1-9) and at Pro5, Pro8, and Pro13 for pNPY(1-25); in each case the Tyr1-Pro2 amide bond was in both cis and trans conformations However, observed nuclear Overhauser effect correlations and HN excha nge experiments indicated an or-helical segment in pNPY(1-25) initiate d by Pro13 and extending from residues 14 to 25. Thus, the N-terminal polyproline region of NPY has no propensity to fold into a regular sec ondary structure, although Puo13 is a helix initiator, a result consis tent with the proposed role of this amino acid in the NPY structural m odel. (C) 1995 John Wiley & Sons, Inc.