Conformational properties of the proline region of porcine neuropeptide Y by CD and 1H-nmr spectroscopy

• Published in: Biopolymers Vol. 35; no. 6; p. 583
• Main Authors: Chu, S S, Velde, D V, Shobe, D, Balse, P, Doughty, M B
• Format: Journal Article
• Language: English
• Published: United States 01.06.1995
• Subjects: Amino Acid Sequence; Animals; Circular Dichroism; Hydrogen; Indicators and Reagents; Magnetic Resonance Spectroscopy - methods; Molecular Sequence Data; Neuropeptide Y - chemistry; Peptide Fragments - chemical synthesis; Peptide Fragments - chemistry; Proline; Protein Conformation; Protein Structure, Secondary; Swine
• ISSN: 0006-3525
• DOI: 10.1002/bip.360350604

We synthesized porcine neuropeptide Y (pNPY) N-terminal fragments by solid-phase synthesis techniques and analyzed them for solution conformational properties by CD and 1H-nmr spectroscopy. The analogues pNPY1-9 and pNPY1-14 displayed CD spectra indicative of random structures and showed no evidence for induced alpha-helical structures in trifluoroethanol (TFE) up to 50%. However, the CD spectra of pNPY1-9 suggested a conformational shift in tetrahydrofuran. Although in aqueous solution the CD spectra of pNPY1-21 indicated random structures with induction of only a small percentage of alpha-helix in aqueous TFE, pNPY1-25 displayed 13% alpha-helical structure in aqueous solution that increased to 40 and 41% by the addition of TFE and methanol, respectively. The nmr spectra of pNPY1-9 and the proline region of pNPY1-25 indicated extended structures with all-trans conformers at Pro5 and Pro8 for pNPY1-9 and at Pro5, Pro8, and Pro13 for pNPY1-25; in each case the Tyr1-Pro2 amide bond was in both cis and trans conformations. However, observed nuclear Overhauser effect correlations and HN exchange experiments indicated an alpha-helical segment in pNPY1-25 initiated 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 secondary structure, although Pro13 is a helix initiator, a result consistent with the proposed role of this amino acid in the NPY structural model.