Conformational properties of the proline region of porcine neuropeptide Y by CD and 1H-nmr spectroscopy.
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.
Chu
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SS
Department of Medicinal Chemistry, University of Kansas, Lawrence 66045, USA.
Velde
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Shobe
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Balse
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Doughty
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D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D006859:Hydrogen; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008969:Molecular Sequence Data; D009478:Neuropeptide Y / Q000737:chemistry*; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry*; D011392:Proline; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013552:Swine
D007202:Indicators and Reagents; D009478:Neuropeptide Y; D010446:Peptide Fragments; D006859:Hydrogen; D011392:Proline