title: Mimicry of beta II'-turns of proteins in cyclic pentapeptides with one and without D-amino acids.
abstract: The solution structure of eight cyclic pentapeptides has been determined by two-dimensional 1H-NMR spectroscopy combined with spectra simulations and restrained molecular dynamic simulations. Six of the cyclic pentapeptides were derived from the C-terminal cholecystokinin fragment CCK-4 enlarged with Asp1 resulting in the sequence (Asp-Trp-Met-Asp-Phe), one L-amino acid after the other was substituted by its D-analog. In addition, two peptides, including an all-L-amino-acid-containing cyclic pentapeptide, cyclo(Asp-Phe-Lys-Ala-Thr) and cyclo(Asp-Phe-Lys-Ala-D-Thr) were investigated. All D-amino-acid-containing peptides show beta II'-turn conformations with the D-amino acid in the i + 1 position, excepting the D-aspartic-acid-containing peptides. These two peptides are characterized by the lack of beta-turns at pH values less than 4, suggesting that D-aspartic acid in the full-protonized state avoids the formation of beta-turns in these compounds. At pH values greater than 5, a conformational change into the beta II'-turn conformation was also observed for these peptides. Conformations without beta-turns are expected for cyclic all-L pentapeptides, but both cyclo(Asp-Phe-Lys-Ala-Thr) and the D-Thr analog cyclo(Asp-Phe-Lys-Ala-D-Thr) exhibit beta II'-turn conformations around Thr-Asp and D-Thr-Asp. Thus cyclic all-L pentapeptides and those with one D-amino acid are able to form similar structures preferably with a beta II'-turn. The beta-turn formation in cyclic pentapeptides containing a D-aspartic acid is dependent on the ionization state. The relevance of the work to the design of beta'-turn mimetics is discussed.
authors: Institute of Chemistry, Humboldt University Berlin, Germany.
authors: H
authors: H
authors: Weisshoff
authors: C
authors: C
authors: Präsang
authors: P
authors: P
authors: Henklein
authors: C
authors: C
authors: Frömmel
authors: A
authors: A
authors: Zschunke
authors: C
authors: C
authors: Mügge
mesh_terms: D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010446:Peptide Fragments / Q000737:chemistry; D010456:Peptides, Cyclic / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013758:Tetragastrin / Q000737:chemistry
chemical_list: D010446:Peptide Fragments; D010456:Peptides, Cyclic; D013758:Tetragastrin