title: Comparison of proline and N-methylnorleucine induced conformational equilibria in cyclic pentapeptides.
abstract: The cyclic, imido acid containing pentapeptides cyclo(Asp-Trp-(NMe)Nle-Asp-Phe) (cpp[NMeNle(3)]) and cyclo(Asp-Trp-Pro-Asp-Phe) (cpp[Pro(3)]) have been investigated by 1H-NMR spectroscopy in DMSO and by restrained molecular dynamics methods. The spectra indicate the existence of at least four cis/trans isomers for cpp[NMeNle(3)] and two cis/trans isomers for cpp[Pro(3)]. In addition to the imido peptide bonds, cpp[NMeNle(3)] shows cis/trans isomerization of the Asp4-Phe5 and Phe5-Asp1 peptide bonds whereas only the Phe5-Asp1 peptide bond isomerizes in the Pro-containing peptide. In cpp[Pro(3)] all cis bonds are centred in betaVIb turns. Also, cpp[NMeNle(3)] prefers backbone angles around the cis bonds which are rather similar to the angles of a betaVIb turn. The higher number of cis/trans isomers and slight deviations in the backbone angles of comparable isomers of both peptides are caused by an enhanced flexibility of cpp[NMeNle(3)] due to the possibility of the phi-(NMe)Nle rotation.
authors.affiliation: Humboldt Universitat zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Chemie, Berlin, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Weisshoff
authors.forename: T
authors.initials: T
authors.lastname: Wieprecht
authors.forename: P
authors.initials: P
authors.lastname: Henklein
authors.forename: C
authors.initials: C
authors.lastname: Frömmel
authors.forename: C
authors.initials: C
authors.lastname: Antz
authors.forename: C
authors.initials: C
authors.lastname: Mügge
mesh_terms: D000595:Amino Acid Sequence; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009646:Norleucine / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry; D010456:Peptides, Cyclic / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D009842:Oligopeptides; D010456:Peptides, Cyclic; D009646:Norleucine; D011392:Proline