title: Conformational analysis of the thrombin receptor agonist peptides SFLLR and SFLLR-NH2 by NMR: evidence for a cyclic bioactive conformation.
abstract: The conformational properties of the pentapeptide Ser-Phe-Leu-Leu-Arg (P5), a human thrombin receptor-derived sequence forming part of a tethered ligand which activates the thrombin receptor, and its more active amide derivative Ser-Phe-Leu-Leu-Arg-NH2 (P5-NH2), have been studied by proton NMR spectroscopy in dimethylsulfoxide. Measurements of nuclear Overhauser effects, performed using two-dimensional rotating frame nuclear Overhauser (ROESY) and one-dimensional nuclear Overhauser enhancement (NOE) spectroscopy, revealed that P5 exists mainly in an extended conformation. However, proton-proton 1D-NOEs between Phe C alpha H and Ser C alpha H Leu3 C alpha H and Leu3 NH, and Leu4 C alpha H and Leu4 NH, as well as between the Ser and Arg sidechains, also implicated a minor conformer for P5 having a curved backbone and a near-cyclic structure. In contrast to P5, measurements of NOEs and ROEs for P5-NH2 revealed a more stabilized cyclic structure which may account for its higher biological potency. Thus strong interresidue sequential NH (i)-NH (i + 1) interactions, as well as C-terminal carboxamide to N-terminal side-chain interactions, i.e., Arg CONH2 to Phe ring and Arg CONH2 to Ser C alpha/C beta beta', observed at lower levels of the ROESY spectrum, supported a curved backbone structure for SFLLR-NH2. Since the higher potency P5-NH2 analogue adopts predominantly a cyclic structure, a cyclic bioactive conformation for thrombin receptor agonist peptides is suggested.
authors.affiliation: University of Patras, Department of Chemistry, Greece.
authors.forename: J
authors.initials: J
authors.lastname: Matsoukas
authors.forename: M D
authors.initials: MD
authors.lastname: Hollenberg
authors.forename: T
authors.initials: T
authors.lastname: Mavromoustakos
authors.forename: D
authors.initials: D
authors.lastname: Panagiotopoulos
authors.forename: K
authors.initials: K
authors.lastname: Alexopoulos
authors.forename: R
authors.initials: R
authors.lastname: Yamdagni
authors.forename: Q
authors.initials: Q
authors.lastname: Wu
authors.forename: G J
authors.initials: GJ
authors.lastname: Moore
mesh_terms: D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003500:Cyclization; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry*; D011487:Protein Conformation; D018179:Receptors, Thrombin / Q000819:agonists* / Q000737:chemistry; D016339:Spectrometry, Mass, Fast Atom Bombardment
chemical_list: D010446:Peptide Fragments; D018179:Receptors, Thrombin