title: SMS 201-995, a very potent analogue of somatostatin. Assignment of the 1H 500 MHz n.m.r. spectra and conformational analysis in aqueous solution.
abstract: The conformations of a cyclic analogue of somatostatin, SMS 201-995, have been studied by n.m.r. spectroscopy at 500 MHz in aqueous solution. Assignments were made by use of 2D-correlated methods, especially by detecting long-range connectivities in order to identify the aromic amino-acid and long-range couplings between alpha protons of consecutive residues. Measurements of temperature coefficients of amide protons and of NH-C alpha H coupling constants enabled us to conclude that in water the molecule is rather flexible, with no evidence for a beta turn structure involving Thr6. An equilibrium involving two gamma turn conformations stabilized respectively by Cys2-D-Trp4 and Phe3-Lys5 hydrogen bonds, is responsible for the large upfield shift observed for the Lys5 gamma protons and is compatible with the measured JNH-C alpha H coupling constants.
authors.forename: C
authors.initials: C
authors.lastname: Wynants
authors.forename: G
authors.initials: G
authors.lastname: Van Binst
authors.forename: H R
authors.initials: HR
authors.lastname: Loosli
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D015282:Octreotide; D011487:Protein Conformation; D013004:Somatostatin / Q000031:analogs & derivatives*; D013816:Thermodynamics
chemical_list: D013004:Somatostatin; D015282:Octreotide