title: A 1H and 13C NMR study on the role of salt-bridges in the formation of a type I beta-turn in N-acetyl-L-Asp-L-Glu-L-Lys-L-Ser-NH2.
abstract: The conformation of the tetrapeptide N-Acetyl-Asp7-Glu8-Lys9-Ser10-NH2, a fragment of the type I collagen alpha-1 chain N-telopeptide, has been studied by 1H and 13C NMR and circular dichroism spectroscopy. The spectroscopic evidence, based on two-dimensional, phase-sensitive NMR techniques such as COSY, ROESY, proton-carbon shift correlation and selective COLOC, indicates a strong dependence of the conformation on the experimental conditions. In CD3OH/H2O (60/40) at ca. neutral pH the tetrapeptide forms a beta-turn, stabilized by a hydrogen bond between NH(S10) and CO(D7) and a strong salt-bridge between COO-(E8) and NH3+(K9). The beta-turn is type I and appears to coexist with a non-hydrogen-bonded structure. The coexistence of these two conformers is proven by proton NMR data such as NH-NH ROEs, reduced NH-H alpha (E8) coupling constant, NH(E8) low-field shift and the temperature coefficient of NH(S10), whereas the conclusion regarding the salt-bridge is based on 13C results. In the same solvent, at a pH below the pKa of the carboxyl groups, no evidence for a conformation other than extended can be found. In aqueous solution at approximately neutral pH, evidence for the E8-K9 charge interaction is observed, but not for a hydrogen bond anywhere in the molecule.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Otter
authors.forename: P G
authors.initials: PG
authors.lastname: Scott
authors.forename: X H
authors.initials: XH
authors.lastname: Liu
authors.forename: G
authors.initials: G
authors.lastname: Kotovych
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003094:Collagen; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D011487:Protein Conformation; D012997:Solvents; D013816:Thermodynamics
chemical_list: D012997:Solvents; D003094:Collagen