title: Competitive formation of 10- and 7-membered hydrogen-bonded rings of proline-containing model peptides.
abstract: Intramolecularly hydrogen-bonded structures of proline-containing model peptides with a sequence of N-tert-butoxycarbonyl-prolyl-Xaa-NHCH3 [Xaa = Gly (glycyl), Ala (alanyl), Phe (phenylalanyl), Leu (leucyl), Ile (isoleucyl), and Val (valyl)] were studied by proton nuclear magnetic resonance and infrared spectroscopy. Variation of chemical shifts of amide protons with composition change of DMSO-d6/CDCl3 mixed solvents were found to be a good measure of intramolecular hydrogen bonding of peptides in CDCl3 solution. It has been shown that 10- and 7-membered hydrogen-bonded rings, which should have the beta- and gamma-turn like structures in proteins, respectively, form competitively with each other. It is suggested that the equilibrium between the two hydrogen-bonded rings is determined by steric hindrance due to a side chain of the Xaa residue. Free energies for formation of the 10- and 7-membered hydrogen-bonded rings, deltaG10 and deltaG7, were estimated from the solvent composition-dependent change of the chemical shifts. A good correlation between deltaG10 and the occurrence frequencies of residues Xaa at the (i + 2)th position for the beta-turns in proteins has been found.
authors.affiliation: Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Jin
authors.forename: Kenji
authors.initials: K
authors.lastname: Tonan
authors.forename: Shun-ichi
authors.initials: S
authors.lastname: Ikawa
mesh_terms: D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics
chemical_list: D009842:Oligopeptides; D011392:Proline