title: Switching of turn conformation in an aspartate anion peptide fragment by NH . . . O- hydrogen bonds.
abstract: Aspartic acid protease model peptides Z-Phe-Asp(COOH)-Thr-Gly-Ser-Ala-NHCy (1) and AdCO-Asp(COOH)-Val-Gly-NHBzl (3), and their aspartate anions (NEt4)[Z-Phe-Asp(COO-)-Thr-Gly-Ser-Ala-NHCy] (2) and (NEt4)[AdCO-Asp(COO-)-Val-Gly-NHBzl] (4), having an invariant primary sequence of the Asp-X(Thr,Ser)-Gly fragment, were synthesized and characterized by 1H-NMR, CD, and infrared (IR) spectroscopies. NMR structure analyses indicate that the Asp O(delta) atoms of the aspartate peptide 2 are intramolecularly hydrogen-bonded with Gly, Ser, Ala NH, and Ser OH, supporting the rigid beta-turn-like conformation in acetonitrile solution. The tripeptide in the aspartic acid 3 forms an inverse gamma-turn structure, which is converted to a beta-turn-like conformation because of the formation of the intramolecular NH . . . O- hydrogen bonds with the Asp O(delta) in 4. Such a conformational change is not detected between dipeptides AdCO-Asp(COOH)-Va-NHAd (5) and (NEt4)[AdCO-Asp(COO-)-Val-NHAd] (6). The pK(a) value of side-chain carboxylic acid (5.0) for 3 exhibits a lower shift (0.3 unit) from that of 5 in aqueous polyethyleneglycol lauryl ether micellar solution. NMR structure analyses for 3 in an aqueous micellar solution indicate that the preorganized turn structure, which readily forms the NH . . . O- hydrogen bonds, lowers the pK(a) value and that resulting hydrogen bonds stabilize the rigid conformation in the aspartate anion state. We found that the formation of the NH . . . O- hydrogen bonds involved in the hairpin turn is correlated with the protonation and deprotonation state of the Asp side chain in the conserved amino acid fragments.
authors.affiliation: Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Onoda
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Yamada
authors.forename: Keonil
authors.initials: K
authors.lastname: Lee
authors.forename: Seiji
authors.initials: S
authors.lastname: Adachi
authors.forename: Taka-Aki
authors.initials: TA
authors.lastname: Okamura
authors.forename: Kumiko
authors.initials: K
authors.lastname: Yoshizawa-Kumagaye
authors.forename: Kiichiro
authors.initials: K
authors.lastname: Nakajima
authors.forename: Toru
authors.initials: T
authors.lastname: Kawakami
authors.forename: Saburo
authors.initials: S
authors.lastname: Aimoto
authors.forename: Norikazu
authors.initials: N
authors.lastname: Ueyama
mesh_terms: D000595:Amino Acid Sequence; D000838:Anions / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D000838:Anions; D009842:Oligopeptides; D010446:Peptide Fragments; D001224:Aspartic Acid