title: Molecular and crystal structures of Aib-containing oligopeptides Boc-Leu4-Aib-Leu4-OBzl and Boc-(Leu4-Aib)2-OBzl.
abstract: Sample peptides Boc-Leu4-Aib-Leu4-OBzl and Boc-(Leu4-Aib)2-OBzl, were crystallized by the solvent-evaporation method. Both crystals are monoclinic, with space group of P2(1) and Z = 2. The cell parameters are a = 16.580 (7), b = 21.105 (7), c = 11.583 (4) A, and beta = 104.90 (3) degrees (Boc-Leu4-Aib-Leu4-OBzl), and a = 15.247 (9), b = 19.04 (1), c = 16.311 (9) A, and beta = 117.10 (1) degrees [Boc-(Leu4-Aib)2-OBzl]. Crystal structures were solved by the direct method and refined to R values of 0.096 (the former peptide) and 0.112 (the latter). Peptide backbones fold into a right-handed alpha-helix, except for the C-terminal Aib residue in Boc-(Leu4-Aib)2-OBzl. Both peptide molecules are stabilized by six (the former) or seven (the latter) intramolecular (5----1) hydrogen bonds, and arranged in the head-to-tail fashion, which makes an infinite column. In this column, one (the former) or two (the latter) intermolecular hydrogen bonds link the neighboring molecules. In the case of Boc-Leu4-Aib-Leu4-OBzl, the solvent molecule N,N-dimethylformamide was found in the difference Fourier map. There was a hydrogen bond between peptide and solvent molecule. Along the lateral direction, only hydrophobic contacts were observed between adjacent peptide molecules.
authors.affiliation: Faculty of Technology, Tokyo University of Agriculture and Technology, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Okuyama
authors.forename: Y
authors.initials: Y
authors.lastname: Saga
authors.forename: M
authors.initials: M
authors.lastname: Nakayama
authors.forename: M
authors.initials: M
authors.lastname: Narita
mesh_terms: D000595:Amino Acid Sequence; D000621:Aminoisobutyric Acids / Q000737:chemistry*; D003460:Crystallization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000621:Aminoisobutyric Acids; D009842:Oligopeptides; C072804:tert-butoxycarbonylleucyl-leucyl-leucyl-leucyl-aminoisobutyryl-leucyl-leucyl-leucyl-leucine benzyl ester; C072803:t-butoxycarbonylleucyl-leucyl-leucyl-leucyl-aminoisobutyryl-leucyl-leucyl-leucyl-leucyl-aminoisobutyric acid benzyl ester