title: Lamellar structure in poly(ala-gly) determined by solid-state NMR and statistical mechanical calculations.
abstract: Lamellar structure of poly(Ala-Gly) or (AG)n in the solid was examined using 13C solid-state NMR and statistical mechanical approaches. Two doubly labeled versions, [1-13C]Gly14[1-13C]Ala15- and [1-13C]Gly18[1-13C]Ala19 of (AG)15 were examined by two-dimensional (2D) 13C spin diffusion NMR in the solid state. In addition five doubly labeled [15N,13C]-versions of the same peptide, (AG) 15 and 15 versions labeled [3-13C] in each of the successive Ala residues were utilized for REDOR and 13C CP/MAS NMR measurements, respectively. The observed spin diffusion NMR spectra were consistent with a structure containing a combination of distorted beta-turns with a large distribution of the torsion angles and antiparallel beta-sheets. The relative proportion of the distorted beta-turn form was evaluated by examination of 13C CP/MAS NMR spectra of [3-13C]Ala-(AG)15. In addition, REDOR determinations showed five kinds of atomic distances between doubly labeled 13C and 15N nuclei which were also interpreted in terms of a combination of beta-sheets and beta-turns. Our statistical mechanical analysis is in excellent agreement with our Ala Cbeta 13C CP/MAS NMR data strongly suggesting that (AG)15 has a lamellar structure.
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan. asakura@cc.tuat.ac.jp
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Asakura
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Sato
authors.forename: Fumika
authors.initials: F
authors.lastname: Moro
authors.forename: Yasumoto
authors.initials: Y
authors.lastname: Nakazawa
authors.forename: Akihiro
authors.initials: A
authors.lastname: Aoki
mesh_terms: D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D011108:Polymers; D047011:Silk / Q000737:chemistry*
chemical_list: D007202:Indicators and Reagents; D010455:Peptides; D011108:Polymers; D047011:Silk; C034500:poly(alanylglycine)