title: High-field 1H MAS and 15N CP-MAS NMR studies of alanine tripeptides and oligomers: distinction of antiparallel and parallel beta-sheet structures and two crystallographically independent molecules.
abstract: beta-Strand peptides are known to assemble into either antiparallel (AP) or parallel (P) beta-sheet forms which are very important motifs for protein folding and fibril formations occurring in silk fibroin or amyloid proteins. Well-resolved 1H NMR signals including NH protons were observed for alanine tripeptides (Ala)3 with the AP and P structures as well as (Ala)n (n = 4-6) by high-field/fast magic-angle spinning NMR. Amide NH and amino NH3+ 1H signals of (Ala)3 with the P structure were well resonated at 7.5 and 8.9 ppm, respectively, whereas they were not resolved for the AP structure. Notably, NH 1H signals of (Ala)3 and (Ala)4 taking the P structure are resonated at higher field than those of the AP structure by 1.0 and 1.1 ppm, respectively. Further, NH 15N signals of (Ala)3 with the AP structure were resonated at lower field by 2 to 5 ppm than those of (Ala)3 with the P structure. These relative 1H and 15N hydrogen bond shifts of the P structure with respect to those of the AP structure are consistent with the relative hydrogen bond lengths of the interstrand N-H...O=C bonds. Distinction between the two crystallographically independent chains present in the AP and P structures was feasible by 15N chemical shifts but not by 1H chemical shifts because of insufficient spectral resolution in the latter. Calculated 1H and 15N shielding constants by density functional theory are generally consistent with the experimental data, although some discrepancies remain depending upon the models used.
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16, Nakacho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Michi
authors.initials: M
authors.lastname: Okonogi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Kurosu
authors.forename: Masataka
authors.initials: M
authors.lastname: Tansho
authors.forename: Tadashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Hazime
authors.initials: H
authors.lastname: Saitô
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Asakura
mesh_terms: D000409:Alanine / Q000737:chemistry*; D000465:Algorithms; D000682:Amyloid / Q000737:chemistry; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods; D008280:Magnetics; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011522:Protons
chemical_list: D000682:Amyloid; D009587:Nitrogen Isotopes; D010455:Peptides; D011522:Protons; D000409:Alanine