title: A conformational study of the xyloglucan oligomer, XXXG, by NMR spectroscopy and molecular modeling.
abstract: A structural study of the XXXG xyloglucan heptasaccharide (X = alpha-D-Xylp(1 --> 6)-beta-D-Glcp and G = beta-D-Glcp) isolated from apple fruit has been undertaken with nmr and molecular mechanics methods. Quantitative 400 MHz nmr data including nuclear Overhauser effect spectroscopy (NOESY) volumes were recorded at both 6 and 20 degrees C. In spite of severe overlapping of resonances, it was possible to estimate summed NOEs for the majority of the anomeric and glucosyl methylene protons. An ensemble-average population of preferred geometries has been established with the CICADA conformational searching algorithm associated with the MM3 force field. Comparison of the theoretical data obtained by back-calculation of the NOESY volumes from the ensemble-average distance matrix program and motional models based on the Stokes-Einstein-Debye relation satisfactorily reproduce the experimental data. Conformational averaging about the mainchain glycosidic linkages includes both the syn and anti conformers and a minor gauche-gauche population is highly probable. The theoretical data overestimate the syn preference of the Glc(c) --> Glc(b) linkage as well as the Glc(c) GT rotamer population. Finally, both the motional models and the conformational search indicate a fairly rigid backbone and greater flexiblity for the xylose side chains.
authors.affiliation: Département de Chimie, URA 1679, Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France.
authors.forename: C
authors.initials: C
authors.lastname: Picard
authors.forename: J
authors.initials: J
authors.lastname: Gruza
authors.forename: C
authors.initials: C
authors.lastname: Derouet
authors.forename: C M
authors.initials: CM
authors.lastname: Renard
authors.forename: K
authors.initials: K
authors.lastname: Mazeau
authors.forename: J
authors.initials: J
authors.lastname: Koca
authors.forename: A
authors.initials: A
authors.lastname: Imberty
authors.forename: C
authors.initials: C
authors.lastname: Hervé Du Penhoat
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D003198:Computer Simulation; D004187:Disaccharides / Q000737:chemistry; D005638:Fruit / Q000737:chemistry; D005936:Glucans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011134:Polysaccharides / Q000737:chemistry*; D019685:Rosales / Q000737:chemistry; D013816:Thermodynamics; D014990:Xylans
chemical_list: D004187:Disaccharides; D005936:Glucans; D011134:Polysaccharides; D014990:Xylans; C029353:xyloglucan