title: Conformational flexibility and dynamics of two (1-->6)-linked disaccharides related to an oligosaccharide epitope expressed on malignant tumour cells.
abstract: The conformational flexibility and dynamics of two (1-->6)-linked disaccharides that are related to the action of the glycosyl transferase GnT-V have been investigated. NMR NOE and T-ROE spectroscopy experiments, conformation-dependent coupling constants and molecular dynamics (MD) simulations were used in the analyses. To facilitate these studies, the compounds were synthesised as alpha-d-[6-(13)C]-Manp-OMe derivatives, which reduced the (1)H NMR spectral overlap and facilitated the determination of two- and three-bond (1)H,(1)H, (1)H,(13)C and (13)C,(13)C-coupling constants. The population distribution for the glycosidic omega torsion angle in alpha-d-Manp-(1-->6)-alpha-d-Manp-OMe for gt/gg/tg was equal to 45:50:5, whereas in alpha-d-Manp-OMe it was determined to be 56:36:8. The dynamic model that was generated for beta-d-GlcpNAc-(1-->6)-alpha-d-Manp-OMe by MD simulations employing the PARM22/SU01 CHARMM-based force field was in very good agreement with experimental observations. beta-d-GlcpNAc-(1-->6)-alpha-d-Manp-OMe is described by an equilibrium of populated states in which the phi torsion angle has the exo-anomeric conformation, the psi torsion angle an extended antiperiplanar conformation and the omega torsion angle a distribution of populations predominantly between the gauche-trans and the gauche-gauche conformational states (i.e., gt/gg/tg) is equal to 60:35:5, respectively. The use of site-specific (13)C labelling in these disaccharides leads to increased spectral dispersion, thereby making NMR spectroscopy based conformational analysis possible that otherwise might be difficult to attain.
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91 Stockholm, Sweden.
authors.forename: Ulrika
authors.initials: U
authors.lastname: Olsson
authors.forename: Elin
authors.initials: E
authors.lastname: Säwén
authors.forename: Roland
authors.initials: R
authors.lastname: Stenutz
authors.forename: Göran
authors.initials: G
authors.lastname: Widmalm
mesh_terms: D002236:Carbohydrate Conformation; D003198:Computer Simulation; D000939:Epitopes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009844:Oligosaccharides / Q000737:chemistry*
chemical_list: D000939:Epitopes; D009844:Oligosaccharides