Conformational studies on a unique bis-sulfated glycolipid using NMR spectroscopy and molecular dynamics simulations

The time-averaged solution conformation of a unique bis-sulfated glycolipid (HSO3)2-2,6Manα-2Glcα-1-sn-2,3-O-alkylglycerol, was studied in terms of the torsional angles of two glycosidic linkages, φ (H1-C1-O-Cx) and ψ (C1-O-Cx-Hx), derived from heteronuclear three-bond coupling constants (3JC,H), and inter-residual proton–proton distances from J-HMBC 2D and ROESY experiments, respectively. The dihedral angles of Glcα1Gro in glycolipids were determined for the first time. The C1-C4 diagonal line of the α-glucose ring makes an angle of ≈ 120 ° with the glycerol backbone, suggesting that the α-glucose ring is almost parallel to the membrane surface in contrast with the perpendicular orientation of the β-isomer. Furthermore, minimum-energy states around the conformation were estimated by Monte Carlo/stochastic dynamics (MCSD) mixed-mode simulations and the energy minimization with assisted model building and energy refinement (AMBER) force field. The Glcα1Gro linkage has a single minimum-energy structure. On the other hand, three conformers were observed for the Manα2Glc linkage. The flexibility of Manα2Glc was further confirmed by the absence of inter-residual hydrogen bonds which were judged from the temperature coefficients of the chemical shifts, dδ/dT (−10−3 p.p.m.·°C−1), of hydroxy protons. The conformational flexibility may facilitate interaction of extracellular substances with both sulfate groups.