The solution conformation of sialyl-alpha (2----6)-lactose studied by modern NMR techniques and Monte Carlo simulations.
We present a comprehensive strategy for detailed characterization of the solution conformations of oligosaccharides by NMR spectroscopy and force-field calculations. Our experimental strategy generates a number of interglycosidic spatial constraints that is sufficiently large to allow us to determine glycosidic linkage conformations with a precision heretofore unachievable. In addition to the commonly used [1H,1H] NOE contacts between aliphatic protons, our constraints are: (a) homonuclear NOEs of hydroxyl protons in H2O to other protons in the oligosaccharide, (b) heteronuclear [1H,13C] NOEs, (c) isotope effects of O1H/O2H hydroxyl groups on 13C chemical shifts, and (d) long-range heteronuclear scalar couplings across glycosidic bonds. We have used this approach to study the trisaccharide sialyl-alpha (2----6)-lactose in aqueous solution. The experimentally determined geometrical constraints were compared to results obtained from force-field calculations based on Metropolis Monte Carlo simulations. The molecule was found to exist in 2 families of conformers. The preferred conformations of the alpha (2----6)-linkage of the trisaccharide are best described by an equilibrium of 2 conformers with phi angles at -60 degrees or 180 degrees and of the 3 staggered rotamers of the omega angle with a predominant gt conformer. Three intramolecular hydrogen bonds, involving the hydroxyl protons on C8 and C7 of the sialic acid residue and on C3 of the reducing-end glucose residue, contribute significantly to the conformational stability of the trisaccharide in aqueous solution.
Poppe
L
L
Department of Biochemistry, University of Georgia, Athens 30602.
Stuike-Prill
R
R
Meyer
B
B
van Halbeek
H
H
D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D007785:Lactose / Q000031:analogs & derivatives* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009010:Monte Carlo Method; D012794:Sialic Acids / Q000737:chemistry*
D012794:Sialic Acids; C000020:N-acetylneuraminoyllactose; D007785:Lactose