2013, Vol.42, No.12

Oligosaccharides play pivotal roles in various molecular recognition events on cell surfaces and in intracellular environments. Although information about the three-dimensional structure of oligosaccharides is crucial for understanding the mechanisms underlying their biological functions and for designing drugs targeting carbohydrate recognition systems, their inherent flexibility hampers detailed conformational analysis. NMR spectroscopy has immense potential for providing atomic details of oligosaccharide structures in solution as well as in complexes with other biomolecules. However, the traditional NMR approach based on local conformational information provided by the nuclear Overhauser effect (NOE) is often precluded by insufficient information about long interatomic distances and hydrogen bonds involving hydroxy groups. To address these issues, new NMR techniques have recently been developed, exploiting the effects of introduced paramagnetic probes and stable isotopes to target oligosaccharides. Lanthanoid tagging and the spin labeling of oligosaccharides induce paramagnetic effects such as pseudocontact shift and paramagnetic relaxation enhancement, offering NOE-independent sources of long-distance information. Deuterium-induced isotope shifts of neighboring 13C resonances provide an experimental tool for the identification of hydrogen bonds involving oligosaccharide hydroxy groups. The uniform and position-selective 13C enrichment of oligosaccharides can be achieved by metabolic labeling using genetically engineered yeast cells. Furthermore, small ganglioside-embedding bicelles have been used for detailed NMR analyses of intermolecular interactions involving glycolipids in membrane environments. These NMR approaches, in conjunction with computational simulation, have opened up new vistas for the analysis of oligosaccharide conformations and interactions at atomic level.