Structure and conformation of complex carbohydrates of glycoproteins, glycolipids, and bacterial polysaccharides

For nuclear magnetic resonance determinations of the conformation of oligos accharides in solution, simple molecular mechanics calculations and nuclear Overhauser enhancement measurements are adequate for small oligosaccharide s that adopt single, relatively rigid conformations. Polysaccharides and la rger or more flexible oligosaccharides generally require additional types o f data, such as scalar and dipolar coupling constants, which are most conve niently measured in C-13-enriched samples. Nuclear magnetic resonance relax ation data provide information on the dynamics of oligosaccharides, which i nvolves several different types of internal motion. Oligosaccharides comple xed with lectins and antibodies have been successfully studied both by X-ra y crystallography and by nuclear magnetic resonance spectroscopy. The compl exes have been shown to be stabilized by a combination of polar hydrogen bo nding interactions and van der Waals attractions. Although theoretical calc ulations of the conformation and stability of free oligosaccharides and of complexes with proteins can be carried out by molecular mechanics methods, the role of solvent water for these highly polar molecules continues to pre sent computational problems.