The structural basis for carbohydrate recognition by lectins.

1. Different carbohydrate-specific proteins, such as lectins, may combine with the same monosaccharide or oligosaccharide by different H-bonding and hydrophobic side chains. 2. Homologous proteins with distinct specificities may bind different monosaccharides (e.g., for glucose and galactose that differ in the configuration of a single hydroxyl) by the same set of invariant residues that are identically positioned in their tertiary structures. 3. The energetics of protein-carbohydrate interactions cannot be derived from structural information. 4. Nature solves in a variety of different ways the problem of constructing combining sites for carbohydrates, just as it provides diverse solutions for other functions of proteins.