Protein–carbohydrate interactions: At the heart of biochemistry

Proteins that possess the ability to bind carbohydrates specifically and reversibly abound in nature, being present in all living organisms, from viruses to humans. Their interactions with their ligands are the basis of a myriad of biological processes, both normal and pathological1–3 (Table 1). The high selectivity required for these interactions is provided by a specific stereochemical fit between complementary molecules, the protein on the one hand and the carbohydrate on the other. This concept has its origins in the lock-and-key hypothesis, introduced by Emil Fischer at the end of the 19th Century to explain the specificity of interactions between enzymes (he studied glycosidases) and their substrates (carbohydrates), i.e. between molecules in solution. In time it was extended to describe the interactions of cells with soluble molecules and with other cells.