A Path to Complex Carbohydrates

Glycans are carbohydrate-containing compounds that include oligosaccharides as well as the carbohydrate parts of glycoproteins or glycolipids. All cells contain glycans, ranging from those that benefit from the development, metabolism, and immune responses of the host to those involved in cancer metastasis or hostpathogen interactions ( 1 ). The oligosaccharide sequence of a glycan determines which proteins it binds to and can thus profoundly influence its physiological activity. The full complement of glycans has not been determined for any cell type, but recent analyses of known mammalian glycans have revealed that there are underlying sequence patterns ( 2 , 3 ). It remains difficult to assign functions to specific glycan sequences because the relevant oligosaccharides cannot easily be accessed either by synthesis or by isolation from cells ( 4 ). On page 379 of this issue, Wang et al. report a general and efficient strategy for generating diverse glycans ( 5 ).